Note: This article references the 2017 NEC because the Philadelphia area — the jurisdiction where this author teaches and works— is still operating under that version of the Code.
As you progress in your electrical career as an electrical apprentice, it’s vital to grasp the guidelines for one of the most critical phases of a construction project — the building stage. As a job-site electrician, one day you may be responsible for ensuring that all construction teams on a project have the necessary power distribution and lighting for their power tools, machinery, and equipment. Whether the energy comes from the local electric utility or portable generators on or near the job site, understanding the provisions and guidelines set by Art. 590 is essential for your future roles.
This Article applies to buildings, structures, equipment, or similar activities during repair, demolition, remodeling, maintenance, or the “period of construction.” It's essential to follow the guidelines in Art. 590 as well as your company's individual safety policy and protocols to:
- Satisfy any requirements of the company's insurer.
- Abide by any local construction ordinances for “temp power.”
- Avoid hefty fines set by governmental agencies like OSHA.
- Ensure the safety of all construction teams, vendors, and job-site visitors.
Installing the service, feeders, or overcurrent devices
As noted in Sec. 590.4, keep in mind the rules and guidelines of Article 230 (Services) still apply to your temp service, specifically Parts I through VIII. Follow these overcurrent guidelines provided in Art. 240 for your feeders:
- Protection of conductors (Sec. 240.4)
- Feeders and branch circuits (Sec. 240.100)
- Additional requirements for feeders (Sec. 240.101)
- Protection of flexible cords, flexible cables, and fixture wires (Sec. 240.5)
The most important rule
To comply with Sec. 590.6(A) and (B), ground-fault protection for personnel must be provided for all temporary wiring installations used to supply power to equipment used by personnel; this rule applies to power derived from an electric utility company or from an on-site-generated power source.
Ground-fault circuit-interrupter (GFCI) protection for personnel shall be provided for all 125V, single-phase, 15A, 20A, and 30A receptacle outlets installed or existing as part of the permanent wiring of the building or structure and used for temporary electric power. Listed cord sets or devices incorporating listed GFCI protection for personnel identified for portable use shall be permitted per Sec. 590.6(B).
Permitted wiring methods for branch circuits and feeders
For the purposes of Sec. 590.4(B), use conductors within Table 400.4 that are identified as "hard usage" or "extra-hard usage" cords, multiconductor cords, and cable assemblies. Here are additional wiring methods permitted: Type NM (Art. 334); Type NMC (Art. 334); and Type SE (Art. 338). Note: Type SE cable shall be permitted to be installed in raceways in an underground installation.
Terminations at devices utilizing flexible cords and cables entering enclosures containing devices requiring termination shall be secured to the box with fittings “listed” for connecting flexible cords and cables to boxes designed for the purpose and use per Sec. 590.4(I). Cables and conductors shall not be concealed in floors, ceilings, or within walls.
Single insulated conductors shall be permitted where installed for the purpose and during emergencies and for tests, experiments, and developmental work, where accessible only to qualified persons.
Remember to always check permitted uses first. Ultimately, the wiring you use to distribute power and lighting must be "approved" for that specific use and environment. Temporary wiring methods shall be acceptable only if approved by the county or an independent third-party electrical inspector. The cables and conductors you use should be based on environmental conditions, use, and any special requirements for the temporary installation. Always check your "uses permitted" in the Part 2 "Installations" sections of Chapter 3 for wiring methods during this phase.
Time is of the essence
Always keep in mind the time limits set by Sec. 590.3(B) as well. Temporary power installations are permitted for a period "not exceeding" 90 days for holiday decorative lighting and similar purposes. If your project extends beyond 90 days, you may need a more permanent or durable wiring method.
Avoid redoing your temp power installation. Electrical permits and temp wiring have a specific time duration to be considered valid (check with the county office) based on Art. 590. You can also use temp power installations during emergencies and for tests, experiments, and developmental work. However, temporary wiring must be removed immediately upon completion of construction or the purpose for which the wiring was installed, as noted in Sec. 590.3(C).
Installation rules for branch circuits and receptacles
All branch circuits shall originate in an approved switchgear, panelboard, switchboard, power outlet, motor control center, and fused switch enclosure. And keep in mind the branch circuit exception located in Sec. 590.4(C)(2). Where the wiring is installed in accordance with 590.3(B):
- The voltage to ground shall not exceed 150V.
- The wiring shall not be subject to physical damage; it shall be protected per Sec. 590.4(H). Flexible cords and cables shall be protected from accidental damage. Sharp corners and projections shall be avoided. Where passing through doorways or other pinch points, protection shall be provided to prevent damage.
- The conductors shall be supported on insulators at intervals of not more than 10 ft; for festoon lighting, the conductors shall be so arranged that excessive strain is not transmitted to the lampholders.
Installing job-site receptacles
All receptacles shall be of the grounding type unless installed in a continuous metal raceway that qualifies as an equipment grounding conductor in accordance with Sec. 250.118, such as: rigid metal conduit (RMC) — Art. 344; electrical metallic tubing (EMT) — Art. 358; intermediate metal conduit (IMC) — Art. 342; or a continuous metal-covered cable that qualifies as an equipment grounding conductor in accordance with Sec. 250.118, which states: The equipment grounding conductor run with or enclosing the circuit conductors shall be one or more or a combination of the following: a copper, aluminum, or copper-clad aluminum conductor.
This conductor shall be solid or stranded, insulated, covered, or bare, and in the form of a wire or a busbar of any shape. All branch circuits shall include a separate equipment grounding conductor and all receptacles shall be electrically connected to the equipment grounding conductor(s). Receptacles on construction sites shall not be installed on any branch circuit that supplies temporary lighting, as explained in Sec. 590.4(D). All 15A and 20A, 125V and 250V receptacles installed in a wet location shall comply with Sec. 406.9(B)(1).
To learn more about navigating Chapter 3 and the permitted uses of wiring methods, check out my past articles on “The Apprentice’s Guide to MC-Type Cable,” “The Apprentice’s Guide to Non-Metallic Sheathed Cable,” and “The Apprentice’s Guide to Service Entrance Cable.”
For more information on flexible cables, assemblies, and Chapter 4 requirements, read my past columns on “The Apprentice’s Guide to Everyday Electrical Equipment,” “The Apprentice’s Guide to Article 640,” and “The Apprentice’s Guide to Article 300.”
