Protective grounding for underground electrical work

December 7, 1995

Mr. Andrew J. Woodacre
Brotherhood of Utility Workers of New England, Inc.
[Recipient address omitted]
Dear Mr. Woodacre:

This is in response to your August 24 letter to Mr. John T. Phillips, Administrator of Region I in the Occupational Safety and Health Administration (OSHA). Your letter was forwarded to this directorate for response. Please accept our apology for the delay in responding. Your question and our reply follow applicable information (provided in you letter) which is reiterated below.

Information: The following descriptions are applicable to the two diagrams (See the enclosed copies) that you provided.

"Description of Typical Underground Circuit (Diagram 1)

The attached diagram typifies a 3 phase, 15 kV city underground circuit. The conductor size ranges from 4/0 to 500 MCM Copper. The "T" taps (marked X-Z) are "T" splices located in manholes. At each switch location (marked A-E) there is a potential source.

Commonwealth's Switching, Grounding, and Tagging Procedure for Work Location W (Diagram 2)

Work location W is in a manhole with no means of grounding the conductors to be cut. The distance between "T" tap Z and switch A is no greater than 1000 feet.

• All switches are opened, live line tested, and red tagged.

• Three phase working grounds are installed at locations A and B. The grounds are Commonwealth's standard grounds made up of No. 2 AWG. copper conductors minimum and are connected phase to phase to ground."

Question: If a person was working at location W, would it be necessary for grounds to be applied at locations A,B,C,D, and E?

Reply: You have not provided sufficient information (See the following paragraph of this reply) to determine whether the placement of grounds at all the locations indicated would be needed to provide for employee safety as required under paragraphs 1910.269(m) and (n).

Under paragraph 1910.269(m)(3)(vi), protective grounds must be installed as required by paragraph 1910.269(n). Paragraph 1910.269(n)(3) requires temporary protective grounds to be placed at such locations and in such a manner as to prevent each employee from being exposed to hazardous differences in electrical potential. To comply with this grounding standard, an employer must determine the maximum voltage to which an employee would be exposed in the event the line on which he or she is working becomes energized. Generally, this will require a fault current analysis, with the personal protective grounds representing faults. The calculated fault voltage at the work location (W) would indicate whether a specific grounding arrangement would protect each employee. Conducting tests to determine actual fault voltages is an alternative method of determining compliance.

If we can be of further assistance, please contact Mr. Ronald J. Davies of my staff, telephone (202) 219-8031, extension 110.

Sincerely,

John B. Miles, Jr.,
Director Directorate of Compliance Programs