Stumped by the Code? February 2011

Stumped by the Code? February 2011

Your most pressing National Electrical Code (NEC) questions answered

All questions and answers are based on the 2008 NEC.

Q. Does the NEC require GFCI or tamperproof receptacles for replacement purposes in existing dwelling units?

A. When receptacles are replaced in locations where GFCI protection is required, the replacement receptacles must be GFCI-protected. This includes the replacement of receptacles in dwelling unit bathrooms, garages, outdoors, crawl spaces, unfinished basements, kitchen countertops, rooftops, or within 6 ft of laundry, utility, and wet bar sinks. See 210.8 for specific GFCI-protection requirements [406.3(D)(2)]. Tamperproof receptacles are not currently included in this replacement receptacle requirement.

Q. What are the Code requirements for motor disconnects?

A. Each motor must be provided with a separate disconnecting means unless the controller disconnecting means meets the necessary requirements to serve the disconnect for both.

Section 430.102(B)(1) requires a disconnecting means for each motor, and it must be located in sight from the motor location and the driven machinery location. “Within Sight” is visible and not more than 50 ft from each other [Art. 100]. Or, the controller disconnecting means [430.102(A)] can serve as the disconnecting means for the motor if the disconnect is located in sight from the motor location [430.102(B)(2)], as shown in the Figure.

A motor disconnecting means isn’t required under either of the following conditions if the controller disconnecting means [430.102(A)] is capable of being locked in the open position. The provision for locking or adding a lock to the disconnecting means must be installed on or at the switch or circuit breaker and remain in place with or without the lock installed [430.102(B)(1) and (2), Ex].

  • Where locating the disconnecting means is impracticable or introduces additional or increased hazards to persons or property.
  • In industrial installations, with written safety procedures, where conditions of maintenance and supervision ensure only qualified persons will service the equipment. This should include lockout/tagout procedures.

Some additional requirements for motor disconnects include:

  • The disconnecting means for the motor controller and the motor must open all ungrounded supply conductors simultaneously, and it must be designed so that it will not close automatically [430.103].
  • The controller and motor disconnecting means must indicate whether they are in the “on” or “off” position [430.104].
  • The disconnecting means must be legibly marked to identify its intended purpose [110.22 and 408.4], and when operated vertically, the “up” position must be the “on” position [240.81 and 404.6(C)].
  • Either the controller disconnecting means or motor disconnecting means required by 430.102 must be readily accessible [430.107].

The disconnecting means for the motor controller and/or the motor must be a [430.109(A)]:

  • A listed horsepower-rated motor-circuit switch.
  • A listed molded-case circuit breaker.
  • A listed molded-case switch.
  • Listed manual motor controllers marked “Suitable as Motor Disconnect.”

For stationary motors of two horsepower or less, the disconnecting means is allowed to be a general-use AC snap switch, where the motor full-load current rating isn’t more than 80% of the ampere rating of the switch [430.109(C)].

A horsepower-rated attachment plug and receptacle having a rating not less than the motor rating is allowed as the disconnecting means for cord- and plug-connected motors [430.109(F)].

A horsepower-rated switch or circuit breaker can serve as both a controller and disconnecting means if it opens all ungrounded conductors to the motor, as required by 430.103 [430.111].

Q. What are the NEC requirements regarding an equipment grounding conductor installed with a feeder to a panelboard?

A. Section 408.40 requires that metal panelboard cabinets and frames must be connected to an equipment grounding conductor of a type recognized in 250.118 [215.6 and 250.4(A)(3)]. Where the panelboard is used with nonmetallic raceways or cables — or where separate equipment grounding conductors are provided — a terminal bar for the circuit equipment grounding conductors must be bonded to the metal cabinet.

There is an exception for insulated equipment grounding conductors for receptacles having insulated grounding terminals (isolated ground receptacles) [250.146(D)], which allows them to pass through the panelboard without terminating onto the equipment grounding terminal of the panelboard cabinet.

Equipment grounding conductors must not terminate on the neutral terminal bar, and neutral conductors must not terminate on the equipment grounding terminal bar, except as permitted by 250.142 for services and separately derived systems (see the definition of “Separately Derived System” in Art. 100).

Caution: Most panelboards are rated as suitable for use as service equipment, which means they are supplied with a main bonding jumper [250.28]. This screw or strap must not be installed except when the panelboard is used for service equipment or on separately derived systems [250.24(A)(5)]. In
addition, a panelboard marked “suitable only for use as service equipment” means the neutral bar or terminal of the panelboard has been bonded to the case at the factory, and this panelboard is restricted to being used for service equipment or on separately derived systems according to 250.142(B).

Section 215.6 also requires that feeder circuits must include or provide an equipment grounding conductor of a type listed in 250.118, and it must terminate in a manner so that branch circuit equipment grounding conductors can be connected to it, installed in accordance with 250.134.

Q. When can I “round up to the next size overcurrent device” when the conductor ampacity does not match a standard size overcurrent device?

A. The next higher standard rating overcurrent device (above the ampacity of the ungrounded conductors being protected) is permitted, provided all of the following conditions are met [240.4(B)]:

  1. The conductors do not supply multioutlet receptacle branch circuits.
  2. The ampacity of a conductor, after ampacity adjustment and/or correction, doesn’t correspond with the standard rating of a fuse or circuit breaker in 240.6(A).
  3. The overcurrent device overcurrent device rating doesn’t exceed 800A.

Example: A 400A overcurrent device can protect 500kcmil conductors, where each conductor has an ampacity of 380A at 75°C, in accordance with Table 310.16. This rule (i.e., “next size up”) doesn’t apply to feeder tap conductors [240.21(B)], or secondary transformer conductors [240.21(C)].

If the circuit’s overcurrent device exceeds 800A, then the conductor ampacity, after ampacity adjustment and/or correction, must have a rating not less than the rating of the overcurrent device [240.4(C)].

Example: A 1,200A overcurrent device can protect three sets of 600kcmil conductors per phase, where each conductor has an ampacity of 420A at 75°C, in accordance with Table 310.16.

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