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.

October 1, 1991

Mr. Colin Iwasa
OPE Product Coordinator
Yamaha Motor Corporation
6555 Katella Avenue
Cypress, California 90630

Dear Mr. Iwasa:

This is in response to your August 14, 1991, letter requesting clarification of the Occupational Safety and Health Administration's (OSHA) electrical standards pertaining to portable generators.

In regard to your question whether portable or vehicle mounted generators on a job site are required to be listed, labeled or certified, please be advised that OSHA has no such requirement. However, paragraph (a) of 29 CFR 1926.403 requires all electrical conductors and equipment to be "approved". OSHA has determined that equipment listed, labeled, or certified to be safe by a qualified testing laboratory, is considered to be "approved". (A copy of 29 CFR 1926, Subpart K is enclosed. Please see the definitions of "acceptable" and "approved".)

In regard to your question whether a 120/240 volt portable generator rated at 5000 watts is required to have the neutrals bonded, please be advised as follows: A neutral conductor shall be bonded to the generator frame when the generator is a component of a separately derived system. (See 29 CFR 1926.404(f)(3)(iii)). Thus, where the generator supplies only equipment mounted on the generator and/or cord- and plug-connected equipment through receptacles mounted on the generator and the noncurrent-carrying metal parts of equipment and equipment grounding conductor terminals of the receptacles are bonded to the generator frame, then the portable generator frame is not required to be grounded and is permitted to serve as the grounding electrode. (See 29 CFR, 1926.404(f) (3)(i)). However, portable generators supplying fixed wiring systems are not generally considered to be separately derived systems and usually have to be grounded. An alternating-current power source such as an on-site generator is not a separately derived system if the neutral is solidly interconnected to a service-supplied system neutral. In such cases, the neutral conductor of a single-phase, 3 wire system must be grounded. (See 29 CFR 1926.404(f)(1),(4), and (5)).

If we can be of further assistance, please contact Mr. Roy Gurnham, Director, Office of Construction and Maritime Compliance Assistance, phone (202) 523-8136.


Patricia K. Clark, Director
Directorate of Compliance Programs