Aside from what others have posted, keep an eye on that 120v outlet and make sure that it doesn't overheat. Sounds like you'll be running it at 100% rated capacity for over 24 hours straight. Personally, to be safe, I would replace the receptacle with a commercial one and make sure that the wires connect by wrapping around the screw terminals and not the spring-loaded backstab connections (which tend to get loose over time and could overheat when charging for many hours at a time)...Enjoy your new car!!!.
Yeah, let's get into safety margins, fusing, and wires.
So, the United Laboratories, of "UL" fame, and the National Electric Code, written by electricians, engineers, and PhD's everywhere, standing in the smoking ruins of houses where Things Didn't Work Out Well, have put together a bunch of standards. Which, if followed correctly, means that, in general, a house
won't burn down due to properly installed wiring.
And when I say, "smoking ruins", I'm not kidding. Follow me here: All wires have
resistance, measured in ohms. Ohm's law says the voltage down the length of a wire is equal to the resistance of the times the current flowing through said wire. That is, V = I * R, where I is current and R is resistance.
Now, the
power dissipated (as in, heating up the wire, just like the heaters in an electric stove) is the voltage across the length of wire times the current through that wire. Or, P = I * V. But! V = I * R, so, doing a little substituting, we get P = I*I*R, where R is the resistance of said length of wire, I^2 is the square of the current flowing through the wire, and P is the power being dissipated.
You've probably noticed this heating effect with the household vacuum cleaner. Run it for a while, then touch the cord. It
will be warm. But not hot enough to scorch things, vacuum cleaner manufacturers aren't idiots.
So, the bigger the gauge of wire, the lower the resistance of a particular length of said wire. The smaller the gauge of wire, the bigger.
The deal is, it's perfectly possible to run enough current through a wire to get it to the point where said wire
melts. If said wire is inside cable, mounted inside a wall, before the wire melts, it'll catch the wall on fire. (This is done for demo purposes in EE201 classes everywhere.)
So, the NEC and the people who wrote it are all over this, "let's heat up the world until it catches on fire!" bit. Remember that copper (or any metallic conductor) costs $$, so there's this push to make the wire as thin as possible. I use 30 GA wire (that's the tiny stuff) when building electronics widgetry where the current is down in the milliamps or so. When one is playing with, say, 1000A, then one starts playing with Great Big Honking Bus Bars.
Now, say that one is playing with a standard 15A circuit. The breaker, whose purpose is to Save The Day when there's a short out there, is rated so that at exactly 15A it's got a roughly 50-50 chance of opening up. The Wire that's runs from the breaker to the load is designed so that, if one has a 15A load for some reason, said wire
won't get hot enough to burn the house. And the socket, at the end of the run, is designed to handle 15A, so that if one plugs in a vacuum cleaner or coffee pot, the socket won't melt and burst into flames.
But there's this thing: Say that one plugs in a vacuum cleaner and turns it on. Or a lightbulb. In the first instants of being turned on, while the motor in the vacuum cleaner is just beginning to turn or the light bulb is just warming up, one will get a
lot more current than that 15A circuit is rated for. But that's OK: Within a second or less, the current drops to below 15A and everybody's happy, and the breakers are designed to prevent nuisance trips. (Breakers designed to be hooked up to big honking motors are sometimes labeled, "slow blow", with this characteristic in mind.) Breakers are designed so that, if there's a short (or partial short) out there, they
will pop open on an 1.5X or 2X overcurrent or some such
before the wires in the wall get hot enough to burn the place down, slow blow or no slow blow.
But, the NEC states, and I'm with them on this: If one has a long duration, high-current load, then the maximum current on that circuit
shall be 80% of the circuit rating. Period.
No nuisance trips from Ye Breaker. No wearing out the breaker early, either: A busted breaker might
not trip when one needs it in an emergency. And all the tables about wire size and heating, which is for long-term loads, aren't violated.
Tesla isn't stupid, nor do they want their car buyers to burn their houses down. Got a
NEMA5-15 socket adapter (standard 15A 120 VAC plug) on your mobile connector? Maximum current the car will draw will be 15A * 80% = 12A, for 1440 W. If one has a NEMA5-20 socket (that's the one with a right-angle blade, see the link to the chart) and the adapter, one can draw 20A * 80% = 16A, for 1,920W, and get a couple more miles of charge per hour. Note that, in this case, both the
wire in the wall and the
breaker in the box have to be rated for that 20A.
Take that wall connector in my garage that I mentioned in a previous post. I said that, with it, I can charge the car at 240 VAC and 48A. Think about that 48A. No, there's not a 48A breaker in the breaker panel: There's a 60A (48A/80%) breaker and copper wiring that's also good for 60A, hardwired into the wall connector.
Which brings up a snivvy, often mumbled about in the forum. So, as it happens, there are people out there who buy electric cooking ranges that run at 32A and 240 VAC. So, if one is using such a thing, one would follow the 80% rule and use a 40A socket, wire rated for 40A, and a 40A breaker. Fine.
But check out that link to "NEMA", up above. There are 15A sockets; 20A sockets; 30A sockets; and 50A sockets, but, sure and begorrah, there aren't any 50A sockets. So the NEC says, in the specialized case of Ye Electric Range, that one can use a NEMA15-50 socket for that 40A circuit, backed up by wire that's good for 40A and a breaker that's labelled 40A. Because 40A wire is
cheaper than 50A wire. And, so long as one does all that, one is safe.
Until some cock-a-mamie Tesla guy with a NEMA15-50 adapter on the mobile connector plugs into it, because of course, by now, any labels that were placed on this install are long gone. And the person doing the plugging wouldn't necessarily have a clue, anyway. So, for at least that reason, the Tesla Mobile Connector with a NEMA15-50 adapter on it will only draw 32A. The Tesla guys can't tell if it's a true 50A circuit or a 40A circuit, so, in the interests of Not Burning Down The House, the current is limited to 32A.
Now, it's possible to find a Tesla Wall Connector that can be connected to a NEMA15-50. But, in that case, the Wall Connector has settings where one
tells the Wall Connector the amperage of the circuit to which it's connected. And the car will, when informed by the CPU in the Wall Connector what the ampacity of the circuit looks like, will follow the 80% rule. Only a suicidal person would configure the Wall Connector for a higher current than what the circuit it's hooked up to is good for.
Finally: Turns out that in many locales. if one has a socket in a garage, one is supposed to have a GFCI socket or breaker on that socket. For 240VAC, the costs of said GFCI and socket (a good socket, one that can last) are equal to or really close to the cost of a Tesla Wall Connector. At which point, one asks oneself, "Why make life more complicated and unsafe? If I'm going to add a high-power charging circuit anyway, why not spend the relatively small amount of money for the heavier wire, throw in the Tesla Wall Connector, and be done?"
And a lot of people do that. On the other hand, if the garage
already has a 240 VAC socket for some reason, or there's a clothes drier outlet in the garage, or the garage is detached and there's a sub-panel in the garage, but it certainly isn't good for an additional 60A, it makes sense to cheap out, go with the flow, and maybe buy a spare TMC cable to leave permanently hooked in.
And there's the issue about Just How Big Is That Breaker Panel, Anyway? My house is relatively new construction, had plenty of spare slots, and the breaker panel was good for 200A, so adding a 60A duplex breaker wasn't a problem. Not to mention that the breaker panel was
in the garage. But there are 100A service breaker panels out there, I've actually seen 60A service panels, and so on. FWIW, a lot of states (New Jersey, for one, but there's others) will subsidize either the installation of a car wall connector, a bigger breaker panel, or an increased current drop from the power pole, or some subset of those, all in the interests of Clean Energy, so chase around your government web sites on Google to find out. Assuming that you don't just go for the Simple Solution of converting your 120 VAC socket to 240 VAC
.
