NM Cables Installed in Temporary Installations

Article 305 for temporary wiring in the 1999 National Electrical Code has been relocated to Article 527 covering temporary installations in the 2002 NEC. At first glance, relocating an article from Chapter 3 to Chapter 5 would appear to be a subtle change with little effect on temporary installations. However, this change does affect the use of NM cable as a temporary wiring method.

To understand the overall effect, the arrangement of the NEC must first be understood. Chapters 1 through 4 apply generally to all installations, while Chapters 5, 6 and 7 can specifically supplement or modify the general requirements in Chapters 1 through 4. Chapter 5 covers special occupancies, Chapter 6 covers special equipment, and Chapter 7 covers special conditions. Article 527 (former Article 305) can modify or supplement the information found in the first four chapters, especially concerning wiring methods found in Chapter 3.

Article 527 applies to installations where temporary electrical power and lighting is necessary during periods of construction, remodeling, maintenance, repair or demolition of buildings, structures, equipment or similar activities. The temporary installation of power and lighting must comply with all of the applicable requirements of the NEC, except as specifically modified by Article 527.

Section 527.4(B) requires feeders to be protected in accordance with Article 240. Feeders must originate in an approved distribution center, such as a switchboard or panelboard. Existing switchboards or panelboards are often used to supply power to feeders on a temporary basis until the permanent distribution system is installed. If an existing distribution system is used for temporary power, all safety procedures must be strictly followed and care must be taken so no live parts are accessible to unauthorized persons at the site.

Hard-usage or extra-hard-usage multiconductor cords or cables identified in Table 400.4 are permitted for temporary feeders. Open individual conductors, as described in Section 310.13, are only permitted for use as temporary feeders during emergencies and for tests, experiments and developmental work. Open individual conductors can be installed as a cable assembly or in a raceway system.

Temporary branch circuits must comply with Article 240 and must originate in an approved power outlet or panelboard with an appropriate branch circuit overcurrent protective device protecting the circuit. Multiconductor cords or cables may be used for temporary branch circuits where identified as hard usage or extra-hard usage in Table 400.4. Cable assemblies may also be used for branch circuits to provide temporary power for receptacles and lighting.

An exception permits single-insulated conductors to be used for holiday decorative lighting based upon a maximum period of 90 days in accordance with 527.3(B) or for emergencies, tests, experiments or developmental work in accordance with 527.3(C).

Where single insulated conductors are used for holiday lighting, the voltage to ground must not exceed 150V, the wiring must not be subject to physical damage, and the conductors must be supported on insulators at intervals not greater than 10 feet. If festoon lighting is used for temporary holiday lighting, the individual conductors must be arranged so excessive strain is not transmitted to the lampholders.

The subtle change that occurred in relocating Article 305 to Article 527 involves the use of Type NM or NMC cable for temporary feeders and branch circuits. Sections 527.4(B) and (C) permit Type NM and Type NMC cables to be used in any dwelling, building or structure without any height limitation for temporary feeders and branch circuits. Section 334.10 permits NM and NMC cable to installed in multifamily dwellings of Types III, IV and V construction, except as prohibited in 334.12.

NM and NMC Cables are permitted to be installed in other structures of Types III, IV and V construction, except as prohibited in 334.12. However, these cables can only be installed in these other structures where concealed within walls, floors or ceilings that provide a thermal barrier of material with at least a 15-minute finish rating as identified in listings of fire-rated assemblies.

Therein lies the problem. Since neither 527.4(B) nor (C) modify or amend this requirement, NM or NMC used for temporary branch circuits or feeders in structures other than one- and two-family dwellings and multifamily dwellings must be concealed within the walls, ceilings or floors with a 15-minute finish rating. A Tentative Interim Amendment has been issued for the 2002 NEC amending this requirement for temporary branch circuits and feeders installed in other buildings, thus permitting NM or NMC cables to be installed as temporary wiring in buildings of any height without the restriction of the 15-minute finish rating.

Remember, based on Section 110.2, the authority having jurisdiction always must approve all wiring methods, including those used for temporary installations. Providing the utmost safety for a temporary installation is imperative. EC

ODE is staff engineering associate at Underwriters Laboratories Inc., in Research Triangle Park, N.C. He can be reached at 919.549.1726 or via e-mail at mark.c.ode@us.ul.com.


About the Author

Mark C. Ode

Fire/Life Safety Columnist and Code Contributor
Mark C. Ode is a lead engineering associate for Energy & Power Technologies at Underwriters Laboratories Inc. and can be reached at 919.949.2576 and Mark.C.Ode@ul.com .

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