OSHA requirements are set by statute, standards and regulations. Our interpretation letters explain these requirements and how they apply to particular circumstances, but they cannot create additional employer obligations. This letter constitutes OSHA's interpretation of the requirements discussed. Note that our enforcement guidance may be affected by changes to OSHA rules. Also, from time to time we update our guidance in response to new information. To keep apprised of such developments, you can consult OSHA's website at https://www.osha.gov.

February 16, 1993

Mr. Philip P. Mercuris
Director of Safety
Master Builders of Iowa
221 Park Street
P.O. Box 695
Des Moines, Iowa 50303

Dear Mr. Mercuris:

This is in response to your December 22 letter requesting an interpretation of an Occupational Safety and Health Administration (OSHA) ground-fault protection for a construction job-site trailer.

With regard to whether GFCI's or an assured grounding conductor program is required for receptacles inside a construction job-site trailer, (reference National Electrical Code (NEC), Section 550-4), please be advised that although such trailers are permanently wired in accordance with the National Electrical Code still require, for certain interior receptacles, ground fault circuit interrupter protection for personnel (NEC Section 550-8(b)). However, as stated in your letter, all exterior receptacles and any interior receptacles used with cord sets running outside the trailer would not be considered a part of the permanent wiring. In such cases, either a GFCI or an assured grounding conductor program would be required in accordance to 29 CFR 1926.404(b).

If we can be of any further assistance, please contact me or Mr. Dale Cavanaugh of my staff at (202) 219-8136.


Roy Gurnham, P.E., Esq. Director
Office of Construction and Maritime
Compliance Assistance

December 22, 1992

Roger Clark
Director of Field Programs
U.S. Department of Labor OSHA
Francis Perkins Bldg.
Room N 3605
200 Constitution Ave. N.W.
Washington, D.C. 20210

Dear Mr. Clark:

Our contractors trade association, Master Builders of Iowa, is requesting an interpretation having to do with ground fault protection for a construction job-site trailer. For years contractors have used the electrical receptacles in a job trailer which is a part of the permanent wiring of a structure according to national electric code and manufacture specifications. These receptacles in trailers are used to run indoor appliances such as fax machines, adding machines, microwave, refrigerator and other misc. appliances.

The construction industry has always understood the OSHA Standard to say that permanent wiring of a structure did not need a GFCI until temporary wiring or temporary equipment was used. We do not know why all of a sudden OSHA is issuing citations for receptacles in this situation when they never have before and the OSHA Standard has not changed to indicate a citation. Just so you understand we do know the difference between temporary wiring and permanent wiring of a structure. We are in total agreement for the use of GFCI when electrical outlets are used outside of the trailer with flexible cords and power tools.

We do know that Iowa follows the federal OSHA standards and does not exceed the federal standard on this issue. A call was made to region seven in Kansas City. They agreed with us on this issue, however, if I wanted the interpretation in writing they suggested that I contact you. This is why we are writing for your interpretation. If you have any questions please call me at 800-362-2578 or 515-288-8904.

Thank you.


Philip P. Mercuris
Director of Safety
Master Builders of Iowa

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