OK. For those that haven't seen this before, I'm just a-doing the math. Hang in there.
Take standard house wiring. There's three wires that cometh down from the power pole. Take the easy one first: One wire is Neutral; it goes to the breaker box in the house and, incidentally, gets connected to a thick, 6' or so long copper stake that was pounded into the ground when the house was built. (Yes, that's where all the green "ground" wires in a house are connected to.) At the breaker box, neutral and ground are one and the same thing. Everywhere else, not so much.
Next, those other two wires. Each one of those wires is a Hot. Imagine a sine wave. Starts at zero, ramps up to 170V or so, then ramps back down to zero, then ramps down to -170V, then ramps back up to zero volts again, lather, rinse, repeat. That's one hot.
The other hot is doing the opposite. When the first hot is ramping up, the other hot is ramping down. When the first hot peaks at +170, the other hot peaks at -170. And so on. If you think of that picture of a sine wave for the first hot, the sine wave for the other hot is, literally, upside down from the first.
Snag a voltmeter. Read one hot to neutral: you get 120 VAC. Read the other hot to neutral: You
also see 120 VAC. Now for the fun: Read from hot to hot and you'll see 240 VAC, twice the amplitude, because the
difference between the two is 2X either of them to neutral. And that's how the A/C in your house gets 240 VAC to it: The air conditioning (or the wall connector on your Tesla) has two hots, with 240 VAC across them.
If you're math oriented, 120 VAC on the first hot is represented as 120 VAC @ 0 degrees, the other is at 120 VAC @ 180 degrees. Normal houses in the U.S. receive this kind of power which is called, "Two phase".
Fun. Now, three phase. For lots of very good reasons if one is trying to run a high power electric motor, things work a heck of a lot better if there's three or more phases. So, three phase power is pretty common. In fact, if one looks at high tension wires, one will often notice that there's three wires up there, and maybe another wire really high to catch lightning strikes. Yep, the power companies tend to play three phase, all the time.
So, suppose that one has three phases. Commercial buildings get this all the time. They like to light the lights in the building with 120 VAC, just like everybody else uses. So, at the entry to the building, you'll have a neutral (that's also bonded to ground at the building entry), and three phases of 120 VAC to neutral. These will be spread around 360 degrees. So, you'll have one phase, 120 VAC @ 0 degrees, then another phase at 120 @ 120 degrees, and a third phase at 120 @ 240 degrees. Let's call them phases A, B, and C.
Grab the voltmeter. Measure from A to Neutral, B to Neutral, or C to Neutral. You'll get 120 VAC each and every time, and that's the same voltage one can put a light bulb or computer upon, and that's what light bulbs and such get connected to in a commercial building. The Big Honking three-phase Motors that run the assembly line or the air conditioning system will (likely) get 120 three-phase (or bigger), but let's not worry about that.
The interesting question is, "What's the difference in voltage between phase A and phase B, or phase A and phase C, or phase B and phase C?
It's vector math. Let's take Phase A at 0 degrees and plot it on graph paper. 120 V on the X axis.
Next, take Phase B, use a protractor, and make a straight line from the origin to 120 degrees, length 120V. Go from the tip of that line to the +120 on the X axis, and the distance will be 208V - and
that is what the voltmeter will read.
Doing a little math: (120 @ 0) - (120 @ 120) = 120 + j0 - (-60 + j103) = 180 - j103 = sqrt(180*180 + 103*103) @ 29.77 = 207.39 VAC @ 29.77 degrees.
The magnitudes of the voltages between phases will always be 207 VAC; the angles will be silly buggers that the voltmeter can't measure anyway.
The Tesla won't have a problem working off of 208 VAC on the two "hots" out of three, except that with 208 VAC and 48A the power into the car (the car is
current limited) is 9.98 kW. At home, where one would have 240 VAC at 48A, the power input would be a bit higher at 11.52 kW. (Remember: P = V * I)
Now, just pulled up the Tesla Wall Connector installation book. Interestingly, it says that the Gen 2/Gen 3 accepts
single phase power. Literally, it says, "Nominal 200-240 V AC single-phase". Which simply means that the voltage measured across the two, high-power wires going into this thing has to be between 200 VAC and 240 VAC. (Note: We're
not talking about neutral, here.) Further on, we got the following:
So, note the terminology. "L1, L2/N, and Ground". That's interesting: So, suppose we got the three phase power in the building. Grab two of the phases, A and B (or A and C or B and C), attach to L1 and L2 and one is off to the races with 208 VAC.
BUT if one has, say, some kind of power system where there's 230 VAC to neutral, then they sure seem to imply that neutral had very much better be on the L2 connector, not the L1 connector.
Now, looking at
@J.Kreed's commissioning post, that sure looks like a (slightly reduced in amplitude) two phases of a 120 VAC three-phase system. If one does the math (117.3 @ 0 degrees; 114.1 @ 120 degrees) then one gets a magnitude of 200.1 VAC, which is spot on. Hm. It
is a trifle unbalanced, though: One would expect equal voltages. But not by a lot.
Thing is, the car will look for major unbalances and such with respect to ground and refuse to charge under those circumstances. Somehow, a difference of a little over three volts doesn't look like
that much.
However, I have a different idea. It's well-known that if, as a Tesla starts charging, if the
input voltage drops dramatically, the Tesla will very much
stop charging, pretty much on the spot. This is a safety feature, as in, "We don't like to see houses/buildings catching on fire." Say one has a loose connection. On a good day, said loose connection might make incidental contact with the metal on both sides and have Low Resistance. Run lots of amps through it, nothing much happens. Might get a little warm.
On a bad day said incidental connection might have one or two ohms of resistance. Run 48A through an ohm, P = I * I * R = 48*48 * 1 = 2.3 kW at that resistive spot which is smallish in area and Flames R Us. The voltage will drop by V = I * R = 48 * 1 48V, so it'd go from 208 VAC down to 160 VAC.
So, you probably don't have an ohm of resistance in there. But you
might have a hundred milliohms or something, your car sees the drop, goes, "Oh noes!" and stops charging.
All it takes is for on the several wire connections between the TWC, the breaker box, and the power transformer, is one not-as-tight-as-it-should-be screw.
No offense to anybody, but have the electrician come on back with his mini torque wrench and make sure everything is torqued down properly. As a first guess.
And, if I had to guess: Start with that slightly-low-voltage L2 phase.