zman-az wrote:
I too thought inverter was running everything with low batteries but the OP said it was not on.
As suggested, what is the voltage at the pedestal when you run the microwave. If it drops then the problem is not the RV. I would check all electrical connections on the 50 amp circuit. A loose screw can cause these issues. Check the circuit breaker on the house/pedestal. Turn it off then put in a large flat blade screwdriver and turn the screw on the CB, if its loose snug it down. Also check connections on the transfer switch as well as the circuit panel in the RV. If any of the connections are loose it can create this issue. Make sure power is off and you have a insulated screwdriver so you don't electrocute yourself.
The Inverter may be OFF now because the Battery voltage has dropped too low and the Inverter has kicked off. Since the OP does not understand electricity, they may have a problem with HOW the Inverter functions and if it was ON or OFF. If it was on standby(very common for experienced and novices), then it was NOT ON, but waiting for a drop out of Shore Power and when the shore supply TO the Inverter was lost the Inverter came on and slowly depleted the batteries. I have a unit (2011 Phaeton) in the shop right now that had 1 leg of the 50 amp dead because of a bad transfer relay for that leg, and the result was--NO 120 to the Inverter and no charging, but the Inverter was ON and supplied power to the Kitchen and M/W(until the batteries went dead). But the other leg was HOT and the AC units ran and the customer could not figure out why. Doug