I'm running a sub panel to my shop. It is a double pole 50 amp breaker at the house. Does my sub panel in the shop have to be 50 amps or less or can I install say a 70-100 amp sub panel and just not max it out?
The sub-panel itself you are installing in your shop would have to be rated for at least the ampereage that it's being protected by....in the scenario you describe, it would have to be rated at least 50 amps. It can be rated for more, but not less. Any breaker used in the sub-panel that is larger in amperage then the feeder overcurrent protection (the 50 A in the house) is going to act as a disconnect. Any breaker less in size will act as an overcurrent device.