Is your 120v outlet connected to another circuit or outlet somewhere in your house?
Because if it does, your Voltmeter will also read the lights, fans, etc's power consumption if those were connected to the outlet where your Antminer was previously plugged.
I checked the "utility" in the antminer configuration page when it was plugged into 240 but it still showed 7.9 amps. That cant be right.
I wasnt using a volt meter i was using a watt meter so it only reads whatever you plug into it. But I cant use this watt meter on the 240 because the prongs are different on 240 and 120.