New circuit added, now I’m getting nuisance trips with light loads

[DarkHector]

I’m kinda stuck wwith this and it’s getting frustrating. We added a new circuit recently and everything looked fine at first, but now the breaker trips even when the load is pretty light. It feels random enough that it’s hard to trust. One example: I had just a couple basic things plugged in, nothing heavy, and it still tripped after a short while. Reset it, it ran fine, then later it tripped again when someone turned on a small appliance that normally wouldn’t be a big deal. No obvious burnt smell, no hot outlet, nothing like that. Just trips. For the pros here, what’s your first suspect in real life when this happens? Shared neutral, a loose connection somewhere, arc fault sensitivity, or something else you’d check before tearing everything apart?

 

[BarryEnergy]

If that new breaker is AFCI, I’d put that high on the list. AFCI can be picky, especially if there’s a shared neutral, a bootleg neutral/ground situation, or something wired wrong in a box. First real-life check is usually wiring and terminations, then confirm the breaker type and what’s on that circuit.

 

[PGB1]

Hi DarkHector,
BarryEnergy made a very good point about AFCI.

You mentioned shared netural. Did you run 2 new circuits with a shared neutral?

Some AFCI have trouble with shared neutral & separate breakers. If I remember correctly, Eaton BR is one brand that has problems. If you have a shared neutral, most manufacturers want a two-pole AFCI for those circuits.

Note, too, that combination arc fault-ground fault circuit breakers cause lots of problems with shared neutrals. Using 14-2-2 or 12-2-2 NM cable would be the best plan for two AFCI-GFCI circuits scenario. (One cable run for two circuits)

Unfortunately, AFCI problems can be tedious to troubleshoot. Since you already know that the connections are done properly, it would be wise to remove one item at a time in order to find out who is the troublemaker.

Example:
Recently, I was called for AFCI tripping randomly. What I found was a wall sconce that had a partially separated conductor within the fixture itself. Even with the lamp off, the AFCI would occasionally trip when anything else was connected to the circuit. Once the lamp was removed from the circuit, all was good. (Taking the fixture apart confirmed the partial separation in the conductor.)


Keep in mind that some devices trip AFCI even when working properly. We had a bread toaster that would trip AFCI. The little arc when the lever was pushed down was too much for the AFCI, so it tripped. Things with contactors and relays also sometimes can trip AFCI- even though they are working properly. Items with no switch or a switch turned on when plugged in can also trip AFCI due to the load. Items with heating elements are prime candidates.


Another strong possibility is simply a defective circuit breaker (AFCI or non-AFCI). Even a brand new circuit breaker can randomly trip with a light load or even with no load if it is defective, Do you have another circuit breaker to swap in for a check out?

Some brands have a higher defect count than others. Square D Homeline is an example of a brand with high defect count.

Hope This Helps!
Paul

 

[Carrot_]

have you checked the breaker face for a small LED. most modern AFCIs have diagnostic blink codes.
when it trips, don't just reset it! look for a pattern (like 3 blinks = arc fault, 5 blinks = ground fault)

some even have the Time Saver Diagnostics where you hold the test button while flipping it on to see why it last tripped. this saves you from guessing if it’s a loose wire or a picky appliance