There were many complaints that the HGT6120 would not function correctly on an AFCI Circuit Breaker, causing the breaker to trip as soon as you plugged our tester in. AFCI translates to Arc-Fault-Circuit-Interrupt and on many new models comes equipped with a self-test. We went ahead and started testing to see what the issue was while using the HGT6120 and all of our other GFCI circuit testers on AFCI circuits. During testing we used many different AFCI circuit breakers from multiple vendors. We of course did not find any issues or have any problems using our circuit testers on any of the new AFCI circuit breakers.
There is one other theory as to why this is happening on AFCI circuit breakers. It could be that the circuit breakers being tested are older and more prone to tripping. Circuit breakers are like most switches and over time they wear down. If this is the case and they aren’t functioning properly, they may need to be inspected and replaced. In any case, a licensed electrician should be involved to determine the root cause of the problem.