The ARRL Lab has worked with a manufacturer of arc fault circuit interrupter (AFCI) breakers to resolve complaints that Amateur Radio RF was causing certain breaker models to trip unnecessarily. Like the more common ground fault circuit interrupter (GFCI), the AFCI is a safety device. Primarily designed to detect problems that could result in a fire, AFCIs detect potentially hazardous arc faults that result from often unseen damage or poor connections in wiring and in extension cords and cord sets.
“Several months ago we started receiving reports from amateurs that when they transmitted, their AFCI breakers were tripping, ” said Mike Gruber, W1MG, the ARRL Lab’s EMC specialist. He notes that the issue has been a topic of online ham radio discussions as well as on homeowner sites; it seems that stray RF is not the only thing that can cause a “nuisance trip” of an AFCI. Gruber pointed out that the National Electrical Code (NEC) already requires AFCIs in some household circuits, but not all US jurisdictions have adopted the requirement.
Gruber said that as AFCIs became more common in new construction in the US, reports started coming in that AFCIs in the vicinity — not just in the radio amateur’s home — would trip in the presence of RF from an Amateur Radio transmitter. While each manufacturer’s design is proprietary, most AFCIs detect arcs by monitoring the shape of the alternating current waveform, changes in current levels, voltage irregularities, and the presence of high frequency emissions or “noise.” The ARRL Lab dug into the problem.
“Last summer we built a test fixture in which we could test any type of circuit breaker, ” Gruber said. It involved using W1AW as an RF source. Gruber says he bought one of “every AFCI that I could get my hands on, ” but when the Lab began testing them during W1AW transmissions, none of the devices tripped.
A ham in New Mexico who had reported AFCI problems sent some of his breakers to the ARRL Lab, “and those tripped when we tested them, ” Gruber said. The problematic breakers were certain models made by Eaton Corporation. “We already had an Eaton breaker, an older model, but it did not trip, ” he noted, adding that the breaker had a yellow button. The newer model, which had a white button, did trip in the presence of RF, however, even at power levels down to about 50 W on 17 meters.