The general rule ofthumb is that circuit breaker size should be rated 125% of the ampacity of circuit requirements. For the calculation example, use the 6000XP nameplate sticker listed above. The max ACinput is rated at 45A. United Industries notes that in factories, poor breaker selection and. Determine what size inverter-to-battery cables and DC breaker (or fuse) you should use with an off-grid inverter to install and operate it safely. In contrast, an undersized or oversized. Common NEC standard breaker sizes are 10, 15, 20, 25, 30, 35, 40, 45, 50, and 60A. A 16A continuous load screens to a 20A review point, and 12 AWG copper still stays capped at 20A on a general branch circuit.