A new NEC is on tap, with some of the most far-reaching changes ever made as we begin the next 100 years of the Code. Part 4 of a 4-part series.
This analysis of the changes represented in the 1996 edition of the National Electrical Code (NEC) covers only the most significant of the many changes. Some of those changes were indeed major, including seven new articles, (with another article deleted), and others were for very minor editorial reasons. Major or minor, if you are involved with the particular subject matter, the most minor change can assume major proportions in unexpected ways. Every proposal was made for a reason, and this magazine article is no substitute for careful study of the Code itself. This month's issue covers from Chapter 6 to the end of the book.
Art. 600. This article has been completely rewritten to bring it up to date with current practice in the industry. Virtually every section includes substantive changes, and even for those few that didn't change, they have been split up and relocated in the restructuring that resulted. The most significant new material follows:
Sec. 600-2. A new section has been added on definitions:
Note the distinction between the standard industry term "neon tubing" and electric-discharge lighting, which is much broader. Also note that the term "neon tubing" applies whether or not the actual gas used is neon.
* Electric-Discharge Lighting: Systems of illumination utilizing fluorescent lamps, high intensity discharge (HID) lamps, or neon tubing.
* Neon Tubing: Electric discharge tubing manufactured into shapes, which form letters, parts of letters, skeleton tubing, outline lighting, other decorative elements, or art forms, and filled with various inert gases.
* Sign Body: A portion of a sign, which may provide protection from the weather, but is not an electrical enclosure.
* Skeleton Tubing: Neon tubing that is itself the sign or outline lighting and not attached to an enclosure or sign body.
Sec. 600-3. All electric signs and outline lighting must be listed and installed in accordance with any provisions of that listing, unless otherwise approved by special permission. There are two exceptions:
* (Ex. 1) Field installed skeleton tubing.
* (Ex. 2) Outline lighting consisting of listed lighting fixtures and wired in accordance with Chapter 3.
This section (the old Sec. 600-4) now includes outline lighting within the listing requirement, but the new exceptions exclude the majority of these uses. Ex. 1 relieves this requirement and reverts to Part B on field installed skeleton tubing, which cannot be listed in a factory. Part B has been rewritten to directly address these field installations.
All other manufactured signs and outline lighting using neon tubing must be listed (unless the AHJ gives special permission). For this reason, some former requirements have been deleted and left to the judgment of the testing laboratories. These include former Sec. 600-23 on mechanical securing of conductors in sign troughs, and some subsections in former Sec. 600-34 and -37.
The second exception recognizes that outline lighting that is a sequence of otherwise acceptable, independently installable fixtures can rely on conventional code rules without requiring a coordinated listing. Note that the exception refers to "fixtures" and not lampholders. This is probably an oversight because the context certainly would seem to include the traditional (and fully listed) 4 1/2-in. porcelain or polymeric lampholders that mount to outlet boxes, and similar lampholders that mount to conduit bodies and surface metal raceway.
However, technically, a lampholder is not a fixture and you should consult the AHJ to see how this exception will be interpreted. Note that former Sec. 600-22 on lampholders has not been carried over to the rewritten article. The requirements in Sec. 410-47 and Sec. 410-49, together with listing restrictions, fully cover those requirements during field wiring. Therefore, the fact that this material (old Sec. 600-22) wasn't carded forward further supports the idea that such lampholders can be independently installed under this exception.
Sec. 600-5. This section covers branch circuit requirements, as covered in the old Sec. 600-6. There are substantive changes, however:
* Sec. 600-5(a) on the mandatory sign circuit for commercial occupancies and tenant spaces now requires the outlet top be "at each" entrance.
The old requirement said "outside the entrance," which raised questions if there were more than one entrance. In addition, the old wording required the outlet to be on the outside of the occupancy, even if no sign were ever installed. The resulting weatherproof box was controversial, particularly in cases where local ordinances forbid electric signs in certain zoning districts.
* The exception for service hallways has been clarified.
The former rule classified these hallways as not being "outside the occupancy," which was difficult to interpret, particularly in the usual case where it was factually untrue. The revised wording relates pedestrian access, which is a little closer to the real meaning. The required sign outlet is in a commercial occupancy, and the rule sets a minimum degree of safety consistent with commercial practice.
* The maximum branch-circuit rating rule [Sec. 600-5(b)] has been clarified thanks to the new definitions. Only neon tubing installations are eligible for 30A branch circuits; the others must stay with 20A.
The former rule was somewhat unclear since both HID and neon tubing are forms of electric-discharge lighting. The requirement to compute the load on this circuit at a minimum of 1200VA has been retained as paragraph (3) of this subsection.
* The general wiring method rules have been relocated here, as subsection (c).
Branch circuit wiring can terminate within the sign or outline lighting system enclosure, or in a box or conduit body. These last are commonly used, but weren't recognized in the former Sec. 600-3. The exception to that section has been carried over as a new paragraph (2) here as well. This allows sign or outline lighting enclosures to feed adjacent enclosures for similar purposes. The old restriction on maximum overcurrent protection for these branches being set at 30A has been dropped. Finally, the allowance [formerly in Sec. 600-21(a)] for metal poles complying with Sec. 410-15(b) to support signs has been carried over, as new paragraph (3).
Sec. 600-6. The rules in the former Sec. 600-2(a) for required disconnecting means have been changed and relocated here, as Sec. 600-6(a). Former Sec. 600-2(b) on the required ratings for transformer control devices is now Sec. 600-6(b), with only a minor editorial change.
As in the prior code, a disconnect must be in sight of all electric signs and outline lighting systems. For cord-connected signs the plug can be the disconnect, and the rule is waived entirely for exit directional signs, whether or not connected to an emergency circuit. The prior reference to Art. 700 has been deleted.
The required disconnect location depends on whether or not there is an electronic or electromechanical controller in the circuit. If there is no such controller, then the rule is very clear; there must be an in-sight disconnect, which must remain in a line of sight (could be over 50 ft away and therefore out of sight per Art. 100) to the farthest section that can be energized. This doesn't preclude the sign wrapping around the comer of a building, and in another important clarification, the Code now covers this point by requiring that the disconnect be capable of being locked open if a sign section is out of view.
If there is an electric controller, the rules get more complicated because what was an exception to the in-sight rule is now an improperly worded second paragraph. This paragraph says that a disconnect is permitted within sight of (or in the same enclosure as) the controller, capable of being locked open. Looking at the historical context, it is clear that this is still intended as an alternative method of fulfilling the requirement. The paragraph would have no point otherwise; the Code certainly doesn't need to give permission to install an additional disconnecting means, although that is how the literal text can now be read.
Sec. 600-7. Completely new rules apply to grounding metallic sign equipment at the end of raceways enclosing secondary conductors from neon transformers. Some of these details became the subject of an appeal to the NFPA Board of Directors after the first printing of NEC was authorized. The board, however, has declined to make any changes in this section.
EC&M tip: When you are designing the layout of your secondaries, don't forget the length limitations in Sec. 600-32(j).
What happened: In addition to the usual grounding requirements for conductive enclosures (addressed in the former Sec. 600-5 and relocated here), there are very specific requirements for grounding on the secondary (high-voltage) side of the transformer.
* Metal raceways can be used, including flexible metal conduit provided it is appropriately bonded.
* Flexible nonmetallic wiring methods can be used, provided a No. 12 (min., larger if required by Table 250-95) conductor is installed on the exterior of the nonmetallic wiring method.
The actual text refers to "flexible nonmetallic tubing or conduit" but the NEC doesn't recognize flexible nonmetallic tubing as a Chapter 3 wiring method, only conduit. The text is silent on both rigid nonmetallic conduit and electrical nonmetallic tubing (ENT) as a wiring method, and that being the case, the AHJ must make the decision. ENT is not "flexible nonmetallic tubing"; it is a "pliable" raceway per Sec. 331-1. The rule should be applied to any nonmetallic conduit or tubing, for the reasons given in the background material. In addition, new Sec. 600-32(j), which covers the allowable raceway lengths as a companion change to this, applies to metallic and nonmetallic raceways generally, whether they are rigid or flexible.
Appellate issues: 1) Note that the length of the metal raceway in the initial NEC printing isn't specified. This means that the maximum length would revert to the 6-ft maximum allowed by Sec. 250-91 (b) Ex. 1, unless an equipment grounding conductor is installed in the raceway. These circuits run in the fractions of an ampere, and there is a testing lab fact-finding study showing that 100 ft of flexible metal conduit is an adequate ground return path. Although the appeal has been rejected, the practice has been proven to be safe, is widely done, and may be allowed by local codes. This doesn't affect the maximum metal raceway length of 20 ft from the transformer to the sign. This is where the principal corona problems usually arise. What it would do is allow point-to-point wiring within the sign in flexible metal conduit, with 100 ft as the maximum total rerum path.
2) An inadvertent result of the final wording of the literal text is that each individual tubing support must be bonded. There appears to be a consensus that this is excessive, however, since the appeal failed, any exceptions on this point will have to be made in local code actions.
3) The minimum No. 12 size rule on the equipment grounding conductor was not substantiated during the comment process and has been questioned. Although this now won't be changed, note that it conflicts with No. 14 allowed in Sec. 250-97.
4) The panel had suggested an exception for grounding metal parts of a listed sign with an isolated power supply or transformer secondary. The appellant thought the industry could live without this exception, and it will not be restored.
Background: Secondary conductors for signs (Type GTO) are generally unshielded, which means that if the conductor is in contact with a grounded surface the entire voltage gradient to ground will be across that contact line, instead of being distributed across the insulation generally. This creates the potential for corona discharges if the air is ionized by the steep voltage gradient. Ionized air is extremely reactive chemically, and it will degrade conductor insulation to the point of failure. The longer the metallic raceway, the greater the possibility of accumulating ionized air and the greater the opportunity for insulation damage.
Although the Code [in former Sec. 600-36(c)] has required grounded metal raceway for interior uses, former Sec. 60031(e)(4) generally held that length to 20 ft for this reason. The widespread industry practice has been to use nonmetallic wiring methods, particularly on longer runs; it worked. This procedure allows the nonmetallic wiring method in longer lengths (up to 50 ft), but with the equipment grounding conductor separated just enough so the voltage gradient is a little less steep, decreasing the possibility for corona. These considerations apply equally whether the conduit is rigid or flexible.
The reason for the less than polished language in the final wording is that the panel had rejected it, and the submitter was not from this country and somewhat unfamiliar with all the nuances of the NEC. It is in the Code because he successfully complained to the Standards Council that the panel wording was unsafe, and his comment was declared accepted as written. This is a further indication that the distinction between rigid and flexible nonmetallic wiring is unintended.
Sec. 600-23. Transformers and electronic power supplies must be listed for the intended use and identified accordingly.
Sec. 600-23(b). Transformers and electronic power supplies shall have secondary ground-fault circuit protection. There are two exceptions; first, for transformers with isolated secondaries and a maximum open circuit voltage of 7500V, and second, for transformers with an integral housing for the secondary and no field wiring on the secondary side.
Background: This is, in effect, a GFPE requirement for a very particular kind of higher voltage application, and it will result in refined fault protection for these sign transformers. The reason for the 7500V exception is that neon equipment is generally rated for that voltage to ground. The problem is on the higher voltage supplies, which depending on the location of a fault, may exceed that rating to ground.
The other problem is that electronic power supplies operate at frequencies in the 20 kHz range. This may be high enough to generate enough stray capacitive leakage current to start fires, on the order of 300 times (or more) the leakage from a conventional 60 Hz transformer. This is another major change resulting from a series of complaints, the first of which resulted in Sec. 600-7 appearing in its final form. This was not, however, affected by the outcome of the appeals.
Sec. 600-23(c). The voltage-to-ground of any output terminals in the secondary circuit must not exceed 7500V under any load condition, and the line-to-line voltage must not exceed 15,000 under similar circumstances.
This corresponds with, and tightens, the former rule in Sec. 600-32(a) which allowed an additional 1000V on test. The old rule also set, in effect, a maximum voltage-to-ground of 7500V on end-grounded transformers; this rule sets that condition on any transformer. In addition to the safety issues discussed previously, this wording harmonizes with the Canadian Code. This change also resulted from the series of complaints affecting Sec. 600-7 and Sec. 600-23(b), and may be affected by the appeals, although that seems unlikely in this case.
Sec. 600-23(d). Transformers and electronic power supplies must not have a secondary current rating higher than 300mA.
This rule was based on former Sec. 600-32(b), but has been changed extensively.
* The old restriction to 4500VA has disappeared. Note, however, that 15,000V x 0.3A = 4500VA. The important safety parameter isn't actually the available power, but rather the safe current. The distinction between signs, which had a VA parameter, and outline lighting, based on 60mA has disappeared, as has the reference to 5000V core-and-coil-type transformers. Now it's just one very simple requirement.
Sec. 600-23(e). Transformer secondary "outputs" must not be connected in parallel or in series.
This used to be Sec. 600-32(d), except there were two elaborate exceptions. Both exceptions have been deleted. In addition, the former wording referred to "windings." This change still allows a midpoint ground, but within the listed transformer and not done in the field. Furthermore, in using electronic power supplies, the assumptions that used to apply to transformers in series are no longer valid. Now you must go out and get the appropriate product, and not attempt to create it in the field.
Sec. 600-32. This section covers neon sign conductors over 1000V. It is based on the old Sec. 600-31, but with very significant changes.
* (a) The rule covering allowable wiring methods for these secondary conductors has been expanded. A new rule reiterates Sec. 250-58 (a) and forbids using metal parts of a building as a grounded or equipment grounding conductor.
Essentially any Chapter 3 raceway can now be used for this, including nonmetallic varieties. This is broader than the general methods in the old Sec. 600-31(a), and a big change from the "grounded metal raceway" rule that was in old Sec. 600-36(c) for interior applications. In addition to Chapter 3 wiring methods, the new wording also recognizes "other equipment listed for the purpose." There is no blanket recognition of glass sleeving or equivalent protection, such as in the former Sec. 600-36(c) Ex. This material can still be used, but only if expressly listed. High-frequency electronic power supplies in particular will react with glass containing metallic impurities, and the AHJ must be able to verify the quality through the listing process.
Only one conductor shall be installed per length of conduit or tubing. Although the old Code hinted at this in old Sec. 600-31(e)(4), this is essentially a new rule. Note that one additional conductor can be installed, an equipment grounding conductor. If done, this would conflict with the new requirement in Sec. 600-7 to route the equipment grounding conductor on the outside of a nonmetallic raceway. Since this is permission and not a requirement, it would be best to continue to observe Sec. 600-7, but review the discussion at Sec. 600-7 and Sec. 600-32(j) below with the AHJ and decide.
Appellate issue: The panel action included an additional requirement, removed by the Standards Council, that "electronic power supplies used with metal conduit shall have the conductor protected by sleeving listed for the purpose." Although an appeal on this failed, there is an emerging consensus that GTO cable used with electronic power supplies and laying on the wall of a metallic raceway will not work properly and may fail. Some believe removing the sleeving requirement was a sub rosa effort by transformer manufacturers to discredit their electronic competition through field failures.
* (b) The allowable conductor size did not stay at No. 14, but went down to No. 18. This is a similar change as the one in Sec. 600-31. The conductors must also be listed for the purpose, rated for the voltage, and have a temperature rating not less than 105 [degrees] C. This is because electrode terminals operate as high as 100 [degrees] C. Note that even though the basis for the 105 [degrees] C insulation rating is the electrode temperature, the literal wording of existing test lab restrictions on nonmetallic wiring methods may partially preclude their use to enclose conductors with this high a rating. These restrictions would appear to have little technical validity for conductors carrying currents measured in milliamperes, but again, the AHJ needs to be consulted.
* (c) This is a new rule calling for care so conductors don't fail within the conduit. The secondary conductors must be properly handled to avoid damage.
* (d) Avoid sharp bends when pulling and dressing the cable.
* (e) Conductors must be separated from each other and the surface wired over by at least 1 1/2 in.
This is the same as former Sec. 600-31(d), but only figured at one, the highest, possible voltage. The previous allowance to use a 1-in. separation for 10kV and less was not carried forward.
* (f) Insulators and bushings (for conductors) must be listed for the purpose. This was in old Sec. 600-31 (d), last sentence.
* (g) Conductors emerging from raceways must extend 4-in. if in a damp or wet location and 2 1/2 in. in a dry location. This was old Sec. 600-31(e), in a much more complicated format based on circuit voltages. As in other cases the new rules have been written around the worst case voltage (15kV).
* (h) Grounding the midpoint, etc. This part of the rule did not change. It used to be Sec. 600-31 (g).
* (i) No circuits over 1000V in dwellings. This has been around in Sec. 410-80(b) for some time, meaning these circuits couldn't be used for lighting in dwelling occupancies. Now this portion of the Code includes a similar rule.
Sec. 600-32(j). This subsection is new and sets maximum lengths on raceways enclosing transformer secondary conductors.
The upper limit is a 20-ft maximum for metal raceways and 50 ft for nonmetallic raceways. This change also resulted from the series of complaints affecting Sec. 600-7, and Sec. 600-23(b), and 600-23(c). Please refer to the drawing and discussion at Sec. 600-7, on page 42, for more information. Although potentially affected by the appeals as well, there is a consensus on this and indeed, it was not disturbed by the NFPA Board of Directors.
Note that Sec. 600-7 requires (depending on the disposition of the appeal) the equipment grounding conductor to run on the outside of nonmetallic raceway. Sec. 250-79(f) requires bonding conductors to run on the inside of a raceway if longer than 6 ft. This means, in effect, that Sec. 600-7 must be taken as a modification (see Sec. 90-3) of Sec. 250-79(f) in so far as the maximum length is concerned. Putting the equipment grounding conductor inside the raceway defeats the purpose for allowing a longer length of nonmetallic raceway in the first place. The other requirements in Art. 250 concerning routing with the raceway, and general requirements about protecting conductors generally, will still be enforceable.
Sec. 620-13. The rules for sizing elevator motors now agree with the rules in Art. 430 for comparable motor installations.
What happened: This section has been completely rewritten. The following specific areas have been changed:
* The section implicitly recognizes throughout that these motors, although continuous-rated, are classified in terms of duty cycle as intermittent duty by Sec. 620-61(b)(1). In accordance with Sec. 430-22(a) Ex. 1, the motor nameplates must be used in calculations, not the standard values in Table 430-150, etc. This is a different procedure than the usual process of only using nameplates to size running overload protection. These motors need not be supplied with separate running overload protection, per Sec. 430-33.
* Former Sec. 620-14 on adjustable speed drive equipment has been folded into this section. The rules for a single motor supplied in this way are in Sec. 620-13 (b) and (c), and multimotor calculations are in Sec. 620-13(d).
* In accordance with Sec. 430-24 Ex. 1, on a feeder calculation for a group of motors, the ampere ratings for elevator motor loads (figured as intermittent) used in a summation is now the largest result from the Table 430-22(a) Ex. calculations, without imposing an additional 25%.
Background: If there were other motors on the feeder that weren't in duty cycle service, then they (at 125%) would be compared with the elevator motors to determine the highest rated motor. The final ampacity is the sum of all full-load currents plus 25% of the highest rated motor, but only if a continuous-duty motor at 125% ends up as the highest load. For example, referring to the drawing, suppose a second motor rated 40 hp (but not an elevator load) were added. By Table 430-150, this is figured as 52A, and 1.25 x 52 = 65A. The 40-hp elevator motor would still be the largest motor because as figured from Table 430-22 (a) Ex., (52A x 1.4 = 73A) it's larger than the conventional motor, even with the extra 25%.
For some time, there have been three different calculation procedures in the Code for loads such as these. This section used to call for 125% of the largest motor plus the other motors. In the case in the drawing, that would be 265A. Since this section is in Chapter 6, it technically overruled Sec. 430-24 Ex. 1 for elevator motors. Meanwhile, Chapter 9, Example 9 cited Art. 430 while applying an additional 25% to the Table 430-22(a) Ex. results, for a total of [1.25 x 1.4 x 52A + 5 x 1.4 x 40A] 371A.
Thus we had the technically correct way in Art. 430 (353A prior to applying demand factors), which could not literally apply because of Sec. 90-3; we had Sec. 620-13, which was completely wrong technically (265A at the same point) but which did apply; and we had Chapter 9 Example 9 mentioning the appropriate rules in Art. 430 but using them incorrectly (for a result of 371A before demand factors were applied).
The motors in the drawing are based on Example 9. The examples have now been rewritten in accordance with Sec. 430-24 Ex. 1, and the result is that all three areas in the Code now are in full agreement as to how to make these calculations. Agreement, that is, on motor calculations. There may be a new area of disagreement for adjustable speed drive systems, however. Sec. 430-22(a) now has a new Ex. 3 calling for conductors to be sized at 125% of the conversion equipment rating. In this case Art. 430 appears to be incorrect because there was no substantiation supporting that 125% factor on motors being used for duty cycle applications. Remember, you can't apply one exception [Sec. 430-22(a) Ex. 1] to another (Ex. 3). For elevators, however, you need not go beyond this section because of Sec. 90-3.
Sec. 620-23 and 24. Two new sections cover machinery room/machinery space lighting and receptacles, and similar outlets in hoistway pits.
* (a) A separate branch circuit must supply the lighting and receptacle(s) in each area. This required lighting must not be connected to the "load side terminals of ground-fault circuit-interrupter receptacle(s)."
* (b) The light switch must be at the point of entry into the machinery space or at the hoistway pit access door, as appropriate.
* (c) At least one 125V single phase duplex receptacle must be provided in each room (or space).
* New FPNs refers the user to the Safety Code for Elevators and Escalators for required illumination levels.
This correlates with Canadian requirements. Note that the amperage rating of the receptacle isn't specified, and that, on the literal text, two single receptacles or a triplex receptacle wouldn't be acceptable. It would be acceptable, perhaps unintended unless on a separate branch circuit, to connect the lighting to a GFCI circuit breaker or a GFCI trip unit that mounts in an outlet box but has no receptacle slots. Although somewhat unclear, the rule does not appear to prohibit multiple branch circuits serving such spaces, provided they do not serve other spaces. The standard referred to in the FPNs sets minimum illumination levels at the floor of 10 foot-candles in machinery spaces and 5 foot candles in the hoistway pit.
Sec. 620-51. This section on disconnecting means has been completely reorganized into four subsections. The parent language now includes the requirement in Sec. 430-103 that no single pole of the disconnect be able to operate independently. A new paragraph requires that the disconnecting means for the main power supply conductors must not open the branch circuits required in Sec. 620-22, -23, and 24.
Each subsection has important changes.
Sec. 620-51 (a) The disconnecting means can be a fused motor circuit switch or a circuit breaker arranged so as to be capable of being locked in the open position. It must now be a listed device.
The old wording "arranged to be locked" literally required the disconnect to be routinely locked in the open position. The former second paragraph on selective coordination never belonged in this section and has been relocated to Sec. 620-62.
Sec. 620-51 (b) A new subsection titled "Operation" clarifies, once and for all, the intent of the 1993 rule change [ILLUSTRATION FOR DRAWING OMITTED] in the event sprinklers are located in the hoistway or in machinery spaces. The disconnecting means must not be opened or closed from "any other part of the premises," such as by a shunt trip activated from a remote part of the building. If opened, it must not be automatically closed, only manually.
This should settle the questions that arose as to the intent of the 1993 revision. This language specifically includes the machinery space in the scope of the requirement. A water discharge onto an elevator with live circuits and still carrying passengers can be extremely hazardous, as the brakes can slip, and the control circuits could fail. A new FPN reinforces this intent. After the car is parked and disconnected with the passengers discharged, waterflow to the sprinkler can be allowed safely.
Sec. 620-51 (c). Disconnects must be located where readily accessible to qualified persons.
* (1) On elevators without generator field control, the disconnecting means must be in sight of the motor controller. If a driving machine or a motion or operation controller is out of sight of this disconnect, additional manually-operated switches, wired into the control circuits, must be provided adjacent to such equipment. A new second paragraph requires a single disconnecting means that can be locked open for a driver motor in a remote machinery space.
* (2) On elevators with generator field control, the same series of changes was made, except referring to either the driving motor or the motor-generator set being in a remote machinery space.
* (3) On escalators and moving walks...(no changes).
* (4) On stairway and wheelchair lifts, the allowance for the disconnect to be in the same enclosure as the motor controller has been deleted.
It remains in Sec. 620-71(a) in a qualified form.
Sec. 620-51(d). A new subsection addresses required identification of disconnecting means in elevator machine rooms, which must be by identifying number of the driving machine they control. The disconnecting means must now also be provided with a sign giving the location of the supply-side overcurrent device.
This allows service personnel, who may be far more familiar with the elevator than the building, a better chance at locating a remote device if it has tripped open, stranding passengers between floors. Although there is a selective coordination rule, that is irrelevant if there is a fault in the feeder ahead of the machine room.
Sec. 620-62. If more than one driving machine disconnecting means is supplied by a single feeder, the overcurrent devices in each disconnecting means shall be selectively coordinated with any other supply side overcurrent protective devices.
This used to be part of Sec. 620-51 (a), but has been relocated to Part G of the article on overcurrent protection which is more appropriate. This rule, for the first time, is conditioned on the feeder supplying more than one overcurrent device(s). This gives relief on small installations where each fused switch in the machine room is on its own circuit from a switchboard. Selectively coordinating two equal sized devices is impractical, and has led to artificial oversizing on the feeder.
Sec. 620-85. Elevator service receptacles must be GFCI receptacles only; upstream protection is not allowed.
What happened: The GFCI requirement for elevator service receptacles:
* Expanded to cover receptacles in escalator and moving walk wellways, in addition to machine rooms, machinery spaces, pits, and elevator car tops;
* In general, can only be satisfied by using a GFCI receptacle, but;
* In a machine room, remote GFCI protection is permitted.
* For a single receptacle only, installed for a permanently installed sump pump in a pit, the GFCI requirement can be waived using a new exception.
Background: This change requires that the GFCI protection be provided at the point where it is being used. If it trips, the service personnel will be almost, if not completely in reach of the reset button. This avoids subjecting a technician to a greater risk of injury, i.e climbing off the elevator car top in order to reset a tripped device. The new exception is similar to the allowances that have been given similar equipment in Sec. 210-8(a).
Art. 625. A new article has been added to cover electric vehicle charging equipment. [ILLUSTRATION FOR DIAGRAM OMITTED]
What happened: The scope for this new article was carefully drawn. It covers the following topics:
* Electrical conductors and equipment external to an electric vehicle that connect an electric vehicle to a supply of electricity by conductive or inductive means;
* Installation of equipment and devices related to electric vehicle charging.
Note that the conductors and equipment covered are external to the vehicle. The vehicle will be covered by other standards, and automotive vehicle wiring isn't covered in the NEC per Sec. 90-2(b)(1). Note also, that the power connection can be by conductive or inductive means. Some charging methods use an inductive paddle that uses ac current fluctuations to induce a charge in the vehicle. The result is no exposed conductive parts at any time, which eliminates the shock hazard. The article also covers related equipment and devices, although none on the vehicle itself.
Background: Many regions of the country with air-quality problems are either close to or have mandated a partial conversion to zero emission vehicles, meaning electric vehicles. The electric utilities, figuring the majority of charging will take place at night during their slack periods, see this as a way to strongly improve revenue without adding much in the way of new plant. In fact, some utility projections show this as the largest single household electrical load in the years ahead. These two forces have converged to produce this new article. Some of the more important requirements follow:
Sec. 625-2. Definitions. There are four terms defined in this section.
* Electric Vehicle. This definition separates traditional highway uses from golf carts, airline ground transport, etc. Off road vehicles, such as industrial fork-lift trucks, etc., are not within the scope of this new article.
* Electric Vehicle Connector. This clearly allows for either a conductive or an inductive charging connection.
* Electric Vehicle Nonvented Storage Battery. These are hermetically sealed. A major issue is the release of hydrogen during charging; these batteries can be treated quite differently than conventional batteries in this regard.
* Electric Vehicle Supply Equipment. This is the equipment installed specifically for delivering energy to the vehicle.
Sec. 625-14. Rating. This must be high enough for the load to be served, and must be considered as continuous. Although some highway quick-charge protocols assume a 10- or 15-min. recharge at very high ampere values, the rule is for a continuous classification on any load.
Sec. 625-22. Ground-Fault Protection for Personnel. The electric vehicle supply system must incorporate shock protection that may differ somewhat in trip thresholds from conventional GFCI levels, but that operates on same principle. The wording of this section is carefully chosen to echo the definition in Art. 100 of GFCI, while not using the actual term. This is exactly as intended; the test labs and manufacturers are being given some design flexibility here. If the charging equipment is cord- and plug-connected, then this function must be built into the attachment plug or into the supply cord within a foot of the plug.
Sec. 625-23. Disconnecting Means. High-capacity charging equipment (over 60A or over 150V to ground) must have a disconnecting means in a readily accessible location. It must be able to be locked in the open position. This is a disconnecting means for the equipment, and therefore a unit switch in the equipment would not comply, even if it opened all ungrounded conductors. Maintenance personnel must be free to service the entire unit without hazard.
Note that this equipment would meet the definition of an appliance (other than industrial, produced in standard sizes, etc.) and therefore must comply with Sec. 422-21(b). That rule also requires a local disconnect, which can only be the branch-circuit protective device if it is within sight or can be locked open. These provisions can be enforced on any capacity charging system.
Sec. 625-29. Indoor sites. These sites include both attached and detached residential garages, enclosed and underground parking "structures," agricultural buildings, etc. The charging equipment must be located so the charging cable can connect directly to the vehicle. Unless listed differently, the vehicle coupling means must be stored or located within a zone between 18 and 48 in. above the parking surface. Strict ventilation requirements apply.
What happened: One of the key aspects of the new article is in the area of ventilation. Mechanical ventilation as covered in Subsection (c) must be provided. It must be permanently installed, and it must include both supply and exhaust equipment arranged to take air from and exhaust air directly out to the outdoors. This ventilation must be interlocked with the charging system, and it must operate during the entire charging cycle. The required volume of air to be exchanged, in cfm, is provided in a new table based on the ampere rating and voltage of the branch circuit supplying the charging equipment. For example, a 20A 120V supply requires 49 cfm, and a 200A 480V 3-phase supply requires 3416 cfm. These numbers apply for each space equipped to charge an electric vehicle. If there are two spaces, then the required ventilation doubles. The electric vehicle supply equipment receptacles or power outlets must be clearly marked: For Use With All Electric Vehicles.
There are two variations on this requirement. One is for nonvented storage batteries. If these batteries are being used, or where the vehicle is listed or labeled as suitable to be charged indoors, mechanical ventilation isn't required. In this case, the receptacle or power outlet supplying the charging equipment, and the charging equipment itself, must be clearly marked: For Use Only With Electric Vehicles Not Requiring Ventilation.
The other variation is for 15A and 20A 125V receptacles. An exception allows these receptacles to supply power to charging equipment without the charging equipment being interlocked with a ventilation system, provided the receptacle is so interlocked. The receptacle must be switched, and the mechanical ventilation system must be interlocked through the switch feeding the receptacle. The switched receptacle must be marked: For Use With Electric Vehicles.
EC&M tip: Note that per testing lab listing restrictions, conventional two-pole snap switches are for single circuit use only unless tested and marked for use on more than one circuit. As of this writing none have been so tested and marked.
Background: Under current technology the majority of battery charging involves the release of hydrogen gas. This is a Class I Group B gas, extremely dangerous, and its lower explosive limit is only 4%. That means that a hydrogen-air mixture over 4% hydrogen by volume can explode. Although hydrogen is much less dense than air and dissipates rapidly, charging operations generate enormous quantities. Actual testing showed ignitable concentrations of hydrogen near the ceiling even on 15A branch circuits in residential garages with the door open! The mechanical ventilation requirements in this section need to be taken seriously.
Sec. 680-4. The definitions of permanently installed and storable pools have been changed to eliminate the maximum horizontal size parameter for storable pools.
What happened: The former dimension limit on storable pools was for a maximum size of 18 ft and a maximum wall height of 42 in., along with a condition calling for such pools to be capable of ready disassembly for storage and reassembly for subsequent use. The 18-ft limitation has been removed. In addition, the new wording includes a restriction that the pool be constructed "on or above the ground." Finally, instead of referring to a wall height of 42 in., the new wording uses 42 in. as the maximum water depth. This may increase the vertical size of these pools somewhat. The definition leaves unchanged the provision for inflatable pools being classed as storable regardless of dimensions.
Background: The change leaves an objective measurement (42 in.) in the NEC, which is vital for consistent enforcement by the inspection community. It broadens the flexibility of manufacturers that make these pools. The change resulted from a panel task group study of what kinds of pools would be routinely removed after each swimming season, and which would not. The pools that require special site preparation and large liners that would probably be damaged by shrinkage if disassembled and stored are those for water depths deeper than 42 in. Those are permanent pools. On the other hand, most pools larger than 18 ft but with water no deeper than 42 in. are still designed for ready disassembly and storage.
Sec. 680-12. A disconnecting means is now intended to be placed within sight of pool, spa, and hot tub equipment.
EC&M tip: Check with the AHJ to see how this "rule" will be interpreted, because it isn't correctly worded. It covers many unintended items, but can even be plausibly interpreted as not mandatory in certain key aspects.
What happened: A new Sec. 680-12 has been located in Part A so as to apply as appropriate to all spas, pools, and hot tubs throughout the article including spas in health care facilities. It says that "disconnecting means shall be accessible" (but without requiring that they be installed if, for lack of any applicable Code requirement, they would not otherwise have been installed) "located within sight from pool, spa, and hot tub equipment" (including in-pool lights and all other equipment, not just motor loads) "and shall be located at least 5 feet horizontally from the inside walls of the pool, spa, or hot tub."
Background: This change, if enforceable as intended, will make it more convenient for owners of outdoor pools, spas, and hot tubs to have them serviced by outside contractors; now those contractors won't have to make an appointment so as to be sure to have access to disconnecting means already required by the Code but perhaps located in the basement. Otherwise, these service personnel have tended to work the equipment hot.
Note that other sections of the NEC already require in-sight disconnecting means of motor loads, unless the controller is remote (relatively unusual although not unknown in these cases). Heating equipment, if on a separate branch circuit from the motors, would certainly be affected [Sec. 422-21(b) allows a lock-out on the circuit-breaker], as would pool lighting (certainly not intended). Whether this kind of requirement is consistent with Sec. 90-1(b) is another question, since the minimum safety issues have long been addressed elsewhere in the NEC.
Sec. 680-20(b)(1). This section has been changed to allow liquidtight flexible nonmetallic conduit to be run to a wet-niche or no-niche fixture from the swimming pool junction box, however that allowance is of no effect due to a correlation error.
"Liquidtight flexible nonmetallic conduit" has been added to the second paragraph, and the fourth paragraph now reads "a nonmetallic conduit." There was no appropriate technical substantiation for this change; only the unproven assertion that liquidtight flexible nonmetallic conduit (which is being listed for below grade use) "is a safe wiring method for this application." Note, however, that Sec. 680-25(b)(1) does not recognize this wiring method, which effectively nullifies this change.
Sec. 680-22(a). A new exception (No. 4) exempts listed double-insulated (DI) equipment from the bonding requirements around permanently installed pools, provided the internal dead metal parts of such equipment are provided with a means for grounding.
What happened: The new exception requires listed DI equipment in the vicinity of a permanently installed pool to not be bonded; the DI equipment must provide a means for grounding the internal noncurrent-carrying metal parts.
Background: Part C of the article covering storable pools has recognized this concept for some time in Sec. 680-30, where these internal parts of DI motors are connected to an equipment grounding conductor. That is entirely appropriate in the context of storable pools that have no bonding requirement in the first place. However, this change correlates with the new Sec. 680-28 recognizing such motors at permanently installed pools, both above and in-ground.
These pools will continue to have an extensive bonding grid [ILLUSTRATION FOR DRAWING OMITTED]. Historically that bonding grid has been connected to the equipment grounding system for the premises through the required bonding connection to the recirculating pump motor (and, if used, the forming shells to wet-niche fixtures). Many pools don't have in-pool lights. That didn't matter as long as there was a pump bonded to the grid, which was always the case.
Now that is no longer the case. For the first time in the 100-yr history of the NEC, we have an extensive bonding grid with the real possibility of no conductive reference to an equipment grounding system. It is true that the bonding grid was never intended as an equipment grounding return path. Its true intent was, and is, the reduction of voltage gradients for swimmers. Nevertheless, there is a real possibility for potential differences between grounded electric equipment brought into the pool area while connected to a receptacle in the pool area, typically the one required by Sec. 680-6(a)(2).
Sec. 680-25(c) Ex. 3. The intended application of this exception to Type NM cable has been clarified by referring to an equipment grounding conductor "that is insulated or covered by the outer sheath of the wiring method."
Previously the exception referred to "an insulated or covered equipment grounding conductor." A covered conductor is defined in Art. 100 as one "encased within material of composition and thickness that is not recognized by the Code as electrical insulation." Although the jacket of Type NM cable covers the bare equipment grounding conductor in the dictionary sense, but does not strictly "encase" it as described in Art. 100, some had argued that Type NM cable could not be used as the wiring method for a swimming pool motor in the interior of a one-family dwelling.
This exception originated in the 1987 NEC intended for one principal purpose, namely, to allow Type NM cable in one-family dwellings for these motors. It has been changed in every single subsequent code cycle with the same objective, and yet every previous version of this exception has allowed some to argue that Type NM cable wasn't really included. This language should finally end the controversy.
Sec. 680-28. A new section permits double-insulated pool pumps at permanently installed pools.
They must incorporate an approved system of double insulation and also have a grounding means for the inaccessible dead metal parts. These motors would be like those allowed in Part C for storable pools, except that in this case the cords would have to comply with Sec. 680-7 and not exceed 3 ft, instead of the 25-ft cords customarily allowed by listing procedures for the inherently temporary, storable pools. Please refer to the discussion on Sec. 680-22(a) Ex. 4 for a full analysis of the implications of this change.
Sec. 680-41 (e). The bonding conductor at an indoor spa or hot tub need no longer be a solid conductor.
This changed because during the proposal stage the panel decided to remove the requirement for solid bonding conductors in Sec. 680-22(b), and this changed to agree with that action. Then, after overwhelming public comment against the change in Sec. 680-22(b), that change was rejected, but this didn't change back with it. In fairness, the likelihood of damage from corrosion is typically much greater in Sec. 680-22(b) environments.
Sec. 680-42. A new exception allows omission of GFCI protection for an outlet that supplies a listed serf contained spa or hot tub, or a listed spa or hat tub equipment assembly, in cases where the product has been marked to indicate that integral GFCI protection has been provided for all electric parts within the spa or hot tub, or within the equipment assembly as applicable.
A FPN has been added as well, referring to the new definitions of these terms in Sec. 680-4.
Sec. 680-60. This section (and thereby all of Part F) now includes "pools and tubs for therapeutic use in health care facilities, gymnasiums, athletic training rooms, and similar areas." To correlate with this, the title of Part F now reads "F. Pools and Tubs for Therapeutic Use."
The hazards associated with this equipment must be factored into the appropriate code provisions whether or not the tub in question is in a health care facility. This change recognizes similar equipment in other locations.
Sec. 680-70. All 125V single-phase receptacles within 5 ft of the "inside walls of a hydromassage tub" must now be GFCI protected.
This covers the increasingly common practice of locating hydromassage bathtubs (note that is the correct term, not "tub") outside of bathrooms and within other living spaces, such as master bedrooms. Note that the Code doesn't specify how the 5-ft dimension is to be measured. For example, if it is measured according to Sec. 680-6(a) FPN, then it does not extend through a doorway. If it is measured according to Sec. 680-41(a) FPN it does extend through a doorway. In neither case does it extend through a wall.
The Code also doesn't clarify whether this applies to any receptacles in a 5-ft horizontal radius, or whether, for example, a receptacle just outside the tub enclosure and 5 1/2 ft above the tub walls is exempt from the rule. Although the horizontal radius makes common sense, the panel just rejected a proposal to add the word "horizontal" to Sec. 680-41 (a)! The stated reason for rejecting that proposal was: "The horizontal measurement on receptacles that are normally mounted at or near ground level is not as critical as switches, lights and similar devices that are mounted at a higher plane from the spa level." Not so critical, of course, unless the receptacle is at counter height, as is quite common, or in a wall-mounted fixture; then what?
Since the Code is silent on how the 5-ft rule should be measured, you will need to have the AHJ make an interpretation. Clearly the most appropriate way to apply the rule (and the way least likely to cause legal difficulties later on) is horizontally, and along the path of any cord even through open doorways. Note also, however, that this requirement does not extend beyond the 5-ft radius, except in bathrooms where all receptacles are covered by a different rule in Sec. 210-8. This differs from the rule for hot tubs and spas, which extends to 10 ft (with receptacles excluded from the first 5 ft of that radius).
Sec. 690-31. A new subsection (c) and Table 690-31(c) on ampacity correction factors covers the use of flexible cords and cables for connecting moving parts of tracking photovoltaic modules. Such cords must meet the following requirements:
* Hard service cord or portable power cable
* Comply with Art. 400 and be identified as for extra-hard usage
* Be listed for outdoor use
* Be listed as resistant to both sunlight and water
The ampacities are covered in Tables 400-5A and 400-5B. The new table covers derating of cords at higher than 30 [degrees] C ambients by using the adjustment factors now in Table 310-16, except that a 105 [degrees] C column has been added because cords with that temperature rating is made. Note the listing condition for water resistance. This is for continued exposure to water, as is required for cord-connected equipment sitting in fountains. The usual "W-A" or "Outdoor" classification does not meet this requirement.
Sec. 690-71. A new subsection "(c) Current Limiting." now requires a "listed current-limiting overcurrent device" to be installed "in each circuit adjacent to the batteries where the available short-circuit current from a battery or battery bank exceeds the interrupting or withstand ratings of other equipment in that circuit."
If fuses are used, the installation must also comply with Sec. 690-16, which requires fuse disconnectability from all sources of supply if accessible to other than qualified persons. Note that the phrase "interrupting or withstand ratings" may be incorrect. "Interrupting" should apply only to available currents that would be broken at fault levels, per Sec. 110-9. A 15A-rated snap switch need not be protected from fault currents above that level. In addition, the word "withstand" is in reference to continued routine functioning of equipment, and is a higher standard of protection than is generally considered appropriate for a Code rule addressing minimum safety requirements.
Art. 695. A new article has been accepted to cover the unique wiring characteristics appropriate for fire pumps.
The most important material follows:
Sec. 695-3. The fire pump must be connected to either a utility source or to an on-site production source, both arranged to minimize the possibility of damage by fire. If a tap is made ahead of the service disconnecting means, that tap must not be in the same compartment as the service disconnecting means. The power source must directly connect the power source ta a listed fire pump controller, except under carefully controlled conditions. Those conditions assure that the disconnect will not be inadvertently opened.
Background: This section is perhaps the most controversial of all the various fire pump requirements because it makes no provision for double-ended substations with provisions for automatic throw-over and all the other highly reliable means that have been developed by qualified electrical engineers over generations of work on the problems of assuring highly reliable power. Instead you are obliged to serve the pump directly, or almost directly from the source, as shown in the drawing.
This makes it virtually impossible to install a fire pump on the usual industrial or other campus-style distribution systems with buildings fed on double ended loops from other buildings, which are in turn from yet other buildings, etc. You will need to try and sort this out with the AHJ at the local level. The Fire Pump Committee, which is responsible for this material, simply refused to recognize countervailing experience. Although the Code Making Panel recommended such provisions, they were overturned later in the process. Although the Code allows for a generator in Sec. 695-4, it is only in addition to one of the recognized principal supplies, and does not legitimize a remote connection to a feeder as the principal source.
The provisions in the exception about assuring the disconnect remains on is rooted in human, not electrical behavior. The concern is with firefighters deciding to disconnect the building and ending up opening every service switch including the fire pump disconnect.
Sec. 695-4. If the AHJ decides the primary source of power is unreliable, then an additional source is required, which can be an on-site generator. The generator must be large enough to allow instantaneous pickup of the fire pump load.
The sources must be arranged so a fire at one won't disrupt the other. The generator size and the overcurrent protection, etc. does not have to meet the normal locked-rotor capacity parameters as other portions of the rule. The idea is that two somewhat unreliable sources are an acceptable trade-off for one highly reliable source.
Sec. 695-5. Transformers in a fire pump circuit must be load rated for 125% of the full fire pump load (with any associated loads). The primary protection must carry locked-rotor currents indefinitely, and secondary protection isn't allowed.
The fire pump must be allowed to run to failure. The same concept is in Sec. 695-8(c), where conductors are protected against short circuit but not overload.
Sec. 695-8. Power Wiring. The first choice on power wiring is to route the conductors outside the building as service conductors, or, failing that, route them inside the building under the provisions of Sec. 230-6, where a 2-in. concrete encasement substitutes for being outside the building. The other possibility, for wiring with overcurrent protection, is to run the conductors in the building in a "listed electrical circuit protective system" with a minimum 1-hr fire resistance rating.
There are several protective concepts at play here, and it is very important to understand how they interrelate. The rules in Art. 230 protect the building from the conductors. That's why they don't come in the building, unless encased in masonry. Sec. 695-8(a) incorporates that concept. An electrical circuit protective system protects the conductors from the building. These systems are designed to make certain that the conductor insulation holds up and the enclosed circuits can continue to perform for the prescribed time period in a fire. Sec. 695-8(a) Ex. incorporates this concept, which only applies on the load side of an overcurrent protective device.
These systems are listed in the UL Building Materials Directory under that heading. There are very few such systems that would apply here, including a special wrap for 2-in. and larger rigid steel conduit. Type MI cable qualifies if you observe special additional provisions beyond the NEC rules in Art. 330, including special support rules for every 3-ft of cable, and a provision that all terminating seals be at least 1 ft into a protected area. None of these systems involves various steel beam encapsulating sprays. Those spray-on compounds are designed to prevent steel framing from softening at approximately the 1000 [degrees] F mark; they are absolutely worthless as far as helping assure the survival of conductor insulation.
There are also some specific wiring method requirements in this section that you shouldn't lose track of. In Sec. 695-8(b), the wiring between a fire-pump controller and the pump is restricted to one of just four wiring methods: rigid metal, intermediate metal, and liquidtight flexible metal conduit, and Type MI cable. The same wiring methods are all that's available for the control wiring as well, per Sec. 695-9(e).
Sec. 695-8(d) prohibits using the fire pump controller as a junction point for nonfire pump loads, and jockey pumps shall not be connected at this point either. Finally, Sec. 695-8(e) sets a voltage drop limitation on the fire pump feeder or service wiring: 5% while running at 115% of rated load current, and not over 15% while starting. The reason for this is not the pump so much as it is the possibility that the magnetic contactor in the starter would chatter under such a low voltage. That, in turn, is why the exception exempts this requirement during manual starting.
Sec. 700-9(b) Ex. 1. A new sentence requires that an emergency system transfer switch must supply only emergency loads.
What happened: The main rule calls for a complete separation between the emergency system wiring and all other wiring, but the first exception simply said "In transfer equipment enclosures." That left open the question of, in effect, where in the transfer switch could the foreign systems be connected. An additional sentence at the end of the exception has been added to help answer this question. "The transfer equipment shall supply only emergency loads."
Background: A perennial question has been whether an emergency system transfer switch could be used to supply both emergency and normal standby loads, and this exception has been the focus of that debate. Clearly the exception allowed both normal and emergency conductors within it, the question was where, and for what purpose? The intent has always been obvious in part. Obviously you can't have a transfer switch without both systems present on the line terminals to which the switch transfers load.
The real question was whether both load branches could originate on the load terminals of the same switch. Many distribution systems have been designed with the load terminals of a transfer switch arranged in just this way. The engineer allows for complete emergency/nonemergency system separation from the transfer switch out, meaning that the only potential issue was within the switch itself. This exception was then cited as the basis for allowing both loads on the single switch. This has now been clarified as improper. The reason is to increase the reliability of the emergency system by preventing faults on optional standby systems from affecting it.
Note that this provision partly conflicts with Sec. 517-30(b)(4), which for small hospitals allows a single transfer switch for the entire essential electrical system (where not over 150 kVA). The essential electrical system of a hospital is, per Sec. 517-30(b)(1), comprised of an emergency system and the equipment system. Per Sec. 517-30(c)(1) (final paragraph), the equipment system need not be divorced from other load circuits, just like other standby loads generally. Therefore, to the extent that small system supplies the equipment system, it is supplying nonemergency load. There really isn't anything wrong with the limited allowances in Art. 517, but since Chapters 5 and 7 have equal rank under Sec. 90-3, some correlation needs to be done.
Sec. 700-9. A new subsection (c) requires enhanced protection of emergency systems in higher hazard occupancies, including high-rise buildings and large places of assembly.
What happened: In all assembly occupancies over 1000 persons, and in most high-rise buildings (over 75 ft high), that is, those high-rise buildings with any of the following occupancy classes: Assembly, Educational, Residential, Business, Mercantile, or Detention and Correctional, special separation rules apply to the feeders and to the distribution equipment.
The emergency system feeders and the distribution equipment including transfer switches must be either fully protected by automatic fire suppression, or run in an electrical circuit protective system with a minimum 1-hr rating. The requirement for sprinkler protection is for the feeder, not the building. The fact that the building is fully sprinklered in accordance with a local building code does not necessarily mean that this rule is met. If the feeder goes up a chase, then automatic fire suppression must be in that chase. Otherwise the emergency system feeder could be the first casualty of the fire.
If the sprinkler option doesn't work, then the other option is the electrical circuit protective system. As noted in the discussion of new Sec. 695-8, these systems are designed to make certain that the conductor insulation holds up and the enclosed circuits can continue to perform for the prescribed time period in a fire. They are not steel-beam encapsulating sprays.
Background: There have been many efforts to increase the survivability of emergency circuits in different states around the country, and now the NEC is following suit. These efforts followed actual examples of loss experience, where large (usually high-rise) buildings were evacuated with candles and cigarette lighters after the failure of an emergency system.
There is a major problem with the options presented, however. There is no option to isolate the feeder circuits by construction techniques. Even if a feeder were embedded in concrete, or surrounded with enough gypsum board to achieve a 1-hr fire separation, that is not one of the options in this new rule. Be sure to discuss this with the AHJ to see what your options will be, and whether some relief would be entertained under Sec. 90-4. There is a general consensus that this rule ended up unintentionally strict, but the problems came to light too late in the process to correct.
Sec. 700-12. A new fourth paragraph adds similar protection rules for emergency generation equipment as have been added for feeders and distribution equipment in Sec. 700-9(c).
This correlates with Sec. 700-9(c), requiring the generator room to be either sprinklered or a "space(s) with a one (1) hour fire rating." In the case of a generator room, the separation/sprinkler option is realistic.
Sec. 700-12. Former subsection (e), allowing a tap ahead of the service disconnect as an emergency system source "where acceptable to the authority having jurisdiction" has been deleted.
What happened: The long-standing permission for an AHJ to allow a tap ahead of the service disconnect has been removed. This results in the relettering of former Sec. 700-12(f) on unit equipment as (e).
Background: In some areas of the country the permission to tap ahead of the main was routinely granted in smaller occupancies for which a full emergency system source would be a tremendous burden. In most areas, however, this permission was simply never granted as a matter of policy. The reason is that it only provides something the normal system in the building does not provide in the event the service disconnect has opened.
Very few outages result from service disconnects opening. Most originate in utility failures, for which the connection ahead of the main is useless. Furthermore, this source is not recognized in other standards as an appropriate source, and it has been deleted.
Correllation note: Sec. 700-1 (FPN No. 3) identifies fire pump circuits as part of the emergency system, or at least eligible for inclusion in that system. Sec. 695-3(b) expressly recognizes a tap ahead of a service disconnect as a permitted source for a fire pump system. This has created a direct conflict with the deletion of the permission to tap ahead of the main in this article. Check with the AHJ to see how this will be applied to fire pumps.
EC&M recommendation: Allow the tap for the fire pump. Remember, the fire pump provisions are based on concerns about firefighters deciding to disconnect the building and ending up opening every service switch including the fire pump disconnect. The prospect of a utility outage is covered in different provisions in Art. 695.
Sec. 710-4(b)(1). The requirement for protecting medium voltage conductors emerging from grade now extends below the grade line.
What happened: The protection rules now apply "from the minimum cover depth to a point..." instead of "from the ground line ..."
Background: This makes this section of the NEC consistent with similar material in Sec. 300-5(d) for conductors on systems 600V and below. Protecting conductors only to the ground line isn't enough; over time if the earth settles or erodes, the result will be exposed conductors. On these higher voltage systems it made no sense to have a more lenient rule than the one that covers conductors 600V and below.
EC&M tip: Don't forget that although Art. 710 amends various rules in Art. 300, new Sec. 300-5(j) isn't one of them. You must allow for possible future ground movement at the point of cable entry to the riser. This can be as simple as leaving a little slack ("S" loop) at the transition.
Sec. 710-4(b)(2). A new exception allows shielding to be interrupted at a medium voltage buried cable splice.
What happened: The metallic shielding on directly buried single-conductor medium voltage cables that have maintained spacing between phases and that are part of an "engineered cabling system" is now permitted to be discontinuous at a splice. The shielding must be arranged to overlap ("interrupted and overlapped"). Each shield segment created through this process must be grounded at one point.
Background: Medium voltage conductors that run significant distances as single conductor cables with maintained spacing in the ground often develop very significant circulating currents in the shielding when the shielding is grounded at both ends. These currents add to the overall heating in the cable, reducing its ampacity. One solution is to break the cable at mid-run, and leave the shield discontinuous at that point. This new exception permits this arrangement, provided the shields overlap at this joint. Each shield segment must be grounded, but at a single point. This exception applies only to an engineered cabling system.
Sec. 720-11. A new section reiterates the requirement in Sec. 110-12 for work to be done in a neat and workmanlike manner. In addition, cables must be supported by the building structure "in such a manner that the cable will not be damaged by normal building use."
This will prevent such practices as running limited energy cables over a hot transformer or where they would be subject to physical damage and eventually fail. The same rule went into Art. 725, 760, and 770. Note that this article, although restricted to 50V, isn't really a limited energy article. Although the voltage is limited, the amount of current is not, and therefore there are no amendments to the rules of Chapter 3. A new FPN lists a telecommunications wiring standard as providing a way to determine accepted industry practice in this area.
Sec. 725-41. This is a new section on Class 2 and Class 3 power supplies. It restricts the allowable power sources for these circuits to those officially listed or inherently power limited, according to a five-item list.
What happened: Class 2 (and 3) power supplies must now consist of one of five items, none of which can be constructed in the field without benefit of listing:
* A listed Class 2 or Class 3 transformer.
* A listed Class 2 or Class 3 power supply.
* Other listed equipment marked to identify the Class 2 or Class 3 power source. A FPN gives examples of circuit cards so listed and part of a listed assembly, a current-limiting impedance (either listed or part of a listed product) used with a nonpower-limited stored energy source such as a storage battery, or a thermocouple. An exception waives the requirement for thermocouples to be listed as a Class 2 power source.
* Listed information technology (computer) equipment limited power circuits. A FPN cites UL 1950 as the applicable product standard and notes that such circuits are used "to interconnect information technology equipment for the purpose of exchanging information (data)." Although these circuits operate well within Class 2 parameters, the industry didn't want them marked that way because that term has a different meaning in Europe and they didn't want to use different markings depending on whether the products were being exported.
* A dry cell battery is still considered an inherently limited Class 2 power source, provided the voltage isn't over 30V and the capacity doesn't exceed series connected No. 6 carbon zinc cells. This used to be Note 4 to the power limitation tables.
Former Sec. 725-32 forbidding interconnection of class 2 sources unless so listed has been relocated here, to follow the list as subsection (b). FPNs following the opening language in sub-section (a) complete the picture. The first note refers to a new drawing showing the relative locations in the circuit, and in Art. 725, of the essential elements of Class 2 and 3 circuits. The second note refers to Tables 11a and 11b in Chapter 9 as the location for the listing requirements for Class 2 and Class 3 sources. These tables are the former Tables 725-31(a) and (b) which have been relocated into Chapter 9.
Background: The purpose of relocating these tables was to make it as clear as possible that they should be used by manufacturers and testing laboratories as part of the listing process, but they were not to be used in the field. There has been ongoing controversy as to whether the Code allowed, and whether it should allow, construction of Class 2 (or 3) power supplies in the field without benefit of listing. That question has been answered.
This is not, however, as big a change as it appears. A field-constructed Class 2 power supply that supposedly met all the rules usually wasn't actually verified as such. The reason was that even if it nominally met the current and voltage limitations in the tables, the maximum current and apparent power ([I.sub.max] and [VA.sub.max]) as defined in the Table notes virtually required testing lab facilities to verify. Remember, it had to have been measured with overcurrent protection bypassed if used. Merely inspecting the size of the overcurrent device and comparing it with the table didn't do it, and hasn't done it since the tables first appeared in the 1975 NEC. This code change should end the misapplications.
Sec. 725-54(a)(1) Ex. 2. This exception now has an important new option to cope with the requirements for system separation between power-limited and nonpower-limited circuits where these systems terminate in the same enclosure.
What happened, and why: The main rule requires nonpower-limited wiring to be fully divorced from power-limited circuits, such as Class 2 circuits under this article, regardless of the voltage rating of the individual conductors. These circuits do not rely on insulation rating alone to ensure safety; being insulated for the maximum circuit voltage per Sec. 300-3(c)(1) has never been sufficient separation for these systems.
If, however, a Class 2 circuit conductor operates the coil of a relay that switches a power circuit (or a nonpower-limited control circuit), then obviously both systems need to be in the same enclosure. If this happens, the previous rule required a 1/4-in. separation to be maintained between those conductors. The drawing shows how that separation could be obtained in a small energy management octal-based relay enclosure.
As the drawing indicates, observing this rule can be very difficult. There are other applications where that separation cannot be reliably observed at all, such as where the device with both nonpower-limited and power-limited connections is pushed blindly into a device box. This problem has precluded UL from listing some dimmer arrangements with a Class 2 remote control connection on the dimmer.
Now there is another option. If the power-limited circuits use Class 3 cabling (which has a higher voltage rating), and if the nonpower-limited circuits run 150V or less to ground, then the limited-energy cable can enter the same enclosure as an intact cable assembly without observing the 1/4-in. separation rule. Then, the individual conductors extending beyond the cable jacket must (if not adequately separated) be separated with a nonconductive barrier, or with a "nonconductive sleeve" from all other conductors. Although complicated, this should prove to be a workable solution to a very common design problem.
The other way out is to set the Class 2 or Class 3 circuit up as though it were a Class 1 circuit, and that also is now recognized in this exception. Note, however, that once as a Class 1 circuit, always as a Class 1 circuit. That means that the control devices on that circuit must qualify as Class 1 devices. Some manufacturers of remote-control gasoline dispensers have done this in order to allow their control circuit conductors to run in power raceways. Although their equipment uses data-processing circuits that are extremely limited in energy, they have obtained Class 1 ratings accordingly.
Sec. 725-54(a)(1) Ex. 3. A new exception allows power-limited and non-power limited conductors in a common raceway opening to enter an enclosure to connect to the same equipment. If the enclosure has only a single opening, the two systems can enter through a single tilting (such as a tee). The power-limited circuit conductors must be separated from the other conductors by a "continuous and firmly fixed nonconductor, such as flexible tubing."
This new exception, in concert with the extensive revisions to Ex. 2, should solve any remaining field problems with installing different systems on the same equipment. The idea behind this exception is that not much can go wrong over such a short distance, and the entire length of supplementary nonconductive tubing can be inspected. Note that this exception is not limited to 150V-to-ground applications.
Art. 727. There is a new article covering a control circuit wiring method, Instrumentation Tray Cable.
What it is and why it is: It is defined as "a factory assembly of two or more insulated conductors, with or without grounding conductors, and enclosed in a nonmetallic sheath or armor." This article has only one reason for existence, and that is to get around Sec. 725-27(b) which requires 600V insulation on Class 1 control circuits.
There are countless industrial control systems where (1) the actual circuits cannot possibly meet Class 2 standards, (2) conductors with 600V insulation cannot possibly terminate where they need to due to insulation thickness, such as on computer logic boards, and (3) 300V insulation is more than safe for the intended use. These realities have left the industrial users of these systems in an untenable position for years, and this new article points to a way out.
EC&M tip: The article made its way into the Code through a highly unorthodox procedure that has left it uncorrelated with Art. 725. The discussion that follows includes some suggestions for addressing those issues. Be sure to discuss them carefully with the AHJ.
Sec. 727-3. This wiring method is not permitted on circuits running over 150V to ground or drawing more than 5A, nor can it be used with power, lighting, and nonpower-limited circuits. There are two exceptions:
* "Where terminated within equipment or junction boxes and separations are maintained by other means."
This is very vague, but remember, these are 300V Class 1 conductors. A reasonable way to apply this exception is to classify the ITC cable conductors as a Class 3 cable construction for the purposes of this rule only. Then apply the separation rules in the revised Sec. 725-54(a)(1) Ex. 2 or Ex. 3 as applicable. That should be a reasonable approach that will allow the users to do what needs to be done safely.
* "Where a smooth metallic sheath, welded and corrugated metallic sheath, or interlocking tape armor is applied over the nonmetallic jacket." This is another way to make the separation between systems.
Sec. 727-4. This cable is available in sizes No. 22 to No. 12, either copper or thermocouple alloy. The insulation must be rated for 300V and shielding is permitted.
This is the nub of the entire question, and nothing in Sec. 725-27 recognizes 300V insulation on Class 1 control circuits. Note also, that one reason for the 600V requirement in Art. 725 is for additional protection when control circuits serve a life-safety function under Sec. 725-8(a). Therefore, there is still a conflict, and the AHJ will need to decide. There is an old principle of statutory interpretation, that when two provisions are in partial conflict you should try to read them in concert and not as mutually exclusive. One way to do that here is to allow the Type ITC cable as intended on all circuits for which it is otherwise intended and appropriate, but require 600V insulation on life-safety circuits. Usually those terminations will be suitable for 600V anyway.
Sec. 760-71 (a). The "special stranding" rules that formerly limited cables for fire alarm work to solid or bunch-tinned copper, with exceptions for certain strandings, have been deleted.
What happened: This section required solid or bunch-tinned copper for fire alarm circuits, with exceptions for up to 7-strand No. 16 and No. 18, and up to 19-strand for No. 14 and larger. These rules have been deleted. The only remaining requirement is that the conductors be "solid or stranded copper."
Background: The stranding restrictions originated when fire alarm systems were much less complicated, and less supervised than current systems. The fear was that if only a single strand remained in a circuit, the circuit would show intact to the supervisory relay. Nevertheless, if that circuit the went into alarm, with the relatively high-current alerting devices involved, the single strand might then burn clear and kill the alarm.
Modern fire alarm circuits are monitored and tested differently, and even if this problem did happen, it would be found during testing. There was not a single actual reported example of that having happened during the public comment period. There was concern about floating strands contacting adjacent terminals, but modern pressure terminal design (instead of backwrapped screw terminals) seems to be taking care of that.
Dropping the "special stranding" rules opens the door to a single limited-energy cable being allowed, and commonly used, on all limited energy systems. This will undoubtedly be the future direction of the cable industry.
Sec. 780-3. The words "of a closed-loop power distribution system" have been added after the word "Outlets" in Sec. 780-3(a), and "in a closed-loop power distribution system" at the beginning of Sec. 780-3(b)(1) in an attempt to create a distinction between closed-loop and programmed power.
Programmed power uses more conventional devices, and Sec. 780-7 on noninterchangeability would not apply according to this approach. This change would make "smart-house" type equipment capable of plugging into conventional receptacles and thereby more easily recognizable to the consumer, while allowing a later transition to true closed-loop power.
This interpretation is highly controversial. There is no consensus that the scope of this article ever intended such a distinction. The scope describes a "signaling between the energy controlling equipment and the utilization equipment." In conventional programmed power that signaling is between a controller and a programmable device. The utilization equipment is passive, turning on or off by the outlet becoming energized or deenergized, and does not communicate with the controller.
Art. 336 was just rewritten to accommodate a hybrid cable to be used for this wiring. Sec. 336-4(c) requires this cable to be used "as permitted in Art. 780." This cable is going into many houses on the assumption it will be usable as installed, even if for conventional outlets that don't meet the unique configuration rules in Sec. 780-7. Depending on how this change is applied, that may cause consternation at best. This is another one to discuss with the AHJ before you get over your head.
Chapter 9, Table 1. The notes to this table now include all notes, rearranged and revised to reflect customized wiring method dimensions for each of all the tubular wiring methods. This is a major change, undoing standard calculation practices going back generations. For conductors all of the same size, the resulting fill tables now add over 80 pages to the book as a new Appendix C.
What happened: Raceway fill is now being micromanaged, customized to each of the Chapter 3 wiring methods for which a fill calculation must be made. This means that the internal dimensions of each of these wiring methods must be individually tabulated, instead of working with a nominal diameter that applied per trade size across all wiring methods. The result, in a nutshell, is Tables 2, 3A, 3B, and 3C no longer exist, Table 4 now has individualized dimensions for each wiring method, and Tables 5 and 5A still have dimensions for conductors. These last tables, however, have been completely revised and the dimensions of many conductors significantly changed to reflect current production practice.
Background: In response to numerous proposals to correct errors in the tables in the previous code cycle, NEMA set up a task group to correct the tables. Each raceway, with the exception of liquidtight flexible nonmetallic conduit [Type B, corresponds to Sec. 351-22(2)] and liquidtight flexible metal conduit have different internal diameters. Here are the actual 40% cross-sectional areas of 2-in. raceways:
* 1.342 [in.sup.2]: EMT
* 1.282 [in.sup.2]: ENT
* 1.452 [in.sup.2]: IMC
* 1.363 [in.sup.2]: RMC
* 1.307 [in.sup.2]: FMC (flex)
* 1.298 [in.sup.2]: LTFNMC-B
* 1.298 [in.sup.2]: LTFMC
* 1.316 [in.sup.2]: RNMC-Sch. 40
* 1.150 [in.sup.2]: RNMC-Sch. 80
* 1.340 [in.sup.2]: Old Table 4
As this shows, the old Table 4 tended to understate the area for steel raceways, and overstate it for nonmetallic and flexible raceways. This combined with errors in the conductor size tables to make it problematic to properly determine raceway fill. For example, 1/2-in. EMT (or any other raceway of the same trade size) used to be able to hold 10 No. 12 THHN conductors. The tabulated cross-sectional area for No. 12 THHN has gone from 0.0117 [in.sup.2] to 0.0133 [in.sup.2], which, in turn, reduces the allowable wire fill in 1/2-in. EMT from 10 to 9 conductors. Given the differences in raceway diameters, however, 1/2-in. rigid nonmetallic conduit drops to 8 No. 12 THHN, whereas the larger 1/2-in. intermediate metal conduit stays at 10 No. 12 THHN. These discrepancies apply to virtually every wire fill calculation, and may have a significant effect on your work.
Table B-310-11, FPN. The FPN to this table has been reworked to better explain the origin of the ampacity limits in Note 8(a), although the wording is still very unclear.
This table, for generations, was the derating table for multiple conductors in a raceway, in the old Note 8. It turned out that the original Note 8 table assumed half the conductors were control circuit conductors and not carrying current. This meant, in turn, that the old rules were anticipating a load diversity of at least 50%.
Using the [I.sup.2]R relationship the derating factors in Table B-310-11 can be adjusted for diversity less than 50%. The revised FPN does exactly that, although not too clearly. Here, in a nutshell, is how to apply the revised note:
* Think of the formula in three parts: the ampacity you want, the ampacity you would have figured before the 1987 NEC discovered a diversity problem, and a factor to connect the two.
* The ampacity you would have figured in the past before 1987 is simply the appropriate table factor multiplied by the Table 310-16 (or other table) ampacity.
* The factor is simply the square root of the ratio of one-half the number of conductors being considered potentially current-carrying to the number of those conductors that are reasonably defined as current carrying at any one time.
* The ampacity you want is the old ampacity (prior to 1987) times the factor.
* Example: What will be the ampacity of No. 12 THHN conductors in a raceway with 24 such conductors in it, 20 energized at one time? All could be current carrying.
* Answer: 1) Old ampacity derating factor, 24 conductors, is 70%; 0.7 x 30A = 21A. 2) Factor, [square root of (0.5 x 24/20) = 0.77]. 3) Result: 21A x 0.77 = 16A. This compares with 45% allowed under Note 8(a): 30A x 0.45 = 13.5A.
This can provide reasonable calculations for many applications. The drawing shows that multiple conductor installations are safe as long as the [I.sup.2]R heating doesn't exceed the old Note 8 loading at 50% diversity. Remember, the access to this table is through Sec. 310-15(b), which is by engineering supervision only. The results of this small change may be far-reaching in occupancies with the appropriate support.