[Foldbak]

It's not the inverter. It sounds like you have a shower power issue. Check voltage at the pedestal. The inverter has to be on to provide power to the inverted plugs. It has a built in transfer switch that passes shore power to the plugs. If you turn it off those plugs won't work. The microwave isn't on the inverter power. It's on shore power or gen power. Since the microwave works on gen power it's a sure sign the shore power has an issue. If you have a built in gen then you have a transfer switch that switches between shower and gen power.