Ground fault

[HappyFace]

Working on a older house built in the 1970s there is an issue with three circuits on the first there is a ground fault and on the circuit in the origin is unknown and we really haven't had chance to troubleshoot to locate it yet and is not really the concern because it was found immediately . The other two circuits or of a concern both circuits were tested with a standard breaker and there was no issues lights and outlets were working properly but after the circuits were placed in a AF CI breaker the circuits tripped and they now have a permanent ground fault and any ideas?

 

[augie47]

If the circuit works on a standard breaker but trips on a G/F breaker there's a good chance the neutrals from two different circuits are tied together. Often happens where there are two circuits in one box.

 

[ptonsparky]

AFCIs do not tolerate being misswired or attached to wiring with faults. Standard breakers will not detect the shared neutrals or possible high resistance ground faults. You can start with a typical continuity test but you may have to upgrade to a Megaohm meter.