quote:I rechecked the wiring and all seems right.
You are using a double-pole breaker, right? It should have two toggles that are joined together so if one phase trips, both breakers trip in unison.
You do NOT want a 'twin' breaker, that is just two smaller case single pole breakers in a common housing - they are made to save space.
To check, remove the breaker. The two metal tangs that engage the buss bars should NOT be mating to the same bus bar. If they are, you have a twin, not a 2-pole.
Third image in the photo shows the tangs on a two pole.
I imagine this is not your problem, the compressor would surely run very slow if at all, but most folks don't deal with 208/220 breakers very often.
3HP on a 20 amp circuit should be fine.
Larry
