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.

July 8, 1991

MEMORANDUM FOR:     DAVID GRAFTON

                   SOUTH BOSTON AREA OFFICE

THROUGH:            CHARLES CULVER, Director 
                   Office of Construction and Engineering

FROM:               PATRICK FINN, Chief of Construction
                   Division Office of Construction and Engineering

SUBJECT:            PROTECTION OF FLEXIBLE CORDS WHEN HUNG IN TUNNEL SHAFTS

In response to your telephone conversation with Bill Burke of this office concerning the use of type "SO" flexible cords in tunnel shafts, OSHA standard 29 CFR 1926.405(a)(2)(ii)(I) states "Flexible cords and cables shall be protected from damage". Type "SO" flexible cords must be protected from physical damage when mounted on the inside of a tunnel shaft. The insulation on type "SO" flexible cords is not suitable protection against physical damage when the flexible cord is subject to being struck by heavy objects. The raising and lowering of the muck bucket through the shaft opening could create this condition. Type "SO" Flexible Cord should be located outside of the shaft, concealed behind "H" piles, or physically protected in another fashion to limit the possibility of damage to the cord's insulation and subsequent energizing of other conductive material. Although "SO" flexible cords are suitable for hard and extra hard usage, these cords were not manufactured to withstand this type of abuse.

Regarding your concern about running type "SO" flexible cord with utilities in tunnel work, this is permitted under 29 CFR 1926.800(s)(1) if adequate mechanical protection is provided to assure the integrity of the cord's insulation and in such a fashion that any inadvertent damage to the cord's insulation will not result in energizing of other utility systems.

If you have any further questions concerning the use of type "SO" flexible cords in tunnel shafts, you may contact Bill Burke at FTS 523-1440.