How long does it take to charge up the car, like 3 hours? In looking at your picture, I guess the two prongs are hot and then the third is the ground. Does it matter which is which in the hot wires? I'm guessing not..
Edit: I just looked in the basement I have left over Romax 10-3 cable I ran for the electric oven some years back. Its got red, white, black, and a copper ground in it. With 240v if I remember correctly there are two hots (120v each) and one neutral and the copper is ground. How did you connect the 3 prong cable you made for the 120v charger? If I make one I just want to make sure I do it right no mistakes.
About 2-2.5hr, based on FORScan Lite the JuiceBox 40A charges about 19% faster than this. I have found the C-Max only pulls 14A from a full L2 vs 12A from this setup. Not too shabby really.
IIRC it doesn't matter, and the reason is that both hots have a path to ground via the neutral-ground link back at the breaker panel (which the hots can get to via the transformer center-tap at your transformer outside, or Wye-neutral for 3 phase commercial building power). The reason that matters is for GFCI. I think the only folks who would see this scenario fault are those using a cheap-o generator without ground-neutral connection built in. The main thing I guess is the EVSE has to check first if the ground is wired correctly, and my guess is that it checks the Hot->Ground voltage potential (i.e. from the 5-15's "hot" blade, the smaller of the two, to GND, which in this case would reveal 120V). If it's 0V, then it would throw a ground wiring error indicator I guess.
The adapter's cable itself is service cord from Lowes, 12-gauge SOOW 3-conductor, i.e. a black, white and green (ground). Green goes between the 5-15 ground and 6-15 ground, black & white connect to the hots of the 6-15 without any regard for order.
Your romex 10-3 cable (actually 4-conductor since the ground isn't counted for that particular nomenclature) has one more conductor than you'd need here, you only need the two hots to go to the 5-15's hot & neutral and the ground to go to the ground.
Edited by spirilis, 11 February 2018 - 07:23 PM.