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 http://www.osha.gov.



June 12, 2000

Hilti Entwicklung Elektrowerkzeuge GmbH
z. Hd. Axel Fischer
Hiltistrasse 6
D-86916 Kaufering

Dear Mr. Fischer:

This responds to your January 31, 2000, e-mail to the Occupational Safety and Health Administration (OSHA), in which you ask the following questions related to electrical power tools for construction. Please accept our apology for the delay in responding to this inquiry.

Question 1: Must electric power tools be either "double insulated" (class II, plug without grounding prong) or grounded?

Answer: Yes, but there are some limitations to choosing the double insulation option. 29 CFR 1926.404(f)(7)(iv) states that electric power tools must be grounded except when they are double insulated. The standard allows double insulation instead of grounding within certain limitations — double insulated tools are not to be used in a hazardous location and must not to be operated at over 150 volts to ground. Also, double insulated tools must be distinctively marked.

Note: Class designations in the standard for electric equipment refer to suitability for use in a hazardous location. Your e-mail indicates that your equipment is not intended to be used in a hazardous location.

Question 2: Must electrical power tools be approved by an Nationally Recognized Testing Laboratory?

Answer: Yes. Under §1926.403(a), all electrical conductors and equipment must be "approved." The standard defines approved as "acceptable." With regard to your equipment, acceptable means "accepted, or certified, or listed, or labeled, or otherwise determined to be safe by a qualified testing laboratory capable of determining the suitability of materials and equipment for installation and use in accordance with this standard." See §1926.449.

Question 3: Must receptacles used for the connection of electric motors be limited to a maximum rating of 15-ampere per branch circuit?

Answer: Under §1926.404(b)(2)(iii), the rating of the receptacle that you would have to use is governed by two requirements: (1) the rating of a receptacle used for cord-and-plug connection of a motor to a branch circuit must not exceed 15-ampere at 125 volts or 10-ampere at 250 volts if individual overload protection is omitted; (2) even if individual motor overload protection is provided, the maximum rated receptacle that is permitted to be used on the circuit must conform to Table K-4 in §1926.404(b)(2)(iii) [see below]. Therefore, the answer depends first on whether individual motor overload protection is provided. If it is provided, then whether you can use a receptacle rated at more than 15-ampere will depend on the rating of the circuit (see Table K-4).

Where there is no individual motor overload protection, you are prohibited from using a receptacle with a rating over 15-ampere. However, where individual motor overload protection is provided, there are circumstances where a receptacle rated more than 15-ampere could be used. For example, (where individual motor overload protection is provided), a receptacle rated at 20 ampere could be used on a circuit rated at 20 ampere.



Circuit rating ampere Receptacle rating ampere
15...................................... Not over 15.
20...................................... 15 or 20.
30...................................... 30.
40...................................... 40 or 50.
50...................................... 50.


Question 4: Can electric power tools with a 20 ampere "Twist Lock" Plug be used on a 15 ampere standard receptacle by the means of an adapter if the rated power of the electric power tool (when energized) does not exceed 15-ampere?

Answer: There would be several problems with using an adapter on a tool that draws 15-ampere. First, under §1926.403(a), all adapters/plugs must be approved by a Nationally Recognized Testing Laboratory (NRTL). We are not aware of any 20 ampere to 15 ampere adapters approved by a NRTL.

Second, your question raises a problem that goes beyond whether you could obtain an approved adapter. The more fundamental problem is that, in the United States, a tool rated at 15-ampere would overload most circuits equipped with 15-ampere receptacles — so use of such a tool on those circuits would violate §1926.404(b)(2). The only time a 15-ampere tool could be used on a 15-ampere receptacle would be if there was only one receptacle on the circuit, and if 15-ampere was the maximum load that could be imposed by the tool. Since most tools draw above their rated load at start-up, a tool rated at 15-ampere could even overload a circuit with only one 15 ampere receptacle.

If more than one 15 ampere receptacle is on the circuit, the maximum allowable load on the receptacle would be 12 ampere. Branch circuits used on construction sites supplying a single receptacle are rarely used. Since other receptacles on the circuit would be available for use by employees using other tools, the use of a 15-ampere tool would likely overload the circuit. Even a circuit with only two receptacles might be overloaded at some point if a tool of more than 12 ampere were permitted to be used because of the power required to start the tool.

In short, since your drill draws 15-ampere, the OSHA standard would require that it be used on a circuit with a capacity over 15-ampere. In the United States, this would mean using a circuit with a minimum capacity of 20 ampere.

Question 5: Can we use electric power tools rated 15 to 20 ampere on construction sites?

Answer: As explained above, 15 ampere power tools can only be used on circuits rated 20 ampere. As a practical matter, many construction sites will only have 110 volt/15 ampere circuits. As discussed above, because of the power required to start a tool, you usually cannot use a 15 ampere tool on a 15 ampere circuit. Most circuits on construction sites have more than one receptacle, so in that case you would be prohibited from using a 15 ampere tool because there would be an overload when other equipment was used in the other receptacles.

Question 6: Are there over-current tolerances?

Answer: No, the standard does not provide over-current tolerances.

Question 7: Are there States in which the branch circuits on construction sites must be rated 20 ampere (20 Ampere fuse) in order to be able to connect the 20 ampere "Twist-Lock" system?

Answer: We do not know whether there are any such State requirements.

If you need additional information, please contact us by fax at: U.S. Department of Labor, OSHA, Directorate of Construction, Office of Construction Standards and Guidance, fax # 202-693-1689. You can also contact us by mail at the above office, Room N3468, 200 Constitution Avenue, N.W., Washington, D.C. 20210, although there will be a delay in our receiving correspondence by mail.


Russell B. Swanson, Director
Directorate of Construction

[Corrected 6/2/2005]