Only Temporary

Recent discussions on ground-fault circuit interrupter (GFCI) protection for personnel on construction sites have indicated that there seems to be a misunderstanding of whether generator power is excluded from the GFCI requirement. A thorough understanding of the history, origin and present requirements for GFCI protection may clear up any misunderstandings.

The original purpose for providing GFCI protection for temporary receptacles on construction sites and other similar locations was to ensure the safety of any personnel using electrical receptacles to supply power to various electrical appliances.

Ground-fault circuit interrupters are designed with the load-side conductors passing through a differential comparison network. If the current in both load-side conductors is equal, the circuit functions normally. If there is an imbalance between the two conductors of more than 4 to 6 milliamps, the differential comparison network will trip the device. The trip time or time-current characteristic of a GFCI is about 25 milliseconds or about one 40th of a second providing protection against electrocution.

Construction sites require extra care since the potential for damage to conductors, equipment and portable appliances is much greater than other installations. Moisture and improper maintenance of electrical equipment can cause potential hazards that a GFCI-protected circuit will help protect against.

Ground-fault circuit interrupter protection for receptacles on construction sites was inserted into the 1971 National Electrical Code (NEC) as a new third paragraph in Section 210-7 with an effective enforcement date of Jan. 1, 1974.

The new section required GFCI protection for “all 120-volt single-phase, 15- and 20-ampere receptacles that were not part of the permanent wiring of the building or structure.” There was an exception permitting exclusion of GFCI protection for receptacles on portable or vehicle-mounted generators rated not more than 5 kilowatts (kW).

This section was moved to Section 210-8(b) in the 1975 NEC with the exception not requiring GFCI protection on generators worded as follows: “Receptacles on a portable generator rated not more than 5 kW, where the circuit conductors of the generator are insulated from earth and the generator frame is insulated from earth and all grounded surfaces.”

This text was subsequently changed by a Tentative Interim Amendment (TIA) between the 1975 NEC and the 1978 NEC to read: “Receptacles on a portable or vehicle mounted generator rated not more than 5 kW, where the circuit conductors are insulated from the generator frame as permitted in Section 250-6.”

This TIA changed the text so the generator did not have to be insulated from earth and all grounded surfaces, allowing it to sit on the ground or near a grounded object.

The text in the 1978 NEC was expanded to read as follows: “All 120-volt single-phase, 15- and 20-ampere receptacle outlets which are not part of the permanent wiring of the building or structure, and which are in use by employees shall have ground-fault circuit-interrupters for personnel protection.”

A new Exception No. 2 was added to 210-8(b) permitting written procedures called the “Assured Equipment Grounding Conductor Program” where continuity testing of electrical equipment, flexible cord sets and any fixed receptacles can be used in lieu of GFCI protection. The text in Section 210.8-(b) was moved to Section 305-4 covering temporary wiring in the 1984 NEC as a more appropriate location for GFCI protection on construction sites and in 1987 the text was relocated to 305.6.

In 1993, the original text in the base requirement for GFCI protection on construction sites was amended to require GFCI protection for receptacles that are part of the permanent wiring of the building or structure where the receptacle is used for temporary power. In 1996, this section was amended to permit cord sets incorporating listed GFCI protection to be used. This change recognized the use of personal GFCI devices that could be worn on an individual, rather than requiring the receptacles on the job site to be GFCI protected.

In the 1999 NEC, GFCI requirements for 30-ampere 125-volt single-phase was added to the 15- and 20-ampere receptacle requirement. Also added was the requirement that all receptacles rated more than 125-volt, 15-, 20-, and 30-amperes must be GFCI protected or follow the “assured equipment-grounding conductor program.”

In the 2002 NEC, Article 305 on Temporary Wiring was relocated to new Article 527 and renamed “Temporary Installations” and then again relocated into new Article 590 in the 2005 NEC.

The exception permitting 5 kW and smaller generators to exclude GFCI protection was also deleted. By deleting the exception, all power supplying 125-volt, single-phase, 15-, 20- and 30-ampere receptacles for temporary power to equipment used by personnel during construction, maintenance, repair or demolition of buildings, equipment or similar activities, including power supplied from a generator, must be GFCI protected. EC

ODE is a staff engineering associate at Underwriters Laboratories Inc., in Research Triangle Park, N.C. He can be reached at 919.549.1726 or at




About the Author

Mark C. Ode

Fire/Life Safety, Residential 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

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