ARRL Helps Manufacturer to Resolve Arc Fault Circuit Interrupter RFI Problems
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.
Gruber contacted Eaton, and two of the manufacturer’s engineers visited ARRL Headquarter in August. “Eaton was extremely cooperative and eager to resolve this,” Gruber recounted. “They spent the day with us, going over our test methods and took some of the problematic breakers back with them, eventually developing a modified version.
“We have just finished testing the new version of the breaker, and it did not trip during W1AW transmissions and in other tests,” Gruber reported. He said the new breaker is still in the queue for UL approval.
Eaton Engineering Director Andy Foerster said arc fault detection is challenging, in part because so many common household devices — such as vacuum cleaners and power tools that use motors with brushes — create arcing. In information provided to ARRL Eaton engineer Lanson Relyea said that because AFCIs rely on HF emission detection to verify arcing, “any signal that conducts or radiates a signal within the detection band of the AFCI can cause interference and cause the device to trip without the presence of a true arcing condition.”
Foerster explained that all arc fault devices must meet the requirements of UL standard 1699. “This standard requires a very extensive set of tests to confirm that the device will detect an arc, that it will not nuisance trip in the presence of a set of common loading conditions, and that it will resist a variety of environmental noise sources,” Foerster told ARRL. “Among this last set of noise sources is radiated electromagnetic field immunity and immunity to conducted disturbances.”
Foerster said AFCIs use “some pretty sophisticated digital signal processing technology” to distinguish various types of arcs. “They continue to get better, but they are not perfect,” he added. “And the governing philosophy is that they should err on the side of tripping.” According to Foerster and National Fire Protection Association (NFPA) statistics, the use of AFCIs appears to have contributed to an overall decrease in house fires from electrical causes. When the National Electrical Code (NEC) begins to specify AFCI receptacles next year, Foerster assured, these will include “the immunity to ham radio RFI that we have developed with the testing assistance of the ARRL.”
Eaton and ARRL agreed that when the manufacturer comes out with any new models of breakers, it will ask the League to test them at W1AW. “It’s a win-win situation,” Gruber said. Eaton also has agreed to work with anyone having a problem with RF tripping its AFCIs. Eaton says that AFCI manufacturers “are aware of this compatibility issue and are actively working to correct this in future products.”
Eaton’s Relyea said that hams experiencing unwanted tripping problems with their or their neighbors’ AFCIs should contact the manufacturer as the first step in rectifying the compatibility issue. In the case of Eaton breakers, contact Bob Handick (412-893-3746) or Joe Fello (412-893-3745).