2023 NEC Articles 500 to 518 and 590
Chapter 5 of the NEC adds rules for places where fire, explosion, or patient safety is a special concern, and Article 590 adds rules for wiring that is not permanent. Most GCHS work is ordinary, but rehab and construction management put you in three of these places often: a church hall or community building that counts as assembly, a clinic with patient care spaces, and every job site during construction. Hazardous locations and health care are taught here at a pointer level, so you can recognize when they apply and know that a specialist reads the rest. Assembly and temporary installations are taught in more detail, including the GFCI rules for construction. Local adoption governs which edition applies (see Lesson 1).
Article 500 sorts hazardous places by what is in the air and how often. Class I is flammable gas or vapor. Class II is combustible dust. Class III is combustible fibers and flyings (500.5(B), (C), (D)). Within a class, Division 1 means the hazard can be present under normal operation, or because of frequent repair, leaks, or a breakdown that could also make the equipment a source of ignition. Division 2 means the material is normally confined in closed containers or systems and escapes only through accidental rupture, failure, or abnormal operation (500.5(B)(1) and (B)(2)). The classification, its extent, and the equipment permitted inside are set by the designer and the authority having jurisdiction, and the detailed wiring rules of the articles that follow Article 500 then apply. Your job is to spot the trigger: a fuel dispenser, a paint booth, a grain or flour room, or a repair garage.
Parking garages used only for parking or storage are permitted to be unclassified (511.3(A)). Repair garages are different: a garage that dispenses fuel follows 511.3(B), and one that repairs vehicles using Class I liquids or heavier-than-air gaseous fuels such as LPG follows Table 511.3(C). GFCI protection in commercial garages is required as 210.8(B) says (511.12). A gasoline station follows Article 514. Its classified areas around dispensers come from Table 514.3(B)(1), unless the authority having jurisdiction determines that low-flash liquids such as gasoline will not be handled, in which case the location need not be classified (514.3(A)). Fuel dispensing systems must have one or more emergency shutoffs or electrical disconnects located not less than 20 ft nor more than 100 ft from the dispensers they serve (514.11(A)).
Article 517 covers clinics, medical offices, and hospitals, and the technical rules depend on the category of the patient care space. Two points are worth knowing. Branch circuits to patient care spaces need an effective ground-fault path: a metal raceway or a metal-armored or sheathed cable that itself qualifies as an equipment grounding conductor, plus an insulated copper equipment grounding conductor identified by green insulation (517.13(A) and (B)). Type NM cable does not meet that. And in a Category 2 space, each patient bed location needs at least two branch circuits, one from the critical branch and one from the normal system, and a minimum of eight receptacles (517.18(A) and (B)(1)). The two-circuit rule does not apply to patient bed locations in clinics and medical or dental offices, so it is mainly a hospital rule. Anything more detailed is for the designer and the health care authority.
Article 518 covers buildings, or portions of buildings, designed or intended for the gathering of 100 or more persons for worship, entertainment, eating, drinking, amusement, awaiting transportation, or similar purposes (518.1). The examples include assembly halls, auditoriums, gymnasiums, restaurants, conference rooms, multipurpose rooms, museums, and places of religious worship (518.2(A)). In a mixed building, Article 518 applies only to the assembly portion, and a room used for assembly by fewer than 100 persons and incidental to another occupancy is classified as part of that other occupancy (518.2(B)). That is why a church fellowship hall for 120 falls under it, while a conference room for 40 in an office does not.
The wiring method must qualify as an equipment grounding conductor or carry one, and the permitted methods are metal raceways, flexible metal raceways, nonmetallic raceways encased in at least 2 in. of concrete, and Type MI, MC, or AC cable (518.4(A)). NM cable, ENT, and rigid nonmetallic conduit are additionally permitted in buildings, or portions, that the building code does not require to be fire-rated construction (518.4(C)). Working spaces around outdoor equipment serving an assembly occupancy must be illuminated, and the lighting cannot be controlled by automatic means only (518.6).
Temporary wiring is a real installation with its own article, and the permanent-wiring rules still apply unless Article 590 modifies them (590.2(A)). Temporary wiring methods must also be approved for the conditions of use (590.2(B)). Time limits depend on the purpose. Temporary power and lighting is permitted during construction, remodeling, maintenance, repair, or demolition. It is permitted for not more than 90 days for holiday decorative lighting and similar purposes (590.3(B)), and that decorative lighting must be listed and labeled (590.5). It is also permitted for emergencies and tests (590.3(C)). Temporary wiring must be removed immediately when the construction or the purpose ends (590.3(D)).
Temporary services follow Article 230, and feeders and branch circuits are protected under 240.4 and 240.5 (590.4(A) to (C)). For temporary feeders and branch circuits, NM, NMC, and SE cable are allowed with no height limit and no building-construction-type limit, and without concealment in walls, floors, or ceilings. All receptacles are the grounding type, with an equipment grounding conductor to every one, and receptacles on construction sites may not be on a branch circuit that supplies temporary lighting (590.4(D)(1)). Fifteen and 20 ampere receptacles in wet locations use the in-use covers of 406.9(B)(1). Each temporary circuit needs a disconnect for all ungrounded conductors (590.4(E)). General-illumination lamps must be protected from contact and breakage by a luminaire or a lampholder with a guard, and a metal guard must be grounded (590.4(F)). Splices go in enclosures with covers, with limited construction-site exceptions (590.4(G)). Cords are protected at doorways and pinch points (590.4(H)). Feeder and branch-circuit cables and cords may not lie on the floor or ground, and vegetation may not support overhead spans (590.4(J)). Extension cords are exempt from that support rule.
Section 590.6 requires ground-fault protection for personnel on temporary wiring used to power equipment during construction, remodeling, maintenance, repair, or demolition. It applies to utility power and to power from on-site generators. The pathway depends on the receptacle.
| Receptacle on the job | Protection required (590.6) |
|---|---|
| 125 V, single-phase, 15, 20, or 30 A, not part of permanent wiring, in use by personnel | GFCI for personnel (A)(1) |
| Same ratings, but installed or existing as permanent wiring and used for temporary power | GFCI for personnel (A)(2) |
| 125 V and 125/250 V, 15, 20, or 30 A outlets on a portable generator of 15 kW or less | Listed GFCI for personnel (A)(3) |
| Other receptacles, such as 250 V or 3-phase | GFCI, or a written assured equipment grounding conductor program (B) |
An assured equipment grounding conductor program must be written and continuously enforced at the site by one or more designated persons who make sure the equipment grounding conductors of cord sets, temporary receptacles, and cord-and-plug equipment are installed and maintained. Temporary wiring over 600 volts needs fencing or barriers (590.7), and reused overcurrent devices must be examined for proper installation and signs of impending failure (590.8(A)).
A GCHS project manager walks a new clinic build. The pedestal has 12 tool receptacles rated 125 V and 20 A. All 12 need GFCI protection for personnel, and they can share protection at the breaker or use receptacle-type GFCIs. Two 250 V, 50 A receptacles serve a hoist and a welder. Those two need GFCI, or the site must run a written assured equipment grounding conductor program. A 12 kW portable generator sits by the loading area, and every 125 V and 125/250 V outlet up to 30 A on it needs listed GFCI protection, because it is 15 kW or less. Eight bare lamps light the stair on a separate circuit: they need guards, and no receptacles may be added to that circuit. Four groups of equipment, four different rules. Extension cords lying in the doorway get flagged under 590.4(H).
In the field
A GCHS rehab of a church annex includes a fellowship hall built for about 120. That puts the hall under Article 518, so the plan reviewer asks for the wiring method and the construction type, since NM cable is allowed in unrated construction only. During construction, the site walk is short and repeatable. Is every tool outlet GFCI protected, including the permanent receptacles the crew is borrowing? Are the lamps guarded and on their own circuit? Is anything laid on the floor or crossing a door? Is the generator's cord set or built-in protection listed for GFCI? The list takes five minutes, and it is the cheapest way to prevent shock injuries at a site.
1. A church building has a fellowship hall designed for 120 people, in the same building as classrooms and offices. Does Article 518 apply to the hall, and why?
2. A GCHS community building has a 150-person assembly hall in unrated Type V-B construction. May the electrician run Type NM cable in the hall under Article 518?
3. A grain-handling building has combustible grain dust in the air under normal operation in quantities that can form an ignitible mixture. How is the location classified under 500.5?
4. A Group S-2 open parking garage is used only to park passenger cars, with no repair or fueling. How does 511.3(A) treat its electrical classification?
5. A Group B clinic exam room is a patient care space. The electrician wired its branch circuits with Type NM cable and no metal raceway. Does that meet 517.13(A)?
6. A community center strings holiday decorative lighting on its front canopy as a temporary installation. How long may it stay up under 590.3(B)?
7. On a Group B construction site, an electrician connects eight 20 A receptacles to the same branch circuit that supplies the temporary lights. What does 590.4(D)(1) say?
8. A crew hangs bare lamps for general illumination from cords in the stairwell of a building under construction. What does 590.4(F) require?
9. A temporary feeder cable is laid across the ground from the service pedestal to a panelboard in an addition that is being built. What is the finding under 590.4(J)?
10. A hand drill on a new Group B construction site plugs into a 125 V, 20 A receptacle on a temporary pedestal that is not part of the building's permanent wiring. What protection does 590.6(A)(1) require?
11. During the rehab of a community center, workers plug tools into existing 125 V, 20 A receptacles that are part of the building's permanent wiring. Are those receptacles required to have GFCI protection for personnel?
12. A 12 kW portable generator on a construction site has 125/250 V, 30 A outlets. What does 590.6(A)(3) require for those outlets?
13. A 250 V, 3-phase, 50 A receptacle serves a welder on a Group B construction site. What does 590.6(B) require?
14. A convenience store's gasoline dispensers have their emergency electrical disconnect mounted on a post 10 ft from the dispensers. What is the finding under 514.11(A)?