Most of the Art. 520 requirements are in one of four Parts (II, III, IV, and V). Part I provides the general requirements. Part VI provides requirements specifically for dressing rooms, and Part VII is a paragraph we’ll discuss last.
The types of locations covered by Art. 520 (Photo) tend to make extensive use of portable equipment. You can use approved flexible cords and cables for portable switchboards and other portable equipment [520.5(B)]. This requirement is a fork in the road. Take one fork, and you’re dealing with requirements for portable switchboards. Take the other, and it’s portable equipment. Taking that first fork, we go to Part V.
Portable switchboards (on stage)
The NEC doesn’t construct the requirements for fixed versus portable switchboards in a way that permits side by side comparison. This makes sense because one is not a variation of the other.
The requirements for portable switchboards are in Part IV, Sections 520.50 through 520.53. The first set of requirements is for road show connection panels:
• Their construction must comply with Art. 408.
• Circuits must originate in grounding-type polarized inlets; voltage and current ratings must match those of the receptacles.
• Where circuits transfer between fixed and portable switchboards, all conductors must transfer simultaneously.
• Branch circuit overcurrent protective devices (OCPD) must protect each circuit installed in the panel and the supply devices of the panel.
Most of the other requirements are about what you’d expect. For example, the switchboards must contain overcurrent protection for branch circuits [520.52]. But in this case, as with some other requirements in Part IV, there’s a twist. The permissible load requirements for multiple outlet branch circuits, provided in 210.23, don’t apply.
Part IV specifically states that only qualified personnel can do certain things pertaining to these systems [520.53(P)]. Those things are basically the electrical work required to set up these systems. But Art. 520 doesn’t present this same requirement for other types of portable equipment or for fixed equipment. From this anomaly, it’s possible to draw the conclusion that unqualified personnel are authorized to connect fixed equipment. But that would be wrong, because Art. 90 and OSHA both contain the qualified personnel requirement and state it applies to all installations.
So why the one-off mention? If you read 520.53(P) closely, you’ll see it requires that the equipment be permanently and conspicuously marked with the requirement. The first thing it identifies is the routing of the conductors. Energizing and de-energizing are also on that list. This addresses a particular set of problems (e.g., people thinking it’s OK to “hit the switch”) with this particular equipment by making it very clear to unauthorized personnel that this equipment is off limits to them.
Fixed switchboards
The 2014 NEC changed these requirements. Sections 520.21 through 520.24 have been replaced by all new text in 520.21. A fixed switchboard must:
• Be listed.
• Be readily accessible.
• Contain OCPDs.
Additionally, it can supply both stage and non-stage equipment.
The dimmer requirements are the same as for the 2011 NEC [520.25]. All of these are important, but make sure any resistance-type dimmers comply with 404.24(B).
You can supply these switchboards by:
• A single feeder [520.27(A)(1)]. Ensure it disconnects with a single disconnect.
• Multiple feeders to an intermediary patch panel [520.27(A)(2)]. Among other things, ensure the neutral conductors in each raceway have sufficient ampacity to carry the maximum unbalanced current supplied by the feeder conductors in that raceway.
• Separate feeders to single primary stage switchboard [520.27(A)(3)]. A key requirement is the switchboard has a permanent and obvious label stating the number and location of disconnects.
Portable equipment other than switchboards
Portable power distribution units (PPDUs) differ from switchboards. A PPDU is a box containing receptacles and OCPDs [520.2]. A couple of important requirements [520.62]:
• Bus bar ampacity must equal the sum of the ampere ratings of all circuits connected to it.
• Cables must be arranged so that tension on the cables isn’t transmitted to the terminations.
Arc lamps must be listed [520.61]. Cord sets and cables must be listed, and cables must be extra-hard usage type [520.61]; this applies to all flexible conductors [520.68(A)(1)].
Luminaire supply cords can’t be longer than 3.3 ft and must be protected by an OCPD no larger than 20A [520.68(A)(3)].
If you’re going to use adapters, two-fers, or other outlet devices, the receptacle, cable, and supply plug must have the same current and voltage rating [520.69].
Fixed equipment other than switchboards
This equipment consists of such things as for footlights, border lights, and proscenium lights. For these types of lights, the branch circuits can’t exceed 20A [520.41]. Circuits consisting of only heavy-duty lampholders can exceed 20A if conforming to the relevant Art. 210 requirements.
Footlights have additional requirements covered by 520.43. Footlights of metal trough construction must, for example, meet dimensional requirements. Footlights of any other construction must consist of individual outlets. If you install disappearing footlights, make sure their current supply disappears when they do.
If you have any other fixed equipment, scan through the headings of 520.44 though 520.49 to see if any of these subsections provide requirements for that equipment.
No plastic raceways
The list of permissible raceways doesn’t include PVC raceways. You can use [520.5(A)]:
• Metal raceways.
• Nonmetallic raceways encased in at least 2 in. of concrete.
• Type MI cable.
• Type MC cable.
• AC cable containing an EGC sized per Table 250.122.
Why are the plastic Chapter 3 wiring methods not on this list? Because when they are burned or superheated, they give off highly toxic fumes. Consider your typical production stage with the high density of people and intense activity. Getting a quick and orderly evacuation is difficult, and the fumes might be faster than the people. So the materials just aren’t permitted.
The exceptions to this rule are:
• Audio signal processing and similar equipment; apply Art. 640.
• Communications circuits; apply Art. 725 as appropriate.
• Fire alarm circuits; apply Art. 760.
But if the applicable building code doesn’t require fire-rated construction, you can use nonmetallic sheathed cable, Type AC cable (no EGC required), electrical nonmetallic tubing, or rigid metallic conduit [520.5(C)].
Dressing rooms
Exposed incandescent lamps are traditional and ubiquitous. A lamp guard requirement applies to any of these that are less than 8 ft from the floor [520.27], which means the lamp guard requirement nearly always applies.
A wall switch requirement also applies to these lights and to any receptacles. The NEC provides a detailed requirement that, with some imagination, you could circumvent if you really wanted to. But the idea is that the curling irons, hair dryers, and other appliances used in front of that dressing room mirror will all be shut off when the occupant leaves the room. Pursuant to this idea, a pilot light outside the room is also required [520.73].
You cannot install pendant lampholders in dressing rooms [520.71].
Part VII
This two-sentence paragraph reveals some language reconciliation that still remains to be done in the NEC. Wherever the NEC refers to “equipment grounding conductors,” it means a bonding system (see Art. 100 definitions of grounding and bonding). This puts metal enclosures at the same electrical potential, preventing touch potential hazards and flashover hazards.
Saving 520 time
Running about nine pages, Art. 520 could take up considerable time for the under-pressure electrician who is making those unplanned changes that are inevitable in these types of venues. How can you ensure your work meets Code without wading through the whole Article every time there’s a change?
First, note that Art. 520 consists of seven Parts. Two of them (Parts II and III) address fixed equipment and two (Parts IV and V) address portable equipment. Part VII (the last one) is a paragraph that basically says to bond all metallic objects.
So right away, you see you don’t have to refer to Part VII. Just ensure you always bond equipment to the equipment grounding (bonding) conductor.
Next, determine if the equipment is fixed or portable.
• If it’s fixed and not a switchboard, apply Part III. If it’s a fixed switchboard, apply Part II.
• If it’s portable, use the same nonswitchboard/switchboard logic. Apply Part V or IV, respectively.
If the work involves a dressing room, apply Part VI. The key there is to ensure everything can be switched off when the occupant leaves the room, and there’s a pilot light by the door to confirm it.
Everything falls under Part I, except this also has some division of requirements for fixed vs. portable. You have now narrowed down how much of Art. 520 you need to apply to the given job at hand.
Lamendola is an electrical consultant located in Merriam, Kan. He can be reached at [email protected].
