Minor but important nitpick: Circuit breakers are designed to protect the wire going to whatever needs electricity (light bulb, pump, expensive box, other widget). Wires are sized to deliver enough power to meet the demand; CBs are sized based on the wire size. If that wire shorts to ground then the CB is supposed to pop before that starts an electrical fire. But CBs aren't guaranteed to protect what's in side the box from an internal malfunction.CBs are designed to protect expensive electronic equipment from being zapped from too much current.
(Think about it- 5 amps going the wrong way inside any radio will let all the smoke out of the box... and with no smoke left, the box won't work anymore.)