TLDR: When you do the Commissioning Procedure for the TWC, choose "30A breaker". Or, do a bunch of NEC Article 220 Load Calculations and upgrade stuff.
We see a lot of misconceptions about EVs, that often lead people to very costly work they do not need. If you already are using a NEMA 14-50 you have already experienced some or this for yourself: your car finishes charging before you even go to bed, often before dinner is finished. Here is the X-factor:
EV charge rate is adjustable.
The EVSE (what you call a charger, it's not, it's just a smart GFCI) that tells the car what amps it can safely draw here, and the car adjusts to comply. Really. Here's an excellent video on the nuts and bolts of it.
I gather you've been using your Tesla travel unit? That comes free with two dongle plugs. They actually make 6 others for various amperages. Each dongle has a microchip inside that tells the car the amps of the plug! Really. That's why they're $45.
But they give you the 14-50 for free since it's found at RV parks (a "Hail Mary" place to fast charge, back before Superchargers everywhere). Remember that unit is for travel. This created a huge misconception that level 2 charging must be 50A and use a neutral wire. Not at all!
This is an upgrade in load for this line, as TWC can draw up to 48 amps and requires a 60 amp circuit breaker on this line.
Not accurate. The TWC can use any circuit ranging from a 15A to a 60A breaker. The breaker size is set during the Commissioning Procedure stated in the installation instructions. The TWC will then tell the car the safe amps on that circuit.
And that's a good thing, because you are overloading this panel as things are now.
How much power do you really need?
Like I say, you know perfectly well how fast your car charges and that even the "50A" (40A functionally) circuit is overkill for your daily needs. So the 60A tier charging is not a "need", it is a "want". Recognize that and look at what you do need. Alec from Technology Connections has a great video on that too. TLDW: a 20A circuit will be enough in most cases, and a 30A is plennnnty.
I hate these conversations where I have to walk someone back from big aspirations, but the fact is you don't need it, and you've been already overloading that panel and taking chances that may affect your insurance coverage.
I have no quarrel with a big charger if you've got room for it, but you don't. That's another "misconception" we see from EVers: that you can simply ignore your Load Calculation because you have a nice new car.
How much can you have?
That is decided by a NEC Article 220 Load Calculation - or rather, two of them. I say it that way to emphasize that NEC Article 220's procedure is the only valid way to do a Load Calculation, and you don't get to "freestyle" your own way (amateur methods always reach the same conclusion lol, one guess what it is!)
The first Load Calculation is on the entire household service. That assures the service can handle the load. We don't have nearly enough info to calculate that.
The second Load Calculation is on the subpanel, and here we have a pretty good shot (of finding numbers; the numbers are bad news.)
- We start with square footage of the area served by the subpanel. Let's call it 333 square feet. 3 VA per square foot must be allocated for general lighting and receptacle loads. 1000 VA so far.
- The bathroom circuit is swept into that catch-all.
- The washing machine and disposal use their nameplate data. For discussion let's take typical values of 1300 VA nad 700 VA (I'm making it round).
- The laundry and the four kitchen/dining general receptacle circuits each get 1500 VA.
I'm getting 10,500 VA. Most cities let you take "35% of the amount beyond 3000 VA" for this type of loads, so 3000 VA + 35% of 7500 VA gives 5625 VA.
EV charging applies as 125% of actual ampacity but the EVSE will take care of this for us, by only allowing the EV 80% of breaker trip.
6 AWG NM or UF cable is only 55A rated as is #6 wire outdoors in LFMC. This gives it 13,200 VA (55 x 240).
6 AWG other types allow 14,400 VA (60 x 240).
So I see either 8775 VA (36.5A) or 7575 VA (31.7 amps) available for EV charging. That indicates a 30A or 35A "breaker setting" in the TWC configuration.
Again, this is plennnty.
But we're not done. We need to do another NEC Article 220 Load Calculation on the entire house. I'll leave that to you. The EVSE must be the lesser of the two Load Calculations.
Set the EVSE to 30A according to this
You can go ahead and use the existing 50A cable (6/3 is it?) and simply cap off the neutral wire. When commissioning the Tesla Wall Connector, tell it that it is on a 30A breaker. (or if you are sure the wire is rated for full 60A, 35A breaker).
It is my opinion that having commissioned the EVSE for 30/35A, you can leave the breaker at 50A. Your inspector might contradict me, in which case don't fight over a $12 breaker lol.
"I want more, though! And my main can support it."
Are you sure? The thing about driving 250 miles a day - and I do this a lot - is #1 you pass a lot of Superchargers. And #2 you need human stops - food, drink, bathroom and to stretch your legs. Running into Starbucks is enough time to slam 100-200 miles into a Tesla, depending how long you dawdle. And I love to dawdle. My life isn't Indy pitstops.
And again, you can try it on for size. You're not marrying 30A. Commission it this way today, and it just doesn't work for you then you can change it. It's just wire and a breaker.
Okey dokey. The first thing we'll need to do is upgrade the feeder from the main panel to the subpanel. Now there's an amazing value here called #2 aluminum. There is nothing wrong with aluminum wire at these large sizes. In conduit use THHN or XHHW. Or indoors, use SER 4-wire cable. If you don't like it, use #3 copper. Of course both copper and aluminum will fail if you don't torque lugs to spec, so make sure you do that. It is irrational and anti-science to fear aluminum and then not bother to torque.
#2 aluminum is 90A wire. #1 aluminum or #3 copper is 100A wire. Select that breaker. That will bring enough power to the subpanel to go full 60A to the EVSE.
Then, upgrade the wire from subpanel to EVSE to either 6 AWG copper any type other than NM or UF, or, 4 AWG copper NM or UF. For instance 3-wire SER or SEU will be fine. This will get you 65A or 70A wire, respectively. Must be copper because the Tesla Wall Connector specs copper only.