C.B. Amp Ratings
are found on a sticker affixed to the Circuit Breaker. Make sure the main DC switch is off and the Shore Power Cord is unplugged before opening the panel and digging around. Remember the amperage of the C.B. should be lower than the rating of the wire it's designed to protect. You should also be aware of the potential current draw of the device that it is wired to to make sure that it is properly sized.
