The Basics of Temporary Installations

A shock or arc blast from a temporary installation can be just as deadly as one from a permanent installation, and either type of installation is capable of igniting a fire if the conductors overheat or an arc is produced by faulty wiring. It is only reasonable that the same rules in regard to workmanship, conductor ampacity limits, and overcurrent protection should apply to both kinds of installations.

Temporary installations are not different because of relaxed care in respect to maintaining a safe installation, although Art. 590 does allow some modifications in certain wiring methods and materials. A temporary installation is different because it has an expiration date; in other words, there are time constraints on the use of temporary installations. In some cases, temporary installations must be removed after completion of the purpose for which it was installed, such as for construction or repair purposes [590.3(A)]. In others cases, there is a specific time limit for the use of a temporary installation. For example, a temporary installation for holiday displays can’t last more than 90 days [590.3(B)].

The removal aspect is evident in the Code requirements. For example, Type NM cable is allowed without height limitations in locations that would normally require raceway or metal sheathed cable type wiring methods for a permanent installation [590.4(C)], and a box is not required for most splices or junction connections where the circuit conductors are multiconductor cord or cable assemblies [590.4(G)].

Temporary installations provide some savings on installation costs and easier removal after completion of their purpose at what might be viewed as a slight relaxation of installation standards, when compared to more permanent wiring methods. However, limitations on the uses of temporary installations help to maintain a margin of safety.

Temporary wiring is only allowed for:

Construction, remodeling, maintenance, repair, or demolition of buildings, structures, or equipment — or similar activities [590.3(A)].
Emergencies, tests, experiments, and developmental work [590.3(C)].
Temporary wiring must be removed immediately upon completion of construction or the purpose for which it was installed [590.3(D)].

Who’s your AHJ?

The local inspector isn’t the only AHJ over your temporary installations — there can be multiple AHJs, such as:

OSHA has codified requirements in 29 CFR 1926 Subpart K; they are nearly verbatim replication of the NEC requirements.
For construction: the general contractor, site owner, and occupant.
For facilities: the insurer, corporate safety manager, and VP of operations.
The local fire marshal, city engineer, or other permit-granting authority.

Temporary wiring methods are acceptable only if the AHJ approves them based on the conditions of use and any special requirements of the location [590.2(B)].

Article 590 addresses the electrical hazards of temporary installations. But other dangers include tripping hazards, spill hazards, and the hazards of things falling on people. You reduce most of these hazards through good housekeeping, which is an essential part of ensuring installations are safe.

For a limited time, only

Each temporary installation has time constraints, after which the temporary wiring must be removed. Here are the limits:

Construction period. You can use temporary electrical power and lighting installations during the construction, remodeling, maintenance, repair, or demolition of buildings, structures, equipment, or similar activities [590.3(A)].
Decorative lighting. You can supply temporary electrical power for decorative lighting for up to 90 days [590.3(B)].
Emergencies and tests. You can install temporary electrical power and lighting for emergencies, tests, or experiments for the duration necessary [590.3(C)].

You must remove temporary installations immediately upon the completion of the purpose for which you installed them [590.3(D)].

General requirements

About half of Art. 590 consists of 590.4, which provides requirements that apply to all temporary installations.

Services. Install temporary services so they meet the requirements of Art. 230. What this means is that a temporary service is installed in the same manner as a permanent service [590.4(A)].
Feeders. Open conductors are not allowed for temporary installations. Feeders are permitted in cable assemblies, including Type NM and Type NMC, hard usage cords, and extra-hard usage cords [590.4(B)], as shown in Fig. 1.
Branch circuits. The wiring methods allowed for feeders are also allowed for branch circuits, including Type NM and NMC cable exposed or concealed in any dwelling, building, or structure without any height limitation [590.4(C)], as shown in Fig. 2.

Receptacles. A receptacle must have a grounding terminal that is connected to an equipment grounding conductor per 250.146 and 406.3. On a construction site, temporary lighting and receptacles can’t be on the same branch circuit [590.4(D)], as shown in Fig. 3. This requirement ensures that the lighting circuit won’t be interrupted if the GFCI-protection device opens.

Disconnecting means. A suitable disconnecting means or plug connectors must be installed to permit the disconnection of all ungrounded conductors of each temporary circuit. Ungrounded conductors of a multiwire branch circuit must have a disconnecting means at the panelboard that opens all of the ungrounded conductors simultaneously. Individual single-pole circuit breakers with handle ties identified for the purpose can be used or a multi-pole circuit breaker with a common internal trip [590.4(E)]. See the definition of “Panelboard” in Art. 100. For additional multiwire branch-circuit requirements, see 210.4 and 300.13(B).
Lamp protection. The lamps used for temporary lighting must be afforded protection against damage from accidental contact by use of a suitable luminaire or lampholder with a guard. This is a safety measure provided to control a danger introduced by temporary lighting installations [590.4(F)].
Protection from accidental damage. Cables and flexible cords must be protected from accidental damage and from sharp corners and projections. Provide mechanical protection when cables and flexible cords pass through doorways or other pinch points [590.4(H)]. Solidly constructed cord guards are available for this purpose or any method approved by your AHJ [590.2(B)].
Support. Support cable assemblies and flexible cords at intervals that ensure protection from physical damage. Support must be in the form of staples, cable ties, straps, or other similar means designed not to damage the cable or cord assembly [590.4(J)]. The AHJ determines the support requirements for temporary cables, based on the job-site conditions [590.2(B)].
Vegetation. Vegetation is not allowed to support overhead spans of branch circuit or feeder conductors. Vegetation can be used to support listed decorative lighting when installed using strain-relief devices, tension take-up devices, or other AHJ-approved means to prevent damage to conductors from the movement of the live vegetation [590.4(J) Ex].

GFCI

Ground-fault current protection must be provided for all:

Temporary wiring that supplies power for construction, remodeling, maintenance, repair, or demolition of structures or equipment. It doesn’t matter whether that power comes from an electric utility or on-site generated power source [590.6], as shown in Fig. 4.

Receptacles rated 125V and 15A, 20A, or 30A, if used during construction, remodeling, maintenance, repair, or demolition of structures or equipment.

You can provide this protection with circuit breakers, receptacles, cord sets, or adapters that incorporate listed GFCI protection.

For all other receptacles that supply temporary power for the same kinds of activities, you can use GFCI protection or an assured grounding program [590.6(B)]. Assured grounding programs require rigorous enforcement [OSHA 1926.404(b)(1)(iii)], while simply providing GFCI protection for all temporary receptacles is an easier solution.

Avoid permanent mistakes

“Temporary” really does mean just that. Article 590 outlines the time limits that apply to temporary installations. Additional safety measures, such as using guards on lights, may be called for in temporary installations above what is required for permanent installations.

While temporary installation requirements may seem to offer some relaxation of certain installation standards, they will also facilitate rapid removal of temporary wiring when it is no longer needed. If you apply Art. 590 with safety in mind, you will be able to provide temporary installations with no permanent ill effects.