Double-insulated tools and ground-fault protection

October 7, 1977

MEMORANDUM FOR: CARLYLE BUNN, Acting Assistant Regional Administrator for Technical Support
THRU: DONALD E. MACKENZIE, Field Coordinator
FROM: RICHARD P. WILSON, Deputy Director, Federal Compliance and State Programs
SUBJECT: Double-Insulated Tools and Ground-Fault Protection on Construction Sites

This is in response to your letter dated August 5, 1977, on the above subject.

The ground-fault protection standard requires the employer to provide either ground-fault circuit interrupters (GFCI's) or an assured equipment grounding conductor program to protect employees on construction sites. If the employer has chosen the GFCI option, he must use them to protect his employee whether grounded or double-insulated tools are used. If the employer uses the assured equipment grounding conductor program, he must comply with all the provisions given under that option. However, double-insulated tools do not require the equipment grounding conductor tests, since they are not required to be grounded.

The exposure to ground-fault hazards exists when any electric tool is being used even on a grounded circuit. Specifically, a shock hazard develops with the use of a double-insulated tool under the following conditions (among others):

1. When the tool is immersed in water;

2. When the tool is abused and the internal double insulation is bridged; and,

3. When defects develop in the supply cord of the tool.

I hope this information will be helpful.