Sub-Panel breakers trip on load
I have a sub-panel circuit box in the garage with four breakers. My 20 amp breaker trips immediately when I engage my larger power tools such as circular saw (12 amps), table saw or other similar sized tools. Smaller tools like my drill, sander, fans, lights are okay. The 20 amp breaker should easily handle the larger tools. Suspecting a bad breaker, as a test I tried the other three circuits and they also trip when engaging my larger power tools. Now I am suspecting a panel issue. The sub panel has a 30 amp main on it and is fed by my main house panel. The house panel has two 20 amp circuits (separate phases, linked together) that feed the garage sub panel.
I just bought the home and I am not familiar with the code for feeding a sub panel. Does this sound like a proper setup? Any ideas why this is occurring? Also, as the sub panel is being fed by two separate phases, I presume I can have 220 circuits up to (40,30 amps?) off of that panel?