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I have NEMA 14-50 in my garage, and would like to install Tesla Wall Connector (TWC) using the same line. 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. Also, big difference with other EV chargers that it has to be hard-wired (and so NEMA 14-50 or other outlets can't be used).

Currently a subpanel has a 50amps circuit breaker for this line --

subpanel

This subpanel is fed from the main panel, and has a 60 amps circuit breaker --

main panel

Subpanel has a few other circuit breakers as you can see on the first photo, not just the charger:

  • kitchen outlets (x 3)
  • bath outlet
  • washer
  • dish washer
  • garbage disposal.

So it's roughly 10amps left to all of the above (60 amps minus 50 amps, difference between the two circuit breakers).

Question: what circuit breakers I should use if I upgrade NEMA14-50 to a Wall Connector? I think it should be:

  • main panel's circuit breakers 60 amps -> 70amps for the subpanel;
  • subpanel's circuit breakers for the EV charger 50 amps -> 60 amps.

The main panel's main circuit breaker is 200 amps, and so it should be sufficient for the combined load.

Update: same thread on TMC forum -- https://teslamotorsclub.com/tmc/threads/upgrading-panel-and-subpanel-to-have-a-wall-connector.293411/#post-7401868

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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.

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  • One tiny tweak: there is a slight possibility that even types other than NM may not be good for a 60 amp circuit. I know because I ended up having to go through a box that is only rated for 60C when in a wet location. You can use the 75C number if everything involved is rated for the higher temperature.
    – KMJ
    Commented Feb 8, 2023 at 3:12
  • @KMJ yeah, good point. LFMC probably. Commented Feb 8, 2023 at 3:20
  • "anti-science" - that's a great phrase for those who insist that we must "follow the science" and that "the science is never wrong". I like it!
    – FreeMan
    Commented Feb 8, 2023 at 15:03
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First of all, a hardwired Tesla Wall Connector is a very good idea. It is a quality piece of equipment, designed to be hardwired (my preference for lots of other things too - ovens, disposals, dishwashers, etc. - hardwired has a number of real advantages over cord/plug connections).

However, you're mixing up a few different pieces of the equation, all of which matter to varying degrees:

  • Total service/available capacity in the entire house. This is nominally 200A (main breaker). How much capacity you have available for EV charging depends on 200A (service/main breaker) minus a real load calculation. Odds are that if you don't have a really big house, you don't have lots of bitcoin miners or other large constant loads, don't have on-demand electric water heating (gas on-demand or regular, or electric regular are all fine) and don't have electric resistance heating (heat pump is fine, gas is fine) then you probably have 30A - 50A available. But the only way to know for sure is to do a calcuation.
  • Subpanel available capacity. Again, a load calculation (this time based on just the circuits in the subpanel, not counting the charging circuit) is the key. Whatever is left (60A - 'x') is what you can safely use for EV charging. That might be 50A, but more likely far less. My guess is around 30A.
  • NEMA 14-50 vs. hardwired. Reuse the circuit for the hardwired EV service equipment (a.k.a., "charger"). Since the 14-50 is nominally for charging and you have no other use, you take it out, use the junction box to connect to the EVSE. Done, except for determining how much power to provision (which is based on the load calculations).
  • You can't upsize breakers without upsizing wire. It is unlikely (but possible) that the subpanel feed or the 14-50 feed has larger wire than the current breaker size. But if it does then you can upsize. Or alternatively run new, larger, wire/cable. That may be useful for the subpanel feed. For example, if load calculation for the house gives you 50A or more capacity for EV charging but subpanel gives you 20A, it may be worth upgrading that subpanel feed so that you can upsize the breaker and use more of the available capacity. How hard it is to do that will depend on the distance between the panels and how hard it is to run new wires (easy if you have large conduit, easy if just one wall in between, hard if cable run across the whole house, etc.)
  • The Tesla EVSE (and most others) can be set to any capacity up to the limit. There is no need to set it for 60A (48A usable because of continuous use derate) or even 50A (40A usable) or 40A (32A usable). For typical daily usage (not driving Uber/Lyft all day or 150 mile round-trip commute), 30A @ 240V or even 20A @ 240V is sufficient. 30A @ 240V adds around 20 miles of range per hour of charging - so an 8 hour charge adds around 160 miles of range. 20A is 2/3 of that, but still enough for most people, most of the time. In other words, if your load calculations result in at least 30A, set it for 30A and you're done. If you load calculations result in between 20A and 30A, set it for 20A and you're done. Only if your load calculations result in < 20A do you really need to look at upgrades to service or feeds (likely the feed and breaker from main panel to subpanel).
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  • I'm surprised the breaker isn't already popping breakers. It's way over the load calculation based on the circuit labels there.
    – KMJ
    Commented Feb 8, 2023 at 3:09
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    @KMJ Actually, it isn't. It is only way over if the 14-50 charging circuit is in use. Otherwise it is nominally 20 x 8 = 160A @ 120V but split so 80A @ 240V, which is only a little above the 60A feed breaker. More importantly, if those labels are correct then most of those circuits are lightly loaded most of the time - disposal probably 10A - 12A but only a few minutes a day, bathroom 15A for a hair dryer but a few minutes a day, dishwasher 10A - 12A but only an hour a day, etc. So only when "all at once" is it an issue. But load calculation might say "all that's equivalent to 30A @ 240V" Commented Feb 8, 2023 at 3:17
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    or whatever (making that number up out of thin air) and then you take 60A - 30A = 30A = 24A continuous for charging. It isn't perfect (because who knows when you'll want to make toast and dry your hair and wash dishes and vacuum the dining room carpet etc. all at the same time) but basically load calculations work pretty well. Commented Feb 8, 2023 at 3:19
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    It's way over the calculated load. In the real world it might be OK, for exactly the reasons you suggested. I wouldn't bump to a 48A charging load though!
    – KMJ
    Commented Feb 8, 2023 at 3:19
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    The Leaf wouldn't be over 32A. Similarly, the current Mobile Connector for a Tesla is also limited to 32A.
    – KMJ
    Commented Feb 9, 2023 at 4:15
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The Tesla Wall Connector (like many EVSEs) is configurable: it supports passing through up to 48A (when fed by a 60A circuit) but you can also tell it that it's on any smaller circuit size, all the way down to 15A.

As long as the existing wire is correct for 50A, you can tell it that it's on a 50A circuit and it will tell the vehicle to draw up to 40A. If that much draw, combined with all the other circuits in your sub-panel, trips the breaker feeding the sub, you can bump it down a notch or two. Unless you drive a lot (or can't/don't charge every night) you will probably find that you can replenish your daily usage with a charging rate as low as 16A (20A circuit).

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  • I'm not sure that "set it high, see if it trips a breaker, then bump it down" is really the right way to go about provisioning the EVSE...
    – FreeMan
    Commented Feb 8, 2023 at 15:06

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