Recently, there have been a number of questions from the field about the response of arc fault circuit interrupter (AFCI) circuit breakers to commercially available AFCI indicators. AFCI indicators operate by producing a waveform similar to an arc fault. However, because they cannot produce an actual arc fault, an AFCI indicator may not trip every available AFCI.

Therefore, if an AFCI indicator plugged into a receptacle protected by an AFCI does not trip the AFCI, it does not mean that the AFCI protecting the circuit is defective and needs to be replaced. When this situation occurs, you should push the "Test" button provided as an integral part of the AFCI itself. If the integral test button does not trip the AFCI circuit breaker, it should be replaced.

To notify users of this product limitation, Underwriters Laboratories Inc. requires AFCI indicators to be marked or be provided with instruction manuals that state the following or equivalent:

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CAUTION: AFCIs recognize characteristics unique to arcing, and AFCI indicators produce characteristics that mimic some forms of arcing. Because of this the indicator may give a false indication that the AFCI is not functioning properly. If this occurs, recheck the operation of the AFCI using the test and reset buttons. The AFCI button test function will demonstrate proper operation.

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For more information on AFCI indicators, contact Steve Brown in Melville, N.Y., by phone at +1-631-271-6200, ext. 22420; or by e-mail at Steven.A.Brown@us.ul.com. If you find a defective AFCI, please alert the product's manufacturer and UL through UL's AHJ Product Report Form available online at https://www.ul.com/regulators/ahjprod.cfm.

Smells like the makings of a lawsuit down the road, when a fire starts on an AFCI "protected" circuit....