April 25, 2006
Mr. Michael L. Harbaugh
909 Adams Street
Great Bend, KS 67530
Dear Mr. Harbaugh:
This is in response to your January 5, 2006, letter requesting interpretation of the Occupational Safety and Health Administration (OSHA) rule at 29 CFR 1910.269, Electric power generation, transmission, and distribution. This letter constitutes OSHA's interpretation only of the questions raised, and may not be applicable to any issues not delineated within your original correspondence. Your paraphrased scenario, questions, and our responses are provided below.
Scenario: A qualified power line worker is performing work on the secondary side of a 7200/12470-volt - 120/240-volt pad-mounted transformer. His job is to install a secondary service wire onto the secondary 120/240-volt side of the transformer. This job will take place with both the primary and secondary sides of the transformer energized. The secondary conductor has a 600-volt insulation rating on the conductor. The primary elbows and conductors are insulated for the voltage involved. Given the configuration of a typical pad-mounted transformer, there are approximately 11 inches of clearance between the secondary 120/240-volt terminations and the primary 7200/12470-volt elbows on the transformer. Also, there is primary cable that is either in contact with or in very close proximity to the secondary conductors inside the cabinet. Further conditions are that the primary elbows and conductors are considered to be dead-front. In other words, the primary elbows and conductors have insulation rated for the voltage involved.
Question : Does OSHA consider the insulation on direct buried underground primary cable and elbows as providing insulation for the protection of the worker while working inside an underground pad-mounted transformer?
Response: OSHA's standard at 29 CFR 1910.269(l)(2) contains requirements for employees working on or near energized exposed parts. Specifically, paragraph .269(l)(2) of this section requires employers to:
... ensure that no employee approaches or takes any conductive object closer to exposed energized parts than set forth in Table R-6 through Table R-10, unless:
(i) The employee is insulated from the energized part (insulating gloves or insulating gloves and sleeves worn in accordance with paragraph (l)(3) of this section are considered insulation of the employee only with regard to the energized part upon which work is being performed), or
(ii) The energized part is insulated from the employee and from any other conductive object at a different potential, or
(iii) The employee is insulated from any other exposed conductive object, as during live-line bare-hand work.
Typically, direct buried underground cable and elbows are designed with insulation sufficient for the voltage involved. This cable's design specification normally provides insulation meeting the insulation requirements of paragraph .269(l)(2)(ii). You must note, however, that insulation may degrade over time to a point where it may no longer meet the design specifications for the voltage involved. In such situations, an employer would not be able to rely on the insulation of the cable to meet the requirements of paragraph .269(l)(2).
Additionally, the integrity of the concentric neutral and its drain-wire connection at the tie-off tab on the elbow can pose a voltage hazard to the employee. The strand wires that form the concentric-neutral outer wrap and the drain wire are unprotected and vulnerable to oxidation; thus, there is no assurance that the exposed surface of the load-break elbow is at ground potential, or zero volts. Consequently, OSHA generally considers the elbow as not safe to touch with bare hands, and the employee would have to maintain a minimum approach distance of "avoid contact."1
Question : Given the scenario identified above, the lineman's upper arms would be within 2 feet 1 inch (the minimum approach distance) of the insulated primary elbow and conductor while work is being performed on the secondary side of the transformer. Therefore, is the lineman who is going to be working on the secondary side of the pad-mounted transformer required to wear rubber sleeves in conjunction with rubber gloves while performing the work on the secondary side of the transformer?
Response: Paragraph (l)(3) of §1910.269 applies to your scenario. Under this provision, the employee need not wear rubber insulating sleeves as long as all energized parts on which the employee is not working are adequately insulated. In general, power line worker working on a secondary side of the transformer need not wear rubber insulating sleeves, as long as: (1) the primary side conductors and elbows are designed and maintained with insulation sufficient for the voltage; (2) the concentric neutral wire is not corroded and its connection at the tie-off tab on the elbow is intact (which would ensure that this part is at ground potential); and (3) the only exposed energized part on the secondary side is the one on which the employee is working.
Question : What voltage level does the lineman have to be protected to — 120/240 or 7200/12470 volts, when working on 120/240-volt secondary side of the transformer? (There will be no intentional physical contact with the primary side of the transformer.)
Response: To the extent the insulation on the primary cables is sufficient as indicated in the response to your first question, then the rubber insulating gloves would have to be rated for use on the secondary voltage.
Thank you for your interest in occupational safety and health. 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 http://www.osha.gov. If you have any further questions, please feel free to contact the Office of General Industry Enforcement at (202) 693-1850.
Richard E. Fairfax, Director
Directorate of Compliance Programs
1 Manufacturers' instructions for insulated plug-in terminations or elbows that are used for connecting underground cables to transformers, switching cabinets, and junction boxes require attachment of a ground wire to maintain dead front safety. Generally, this is accomplished for underground distribution cable installations by connecting a wire strand from the concentric neutral outer wrap. Over time, the integrity of this connection may be jeopardized by a number of conditions, including high atmospheric moisture content, salt water or other corrosive atmospheres, a shift in the position of the equipment, or a movement of the cables. If the integrity of the ground path is compromised, then there is no positive assurance that the outer surface of the elbow connector is at ground potential, or zero volts. Without a proper connection at the elbow's grounding tab, the voltage can be as high as the system's phase-to-ground voltage, or 7,200 volts in your scenario. Table R-6 of section 1910.269 minimally requires avoiding contact for voltages ranging from 50 to 1,000 volts, and it is reasonable to assume the presence of voltage in this range, if the integrity of the grounding connection is not assured. [ back to text ]