This the main breaker on the AC panel, it supplies all of the other breakers. The thing is, it doesn't trip when you plug IN the shore power, it rips when you unplug the shore power. Once reset it is fine until the shore power is unplugged again. I have tested the sub-breakers already and discovered just how many lights and heaters can be plugged into the outlets. Most interesting is that neither the breaker supplying the power to my cord or the main breaker on the boat panel tripped, just the breaker supplying the outlets. I assumed that it was a 15 amp unit although it does not show the number.