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 14, 1982

Elmer Dupuis PE, CSP
United States Fidelity and Guaranty Company
Insurance Engineering & Audit Department
Thomas Jefferson Building 14 S. Fourth Street
St. Louis, Missouri 63102

Dear Mr. Dupuis:

Thank you for your letter of January 28, 1982, regarding construction electrical safety.

In the construction standard used by OSHA, section 1926.400(a) adopts the 1971 National Electrical Code by reference. Section 445-8 of the 1971 NEC requires grounding the frame of any generator producing more than 150 volts. Generators producing lower voltages are not required to have their frames grounded, as long as the frame is insulated from ground.

Section 250-45 of the 1971 NEC and section 1926.401(a) require hand-held, motor-operated tools to be grounded or double-insulated. This requirement applies regardless of whether the generator to which they are connected is grounded. If the frame is grounded, the equipment grounding conductor must be bonded to it. If the generator frame is ungrounded, the equipment grounding conductor for the tools must be connected to ground separately.

Our policy, as stated in OSHA Directive No. CPL 2.11A (copy enclosed), is to accept installations made in accordance with later editions of national consensus standards adopted by reference. In this case, we would accept an installation made following the requirements of the 1981 NEC in place of the 1971 NEC. Section 250-6 (copy enclosed) of the 1981 NEC addresses portable and vehicle-mounted generators. The requirements are straightforward. In brief, they allow the generator frame to be ungrounded and allow the equipment grounding conductor to be bonded to the frame of the generator in lieu of ground.

In regards to your last question, it is recommended that you contact the manufacturer to obtain an answer directly.

Should you have any further questions, please do not hesitate to call or write.


John K. Barto
Division of Occupational Safety Programming