Ezel / Labor Guidance / US
Back to Federal guidance

Protecting flexible cords in tunnel shafts

Summary An OSHA area office asked about type SO flexible electrical cords in tunnel shafts. OSHA said the cord's own insulation does not protect against heavy-object damage such as a muck bucket strike, so the cord must be moved or physically shielded. It said the cord may run with other tunnel utilities if mechanical protection prevents insulation damage from energizing those systems.
Document
Federal opinion letter
Agency
Occupational Safety and Health Administration (OSHA)
Document number
1991-07-08
Date issued
July 8, 1991
Status
Active
Status last verified October 9, 2026
Topics
Workplace Safety OSHA 1926 Electrical Safety Construction
Source
View the official document

Apply this to your situation

This page explains the general guidance. Ask about your specific situation and see what current federal labor law says, with citations.

About this page: The full text below is the official document from Occupational Safety and Health Administration (OSHA). Ezel adds the plain-English summary and tracks the document's status. The official source linked on this page is authoritative for any reliance.

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.

Related guidance

Permanently labeled locks for electrical lockout Opinion Letter · August 17, 2026 Helmet selection for lateral head-impact hazards Opinion Letter · August 17, 2026 Asbestos precautions when restoring drywall after flood damage Opinion Letter · May 7, 2026 Enforcement policy for recording and reporting COVID-19 cases Guidance · March 31, 2026

What does federal law require in your situation?

Ezel checks current federal labor law against your facts and answers with citations.

Opens in Ezel Pro.

  • Checks the law as it stands today, not only this page
  • Cites every source it relies on, so you can verify it
  • Chat, drafting and research in one workspace