Screw conveyor on the batching line, 3hp 460VAC, line fed through a contactor from the PLC. It jammed on a lump Tuesday, stalled, and by the time anyone noticed the motor was smoking. Nameplate FLA is 4.8 A.
Panel was built last year by an outside builder. Breaker, contactor, motor, and that's the lot. I've been through it twice and I still can't find an overload block anywhere in there. Bench checked the breaker and it's fine, 15 A, and the motor's away at the rewind shop.
My guess is the motor was undersized for the screw and the breaker should have tripped long before it cooked. Is a 15 A breaker enough protection for a 4.8 A motor, or do I want a smaller one in there? Could someone explain what's meant to catch a stall like that?
Breaker is short circuit protection. It's sized for the starting inrush, 15 A on a 4.8 A motor is normal. A stalled 3 HP pulls maybe 30 A. On the breaker's thermal curve 30 A takes a minute or more to trip. The winding doesn't have a minute.
The overload is a separate device. Is there anything at all between the contactor and the motor terminals? Photo of the contactor with the cover off.