February 23, 1999

T. Michael Toole, Ph.D., P.E.
Director of Construction Systems
Packer Engineering, Inc.
1950 North Washington Street
P.O. Box 353
Naperville, Illinois 60566-0353

Re: 29 CFR 1926.416(a); whether plastic conduit sheathing is insulation; definition of insulation

Dear Dr. Toole:

This is in response to your letter dated May 1, 1998, to the Occupational Safety and Health Administration (OSHA) requesting clarification of the term "insulation" as used in 29 CFR 1926.416(a).

Definition of insulation

The first part of that standard states:

(1) No employer shall permit an employee to work in such proximity to any part of an electric power circuit that the employee could contact the electric power circuit in the course of work, unless the employee is protected against electric shock by deenergizing the circuit and grounding it or by guarding it effectively by insulation or other means [emphasis added].

The term "insulation," as used in this provision, means a material that will protect employees from shock hazards associated with electrical power circuits. Factors such as use and location will determine the proper type of conductor insulation required. Insulation integral to conductors must withstand exposure to atmospheric and other conditions of use without detrimental leakage of current.

Whether plastic sheathing is considered insulation

You also ask about a situation in which a "circuit" has "plastic sheathing over the conductor" and is not in any type of rigid conduit. You ask if "the plastic sheathing over the conductor [would] be considered insulation" under §1926.416(a).

In most 120 volt and 240 volt circuits, current is carried through two of three circuit conductors. One is ungrounded and one is neutral.¹ An equipment grounding conductor is also usually included in the cable. The two circuit conductors are made of solid or stranded conducting material -- wire. Each wire is encased in insulating material. The equipment grounding conductor is normally either bare wire or wrapped in paper. The two insulated conductors, plus the equipment grounding conductor, are collectively encased in either a flexible plastic sheath or a flexible metal sheath.

We assume that when you use the term "conductor" in your question, you are referring to the current carrying conductors (consisting of wire individually encased by insulating material), plus the equipment grounding conductor. We further assume that when you refer to the "plastic sheathing over the conductor," you are referring to the typical plastic sheath that collectively encases the insulated conductors plus the grounding conductor. In that circumstance, the plastic sheathing that holds the conductors plus the equipment grounding conductor is not designed to serve as insulation. While it may or may not have some insulating properties, its purpose is to (1) conveniently package the three conductors into one cable, (2) provide protection against atmospheric and other conditions of use without detrimental leakage of current and (3) protecting the conductors -- both the wires and the insulation that encases them, as well as the equipment grounding conductor -- from mechanical damage.

Guarding against electric shock

You ask if the term "insulation," as used in 1926.416(a), refers only to the insulating material that encases a wire, or if the term refers to "a separate insulating system worn or used by the workers?"

Where a circuit has not been deenergized, section 1926.416(a) requires that employees be protected from electric shock by "guarding it [the circuit] effectively by insulation." This means that the employer must ensure that insulation already covers the energized parts and will protect the employee. That insulation must be sufficient/appropriate for the working conditions. If it will not protect the employee, then the employer must use insulating material, such as an insulating blanket, to protect against the shock hazard. Where that is not feasible, this provision, in conjunction with §1926.95(a), requires employers to protect employees with appropriate insulating personal protective equipment.²

If you require any further assistance, please do not hesitate to contact us again by writing to: Directorate of Construction - OSHA Office of Construction Standards and Compliance Assistance, Room N3621, 200 Constitution Avenue N.W., Washington, D.C. 20210.

Sincerely,

Russell B. Swanson, Director
Directorate of Construction

Footnote (1) In a solidly grounded neutral system, the neutral conductor is also called the grounded conductor. (Back to text)