Pool pump and circuit keep tripping breaker

[Jesse Ferrara]

first year experiencing this problem, pool pump will run for about 3 hours at most than will trip the afci gfci 20a breaker. If I reset breaker it trips instantly.  If I unplug the pool pump and reset breaker it still trips under zero load.  The feed is a 12g ran underground presumably in conduit to a manual Westinghouse disconnect and connects to the pump with an older style 3 prong twist lock connector. If I leave it over night off ,the next day it will work again for up to 3 hours when I turn it on.  What the hell is going on??  Being a lineman by trade I understand electric but residential isn't something I'm very versed in. Any help would be greatly appreciated. Thanks in advance

[Steven Epps]

@Jesse Ferrara how long is the wire run? Sounds like a thermal issue.

One of three things IMO: If the motor is older the bearings could be going out on the impeller. Inlet could also be clogged, increasing draw and thermal load over time. Thermal breaker could be going bad as well. Replacing the thermal breaker: http://www.inyopools.com/HowTo... The thermal breaker is most likely whats causing you to trip. Whether or not that's because its going bad or something else is going to be up to troubleshooting.

Doesn't sound like a start cap since it is starting up without an issue after it cools off. Do you have a IR thermometer? I'd check the wire temp at both ends and the motor before starting and an hour or so after running.