Cottonwood
Roadster#433, Model S#S37
I'm VIN 37 with an "A" battery. I can confirm that with a TT-30 to 14-50 adapter (the correct Tesla variety), my charge rate at 120 Volts is limited to 20 Amps.
I can also confirm that if the neutral and line are not connected the way the UMC expects 120 Volts, then the UMC complains with 4 red light flashes and won't charge. 4 flashes indicates "Ground Lost" so I guess the UMC expects ground to be close in Voltage to the assumed Neutral for 120 Volts. I have a home made multi-adapter extension cord that swapped L1 and L2 by accident. I corrected the swap and the UMC charged my MS at 120 Volts/20 Amps just fine with the adapter feeding the extension cord, feeding the UMC, feeding the MS...
I can also confirm that if the neutral and line are not connected the way the UMC expects 120 Volts, then the UMC complains with 4 red light flashes and won't charge. 4 flashes indicates "Ground Lost" so I guess the UMC expects ground to be close in Voltage to the assumed Neutral for 120 Volts. I have a home made multi-adapter extension cord that swapped L1 and L2 by accident. I corrected the swap and the UMC charged my MS at 120 Volts/20 Amps just fine with the adapter feeding the extension cord, feeding the UMC, feeding the MS...