I've got a DC powered ham radio in a spare bedroom converted to an office, with a coax feedline running up to an antenna up in my attic near the ridge. About six months ago, I upgraded my feedline to a low-loss LMR400, and only since then transmitting often trips one of two AFCIs.
The office with the radio and a nearby bathroom are powered by an MWBC. In the panel, the MWBC is fed by two Eaton BR AFCIs next to each other that each feed a phase of the MWBC properly(from each phase of the main). Both have their neutral pigtails to the neutral bar, but the MWBC shared neutral only goes to the breaker for the bathroom. I've checked the GFCI and downstream receptacle in the bathroom with a plug tester, and also verified that the office is not protected by GFCI that is sometimes built into AFCIs. Here's a diagram of the situation, ground not shown:
When I transmit for more than a second or two, one of two Eaton BR AFCIs will trip with blinker code 6 (self-test failure), once that occurs the other won't trip. It seems random which AFCI trips. If it's the breaker for the office, the radio obviously stops getting power. If it's the breaker for the bathroom, radio continues to work without tripping its AFCI.
Things I've tried that did not help:
- Replacing the AFCI breakers with two news ones from the supply shop.
- Replacing the AFCI breakers under warranty with Eaton - the old model the house came with had a known succeptibility to radio frequency interference. The replacements ended up being the same ones from the supply shop.
- Powering radio power supply through an isolation transformer.
- Powering radio power supply from extension cord from another circuit on first floor.
- Powering radio with two different AC->DC power supplies.
- Adding ferrite beads to outside of coaxial feedline to reduce stray RF coming off the feedline - still trips an AFCI.
- Doing the above with everything on those circuits but the radio disconnected.
Things that I've tried that did help:
- Unplugging antenna coax and replacing with a dummy load. Since the breakers do not trip when transmitting, I believe the nuisance trips are caused by radio frequency interference(RFI) with the house wiring.
My locality does not yet require arc-fault protection, but they're a good idea so I'd like to keep arc-fault protection for both phases if there's a way to do so without nuisance tripping when using my radio.
I know that when powering an MWBC with two breakers, they need to be handle-tied so the whole MWBC shuts off at once, so even outside of the radio tripping, I should be doing something about that anyway.
For Eaton BR AFCIs, is the neutral lead only used to power the electronics inside the breaker, or is it actually used for fault sensing like it is on a GFCI? If so, is it expected that installing a 2-phase AFCI breaker will fix my nuisance tripping on transmit? Or should I go to a 2-phase thermal breaker? This is the current state after replacing the originals with the recommended ones from Eaton support: