I had my electrician install a nema 14-50 plug to use with the included adapter that came with the model 3. He used a 50 amp breaker and 6/3 wire. After the install, he used a voltage meter on the plug and both sides were reading 120V, so 240V total. It clearly has enough power. However, when I plug in the charger, nothing happens. No lights come on at all. At first I thought it was a problem with the charger, so I tried plugging it into the 14-50 plug in my kitchen that the stove uses. It powered on just fine. The kitchen plug uses a 40 amp breaker.
I called Tesla and they don't know what the problem is. What could be going wrong?
If you are comfortable with electricity and have a multimeter I would check the following:
From each "hot" to neutral should read roughly 120v. From each "hot" to ground should be roughly 120v. From hot to hot should be roughly 240v.
As others have mentioned, if both sides were hooked to the same "leg" of the panel there would be no "potential" between them, but that would be pretty hard to screw up since the breakers themselves are dual pole and physically only fit in the panel across two phase legs.
Interesting that your UMC comes on when plugged into the kitchen plug. That makes it seem like it is not an issue with the UMC.
Note that the UMC does test for you having a solid ground connection so if the electrician failed to connect up the ground properly that could explain why you have good voltage hot to neutral but yet the UMC does not work. (btw, the UMC totally ignores the neutral, so it could be totally disconnected and the UMC would not care)
Your kitchen should not have a 14-50 using a 40a breaker. But we’ll leave that alone.
Actually, this is a common misconception but it is completely legit to have a NEMA 14-50 on a 40 amp circuit as long as the range/oven plugged into it does not violate the 40 amp ampacity rating of the circuit (after applying the allowed demand factor which actually reduces your circuit ampacity requirements). I am looking at 2017 NFPA 70 / NEC Article 210.21 - Outlet devices.
My reading of the NEC actually would allow you to use a 40 amp circuit on a NEMA 14-50 receptacle for your UMC since the UMC Gen 2 only has a nameplate rating of 32 amps, so a 40 amp circuit actually meets the 1.25 continuous load multiplier requirement.
Btw, have you tried the UMC with the plain old NEMA 5-15 adapter that comes with it as well just as another data point? (if it works on your Range plug though that is probably the best test of the UMC since it even uses the same adapter)