Answers:
- You have a 60A breaker installed on a NEMA14-50 socket. That's vaguely illegal; such a socket is only really good for 50A. The general idea is that the breaker, the wire between the breaker and the socket, and the socket should all have the same amperage rating.
- Given that somebody did the installation, then there's all sorts of questions, the biggest one of which is whether the wire between the breaker panel and the socket is actually rated for 60A. Or 50A. Or whatever. Did whoever did this leave a note as to what AWG wire was used?
- Next: If your life wasn't complicated enough, there's this funny bugger thing about the NEMA14-50 socket and the National Electric Code. Apparently, people installing clothes driers that pulled down 40A (max) wanted to use the NEMA14-50 socket. So, somehow, it became legal to use (a) a 40A breaker, (b) 40A-rated wire, and (c) and NEMA14-50 socket, the latter of which is good for 50 A - but nothing else would be. Just so we're clear, here: Breakers are cute, breakers are awesome, and they save lives all over. But they're emergency devices: Sure, they're guaranteed to open a circuit on the first massive overcurrent, thank you UL, but, as a regular thing, they become decidedly unreliable. So, it's really a bad idea to depend upon a breaker to pop on a regular basis.
- Now comes the the deal on the wire. Say that whoever did the install used wire good for 60A. That's a big assumption. But, for the moment, say it's true. And you have this idea that you'd like to up the current into your Tesla by installing a Tesla Wall Connector (TWC) or some other commercially available wall connector for Juicebox or somebody. If you make a direct connection from the wire into your desired Wall Connector of choice, and the wire is really good for 60A, then you're all set. Put in the Wall Connector, leave the 60A breaker (which is protecting itself and the wire, it's not good to have wire get so hot it catches the house on fire and all) where it is, and you're good to go.
- Next: Suppose that the maniac who put that 60A breaker in there used wire that was good for X, where X < 60A. Then it behooves you to get that 60A breaker the heck out of there and replace it with a breaker that's also good for X. So, if it's 50A wire, then put in a 50A breaker. If it's a 40A wire (which would be another evil, because that's a NEMA14-50 50A socket), then it's a 40A breaker for you. If it's less, call the building inspector police on the guy because the sucker just tried to kill you and yours. I'm not kidding about "trying to kill", electrical house fires are a bitch.
- Next: You're using a UMC. That's cool. Probably with the NEMA14-50 adapter stuck in the end. Also cool. Now's the time to introduce you to the 80% rule: National Electric Code Says: Max steady load on a circuit is at most 80% of the breaker/wire/socket rating. That means if you're using the 120 VAC adapter (NEMA5-15), that gets plugged into a 15A breakered circuit. The UMC knows about the NEC: Max current draw at 120 VAC with that adapter will be 80% of 15A, or 12A. So, you're using a NEMA14-50 adapter.
- Tesla knows about the 80% rule. They also know that there are NEMA14-50 sockets that are backed up by 40A breakers. And the UMC, on its own, can't tell if it's 50A or 40A back there.
- So, right off: The most 240 VAC current you'll ever be able to draw with that NEMA14-50 adapter will be 32A, which is 80% of 40A. Safety first!
- On top of that: Max current the UMC will do with any adapter is 32A. Safety or no Safety.
- Next: Let's suppose you're playing with Tesla Wall Connectors today. They come in two flavors:
- Direct wired. If you have a modern Tesla that's Long Range or P, those cars have three (3), count 'em, three, 16A 240 VAC to internal DC voltage inverters. Such a car can pull down 48A at 240 VAC. I have one of those kinds of cars: I get 45 Miles of Charge per Hour. If you have a SR, that has a smaller battery, Tesla sized the inverters for the battery size. Instead of three 16A inverters, such a car has two 16A inverters. Maximum current one can draw is 32A. (Which, interestingly, is what the UMC can do..)
- Socketed. There are variants of the TWC that, instead of being wired directly into the breaker panel, have a NEMA14-50 socket on them.
- The good news: Easy to install. Bolt the TWC to the wall, put the wire into the NEMA14-50 socket, and you're there.
- The bad news: a) You're going to get a maximum of 40A (80% of 50A) charging. Worse than 48A, better than the 32A with the UMC. b) Make sure that the wire to that socket supports 50A. And you'll want to change the breaker, for sure, to 50A as well
A couple of points about Max Charging Current and such.
First: The UMC, TWC, or $RANDOM Juicebox or whatever has a microcontroller in it. Said microcontroller
talks to the car's computer and tells the car's computer how much current and voltage the UMC/TMC/Juicebox can supply. The car then looks at its navel, figures out how much current it can accept, picks the lowest number, and
that's the current the car will charge at.
How the UMC figures out the numbers is simple: It looks at the adapter that's plugged into it and figures it out from there. Got a NEMA14-50 adapter? It tells the car it's on a 40A circuit. Got a NEMA5-15 adapter? It tells the car, "120 VAC and 15A circuit". You get the drill.
A true-blue TWC has ways of being set. The direct-wired one in my house is a Gen II. One literally sets the switches in the TWC to tell it what kind of circuit it's hooked up to. Weirdly enough, one of the sets of switch settings is for 200A (!) service; apparently, early-model S's could pull down 160A or something. Mine is set to a 60A circuit (and, yeah, there's a 60A breaker on my panel), which gets me 48A (80% of 60A) charging.
My understanding is that current TWCs get their "switches" set during commissioning, using some kind of Web GUI. There's instructions in the TWC manual. So, if one has a socketed TWC, or the breaker panel supports at most a 40A breaker, or X, then the TWC is told that it's on an "X" breaker/socket/whatever, and that's what it communicates to the car. Very similar games are played with Juiceboxes et al. Once the CPU in the wall connector knows what kind of circuit it's on, it tells the car that info, and the car figures out how much current to draw.
So, let's summarize:
- If you have 60A wire, 60A breaker, and you install a direct-connected TWC (or whatever) that can handle 60A service, then you tell the TWC by switch or by GUI that it's on a 60A circuit. And you don't change the breaker, but you do ditch that NEMA14-50 socket. At which point, if you got the right car, you may get 48A charging. If you got the wrong car (i.e., SR-range), none of first part of this changes, but the car's only going to suck down 32A, that being all it's capable of. You still wouldn't have to change the breaker or anything.
- If you don't have 60A wire OR you're planning on using that NEMA14-50 socket, then you change out that 60A breaker for a 50A breaker. Or less, if the wire won't support 50A. You're going to have to turn the breaker in the panel off, get the cover off that NEMA14-50, and stare at the wires in there. If you're lucky, you'll be able to see the AWG size on the insulation. If you're not lucky, you'll have to measure the wire diameter. See here for a lecture on the subject; it looks like for 60A service you'd need a minimum of 4 AWG wire.
What you don't need to do, unless somebody put some really dinky (as in, completely unsafe) wire in there, is change your 60A breaker to 30A or something.
Let us all know how things are working out over there.
