3.2 How a temporary power installation is supposed to be built
Temporary power is the electrical system nobody owns. It goes in fast, it feeds every trade, it gets moved by whoever needs the outlet, and it is gone before the building is finished. OSHA wrote a whole paragraph for it — 29 CFR 1926.405(a)(2) — precisely because it may be built to a class less than a permanent installation. This chapter is what that paragraph actually requires, in the order you meet it walking from the panel to the tool.
1 What "temporary" does and does not excuse
1926.405(a)(2)(i) sets the terms: the provisions apply to temporary electrical power and lighting wiring methods "which may be of a class less than would be required for a permanent installation." Then the sentence that matters: "Except as specifically modified in paragraph (a)(2) of this section, all other requirements of this subpart for permanent wiring shall apply to temporary wiring installations."
In other words, temporary buys you a lighter wiring method and nothing else. Grounding, guarding, overcurrent protection, ground-fault protection and the cord rules all still apply. And the same paragraph adds an ending most sites forget: temporary wiring "shall be removed immediately upon completion of construction or the purpose for which the wiring was installed."
2 From the source to the outlet
| Element | Requirement | Paragraph |
|---|---|---|
| Feeders | Originate in a distribution center; run as multiconductor cord or cable assemblies or in raceways, or — where not subject to physical damage — as open conductors on insulators not more than 10 feet apart | (a)(2)(ii)(A) |
| Branch circuits | Originate in a power outlet or panelboard; all conductors protected by overcurrent devices at their ampacity; open runs located where they will not be damaged and fastened at intervals not exceeding 10 feet; no branch-circuit conductors laid on the floor; a separate equipment grounding conductor where run as open conductors | (a)(2)(ii)(B) |
| Receptacles | Grounding type; unless in a complete metallic raceway, each branch circuit contains a separate equipment grounding conductor and all receptacles are connected to it; receptacles for uses other than temporary lighting may not be on lighting branch circuits | (a)(2)(ii)(C) |
| Disconnects | Disconnecting switches or plug connectors installed to permit disconnection of all ungrounded conductors of each temporary circuit | (a)(2)(ii)(D) |
| Lamps | All lamps for general illumination protected from accidental contact or breakage; metal-case sockets grounded | (a)(2)(ii)(E) |
| Suspension | Temporary lights may not be suspended by their electric cords unless the cords and lights are designed for it | (a)(2)(ii)(F) |
| Wet and conductive locations | Portable lighting used in wet or other conductive locations — drums, tanks, vessels — operated at 12 volts or less; 120-volt lights only if GFCI protected | (a)(2)(ii)(G) |
| Flexible cords | Protected from damage; sharp corners and projections avoided; cords may pass through doorways or other pinch points only if protection is provided | (a)(2)(ii)(I) |
| Extension cord sets | Three-wire type, designed for hard or extra-hard usage; cords for temporary and portable lights likewise hard or extra-hard usage | (a)(2)(ii)(J) |
3 The three lines crews break most
Conductors on the floor. (a)(2)(ii)(B) is one short sentence — "No branch-circuit conductors shall be laid on the floor" — and it is broken on nearly every site, because a run of cord across a slab is the fastest way to get power to a corner. On the floor a conductor gets driven over, walked on, buried under material and soaked. The rule exists because damage on the floor is not a possibility, it is a schedule.
Lights hanging by their cords. (a)(2)(ii)(F). A string light hung from its own conductor is a strain-relief failure waiting to happen, and the failure shows up as exposed conductor at head height.
Receptacles on the lighting circuit. (a)(2)(ii)(C) prohibits receptacles for other uses on branch circuits supplying temporary lighting, and prohibits connecting them to the same ungrounded conductor of multiwire circuits that supply lighting. The practical reason is immediate: when a tool trips that circuit, the floor goes dark with people on it.
4 Lighting, guards and what a broken lamp costs
Temporary lighting is the part of the installation that everyone touches. (a)(2)(ii)(E) requires all lamps for general illumination to be protected from accidental contact or breakage, and metal-case sockets to be grounded. 1926.405(j)(1)(iii) adds four rules for portable handlamps: no metal shell, paper-lined lampholders (A); a handle of molded composition or other insulating material (B); a substantial guard attached to the lampholder or handle (C); and any metallic guard grounded by an equipment grounding conductor run within the power supply cord (D). Under (j)(1)(iv), lampholders installed in wet or damp locations must be of the weatherproof type, and (j)(1)(i) requires fixtures, lampholders, lamps and receptacles to have no live parts normally exposed to employee contact.
5 A five-minute walk-down anyone can do
- 1Find the distribution point. Is there a real panel or power outlet, with a disconnecting means for every temporary circuit — or a strip of receptacles fed from something nobody can identify?
- 2Follow one circuit. Is any part of it lying on the floor, run through a doorway unprotected, or fastened with a staple?
- 3Look at the receptacles. Grounding type? GFCI or covered by the assured grounding program? Standing in water?
- 4Look up at the lights. Guarded lamps? Hanging by the cord? Metal sockets grounded?
- 5Look in front of the panel. 30 inches clear, door opens 90 degrees, nothing stored, lit.
6 One more line worth knowing: guarding at 50 volts
Temporary does not lower the guarding threshold. 1926.403(i)(2)(i) requires live parts of electric equipment operating at 50 volts or more to be guarded against accidental contact — by cabinets or enclosures, by location in a room or vault accessible only to qualified persons, by partitions or screens, by location on an elevated balcony or platform, or by elevation of 8 feet or more above the floor. Where equipment would be exposed to physical damage, (i)(2)(ii) requires enclosures or guards arranged and strong enough to prevent it.
An open temporary panel with the deadfront missing, sitting at chest height in a traffic lane, fails all five of those options at once. It is also the exact configuration crews stop noticing after week two.
7 Who owns the temporary system
The recurring failure of temporary power is not technical. It is that the installation belongs to everyone and to no one: the electrical sub installs it, every trade uses it, and after the first month nobody is sure who is allowed to change it. Three questions settle it, and they belong in the pre-construction meeting rather than in an inspection finding.
Who installs and modifies it? Adding a spider box, moving a panel or extending a feeder is electrical work on a construction site, and Subpart K applies to it as it applies to permanent wiring. A trade that needs power in a new location asks; it does not extend the system itself.
Who inspects it, and how often? If the site runs an assured equipment grounding conductor program, 1926.404(b)(1)(iii)(B) already names the answer: one or more competent persons designated to implement it, with the daily visual inspection of (C) and the quarterly tests of (E). If the site runs GFCIs instead, the equivalent discipline is testing the devices and replacing the ones that fail.
Who takes it out? 1926.405(a)(2)(i) requires temporary wiring to be removed immediately upon completion of construction or of the purpose for which it was installed. Abandoned temporary circuits left energized in a finished building are one of the more dangerous artifacts a project can leave behind, because the next person to find them has no drawing and no reason to expect them.
- "Temporary" buys a lighter wiring method only; every other requirement of Subpart K still applies, and the wiring comes out when the work is done (1926.405(a)(2)(i)).
- Feeders start at a distribution center, branch circuits at a power outlet or panelboard, and no branch-circuit conductor is ever laid on the floor.
- Receptacles are grounding type and are not mixed onto temporary lighting circuits.
- Lamps for general illumination are guarded against contact and breakage; lights are not suspended by their own cords.
- Portable lighting in drums, tanks and vessels runs at 12 volts or less, or 120 volts with a GFCI; handles and screw-shell lampholders in wet locations are non-conducting.
- Extension cord sets used with portable tools are three-wire and designed for hard or extra-hard usage — 1926.405(a)(2)(ii)(J).
Free educational content — not OSHA-authorized training, no certificate or card issued. Follow your employer's program and the standards cited.