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.

November 8, 1985

Mr. Raymond J. Callahan
Engineering Services
Robert Bosch Power Tool Corporation
3701 Neuse Boulevard
New Bern, North Carolina 28560-9399

Dear Mr. Callahan:

This is in response to your letter of September 25, concerning the Occupational Safety and Health Administration's (OSHA) policy on testing laboratory marking recognition, and regulations and policy of double insulated power tools.

As you may be aware, OSHA does not approve, certify, or endorse any product. OSHA would consider your product or any similar device acceptable for its intended purpose if it were accepted, certified, listed, labeled, or otherwise determined to be safe by a nationally recognized testing laboratory such as Underwriters' Laboratories, Incorporated, or Factory Mutual Engineering Corporation.

Portable electric tools specified as double-insulated are constructed with a special insulating system in lieu of a grounding means and must comply with the safety provisions of the National Electrical Code. Such equipment is identified by being distinctively marked. This marking consists of the double insulation symbol (a square within a square) and the words "double insulation" of the equivalent words "double-insulated."

In addition, the listing or labeling mark of a nationally recognized laboratory responsible for the product's safety evaluation must also be affixed to the tool and, together with the "double insulation" marking, completes the means for identifying double-insulated portable tools that are acceptable to OSHA. The definitions given in 1910.399 of Subpart S (copy enclosed) for determining the suitablilty of electrical utilization equipment and the extent to which such equipment is acceptable to the Assistant Secretary of Labor also apply to double-insulated tools.

As for the use of double insulated tools used with extension cords on construction sites, as they relate to out Ground Fault Protection Standards, the following information is offered.

The standard addresses two separate methods of ground-fault protection, of which the employer must choose one. If the ground-fault circuit interrupter (GFCI) option is chosen, all 120-volt, 15- and 20-ampere receptacle outlets, which are not part of the permanent wiring and which are in use by employees, must have approved ground-fault circuit interrupters form personnel protection regardless of the type of tools that are plugged into them. If the assured equipment grounding conductor program is the chosen option, then all cord sets, receptacles which are not part of the permanent wiring, and cord- and plug-connected equipment required to be grounded must be covered by the program. Although tools that are not required to be grounded (e.g., double insulated tools) have no equipment grounding conductor to be tested, the visual inspection of the attached cord and plug is still required. All other applicable requirements of the program however, apply to the extension cord and must be complied with for the protection of exposed employees. Specifically, these requirements include the following:

a. The employer must have a written description of his program;

b. One or more competent persons must have been designated to carry out the program;

c. No damaged or defective equipment shall be used;

d. The required tests must be performed; and

e. These tests must be recorded.

If we can be of further assistance, please let us know.


John B. Miles, Jr., Director
Directorate of Field Operations