Wiring the Inverter AC Ground 1. Combine the ground (green) wire from the main panel’s ground buss bar and the ground (green) wire from the sub-panel’s ground buss bar (or the ground connection on the outlets, if using the output breaker versions). After these grounds are combined, use field wiring leads to connect them to the inverter’s AC GROUND (green) wire.
So be sure you can read continuity between the ground buss bar in the main panel and the ground terminal on the Magnum. The ground path should remain constant throughout the entire AC circuitry. The hot and neutral conductors will be switched through the automatic transfer switch, but the ground conductor should not be switched. It could be a ground wire came loose some where in the system between the inverter and the breaker box(es). But measuring with a VOM should determine if and where the open exists. Since an open ground circuit is potentially dangerous, it may behoove you to contact a certified RV technician to perform further testing and measuring just to be safe.