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.

July 9, 2003



Regional Administrator
Directorate of Construction
Directorate of Construction
SUBJECT: CSHO Use of External GFCI Testers to Enforce 29 CFR 1926.404(b)(1)


We are in receipt of Mr. Gerecke's January 13, 2003, memo asking about the Agency's policy on the use of external GFCI testers by compliance officers. We have paraphrased his question as follows:

Question: What is the Agency's policy on CHSOs using external GFCI testers to determine if an employer has complied with 29 CFR 1926.404(b)(1) by protecting a branch circuit with a GFCI?

29 CFR 1926.404(b)(1)(i) states:



The employer shall use either ground fault circuit interrupters as specified in paragraph (b)(1)(ii) of this section or an assured equipment grounding conductor program as specified in paragraph (b)(1)(iii) of this section to protect employees on construction sites . . . .

Under §1926.404(b)(1)(ii), an employer that elects to use GFCI protection on a branch circuit to provide ground fault protection must meet the requirement that the receptacle outlets:

which are not a part of the permanent wiring of the building or structure and which are in use by employees, shall have approved ground-fault circuit interrupters for personnel protection. . . .

Previous memoranda

In a February 16, 1994, memo from Roy F. Gurnham to all Regional Administrators titled "Testing Ground Fault Circuit Interrupters," the Agency stated:

The purpose of this memorandum is to reiterate the policy for testing ground fault circuit interrupters (GFCIs) used at construction sites.

GFCI testers which are not an integral part of the GFCI shall not be used as a means of determining compliance with §1926.404(b)(1)(ii) because such testers often do not produce accurate results. Only the testing circuit which is manufactured as part of the GFCI shall be used to determine whether or not the device will function as intended. . . .

In an August 13, 1997, memo from Russell B. Swanson to all Regional Administrators, titled "Ground Fault Circuit Interrupter Testers," we stated:

The Cincinnati Technical Center (CTC) of the Directorate of Technical Support has been reviewing available equipment for testing a Ground Fault Circuit Interrupter (GFCI) at construction sites by compliance officers in the field. In February 1994, the Directorate of Compliance Programs issued a directive prohibiting the use of testers that were not an integral part of a GFCI, citing Electrical/Electronic Technical Note 91-1. There were no Nationally Recognized Testing Laboratory (NRTL) listed devices available to test GFCIs when Technical Note 91-1 was written in 1991. This is no longer the case. Several manufacturers have GFCI testers available . . . which are listed to UL 1436, Outlet Circuit Testers and Similar Indicating Devices, that could be used by the compliance officers to test a GFCI.

In light of these new testers, the policy, as stated in the February 16, 1994 memo - "Testing Ground Fault Circuit Interrupters", forbidding the use of external GFCI testers a s a means of determining compliance is revised. The new policy which shall be followed is that if a compliance officer is using an external GFCI tester as a means of determining compliance, the tester must be listed by a NRTL to meet UL 1436 requirements. . . .

Current policy
We understand from your inquiry that there is some confusion about the current agency policy on the use of external GFCI testers. As noted above, employers can elect to meet the ground-fault protection requirement in §1926.404(b)(1)(i) by complying with §1926.404(b)(1)(ii) and protecting the circuit with a GFCI. In investigating whether a violation has occurred, the CSHO should first determine if the branch circuit is equipped with a GFCI device.

If there is no outlet-type GFCI (the type that is installed in the outlet box) or cord-connected GFCI visible, there may be a GFCI installed further up the circuit. A CSHO may use an approved external GFCI tester at the outlet to see if there is a positive reading (indicating that the circuit is GFCI protected). If there is a positive reading, the CSHO may rely on that reading to conclude that the circuit is GFCI protected. This can save time since the CSHO need not trace the circuit back to visually check to see if there is a GCFI further up the circuit.

However, if the CSHO obtains a negative reading (a reading that indicates that the circuit is not GFCI protected), the CSHO must do further investigation to determine whether the circuit is protected. Reliance must not be placed solely on a negative external GFCI tester reading to establish a violation of the standard. This is because there are some circumstances where a negative reading on an external tester can result even though there is a functioning GFCI protecting the circuit.

In the case of a negative external GFCI tester reading, the CSHO should then visually determine if there is a GFCI device installed on the circuit. If further investigation reveals that there is a GFCI device installed on the circuit, then the CSHO should use the built-in tester to help ascertain if the GFCI is malfunctioning. If there is a conflict in the results between the GFCI's built-in tester and the external tester, the CSHO should obtain additional information that will be needed to determining whether the GFCI is functioning properly -- such as testing the voltage of the circuit and determining if the circuit is single- or dual-pole).

This memo supersedes the February 16, 1994, and August 13, 1997, memos referred to above; those previous memos are rescinded.