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I bought an electric car and now hope to install a Tesla Wall Charger that needs a 60amp/220V Circuit, or alternatively I will install a 240v NEMA 14-50 (50a) plug. I would prefer to install the Tesla Wall Charger, as it adds ~+12 miles per hour charging (42 KWH).

I am hoping to tie into a 125 amp subpanel in our garage that I used for our house remodel. There are many breakers/circuits in the subpanel, so don't know if this will fly. The subpanel is supplied by a #2 copper wire (2/3 Romex) with a 125 amp breaker in the main 200 amp panel. Will it be possible to tie into the subpanel or do I need to run a separate line from the main panel? Trying to avoid making the run from main panel as it will be about a 50 foot run. Thanks for any thoughts/suggestions you have.

The list of current breakers in the subpanel are below. The charger will be programmed to run non-peak from 12 am to 7 am, so only a few of the circuits will be energized at the same time (refrigerator and possibly some lights and outlets).

Thanks for any thoughts/suggestions you might have!! Rob

Description of Breakers (from bottom right to top):

  1. Family room outlets 20a AFCI
  2. Kitchen Oven (220V 50a) +#4
  3. Living Room outlets / HVAC outlet (Double 15a)
  4. Hall Outlet / Office Outlet (Double 15a)
  5. Exterior Outlet (20a)
  6. Hall Lights / Exterior Lights (double 15a)
  7. Living Room Lights/Dining Lights (Double 15a)
  8. Kitchen Lights / Family Room Lights (Double 15a)
  9. Refrigerator (20a AFCI)
  10. Dishwasher (20a GFCI)
  11. Microwave / Disposal (Double 15a)
  12. Kitchen Outlets #1 / Kitchen Outlets #2 (Double 20a)

Subpanel Breakers

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  • Will depend on the load calculation. While you can use the 125A breaker because they don't make a 115A breaker, you can't provision more than 115A of calculated load here (75 °C ampacity for #2 copper). But you can limit the load of the car charger (on the car charger)...
    – Ecnerwal
    Jun 2 at 11:48
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    How many square feet of space does this panel serve, and what's the kW rating on the oven connected to it? Jun 2 at 11:48

2 Answers 2

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EV charging tech is actually pretty slick.

I bought an electric car and now hope to install a Tesla Wall Charger that needs a 60amp/220V Circuit, or alternatively I will install a 240v NEMA 14-50 (50a) plug. I would prefer to install the Tesla Wall Charger, as it adds ~+12 miles per hour charging (42 KWH).

First, EV charging tech is pretty slick, and allocates charge current "soft", i.e. the current is programmable. The main job of the Tesla Wall Connector is to tell the car how much current it is allowed to take. It's not actually the charger. Really.

So when you install a Wall Connector ("Commission" it), you configure the amps of the circuit, which can be any value - 20, 30, 35, 40, 50, 60, even 80 amps. So you can definitely use the Tesla Wall Connector, you simply set the value your house can support.

And if you get a second EV, the two EVs will share this allocation using technology everyone else calls "Share2". It's very cool.

But wait. How much can your house support?

You described all your breakers, but unfortunately that was a waste of time. You must follow a procedure called a Load Calculation which is defined in NEC Article 220. That procedure does not care much about 120V breakers.

Your municipality will have a worksheet which they derived from Article 220. I find a great deal of inconsistency among those from municipalities, so I would ask your own local municipality for their rules (they may have a worksheet). All of them include a) 1500 VA for each of your kitchen general appliance circuits, and laundry room circuit and b) 3 VA per square foot of finished space (so not attic or unfinished basement). Fixed-in-place 120V loads (disposal, dishwasher, built-in microwave etc.) take their nameplate VA (volts x amps). Then 240V loads get a demand factor applied.

Anyway, here's the thing. You must do the Load Calculation twice:

  • On the entire service
  • On the loads and square footage powered by that subpanel

The lesser of the two will indicate the amps you can commission when you set up the Tesla Wall Connector.

Note that Tesla Wall Connectors don't actually use neutral (their recommendation of NEMA 14-50 is so you can also use it for an RV, which does need neutral). You are better off hardwiring if you can.

Also note that #6 copper NM and UF are only good to 55A, not 60A.

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  • That dynamic current limiting happens only with chargers equipped with the current sensing clamps that go around the feed into the house (which makes them harder to install). The cheapo wall units may not have that and only signal a constant current limit. Jun 3 at 10:07
  • The load calculations are only needed one time if done a pro will just make measurements as is allowed in most states.
    – Ed Beal
    Jun 3 at 15:45
  • @EdBeal How are the measurements done? Do you leave equipment there for a few days? If the utility will give you KWH used hour by hour, is that enough? (on this last point I am highly skeptical, but a novice insists that is OK.) Jun 3 at 18:11
  • With electronic meters and a report from the power company that is all that is needed, if the peak load is 120a there is 80 available, when I test I turn everything on run the hot water and turn the heat or AC on watch it for a few minutes to catch the peak and the same thing. With modern power meters if your utility has remote access they usually have real time monitoring or the peak value every 1,2,3,4 hours depending on the rate. I have coached friends on the same and they were able to pull a permit and do the upgrade themselves legally and no issues with code.
    – Ed Beal
    Jun 3 at 19:33
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Based on the breakers you have I would say yes you have the ampacity to add another 50 amp load. your only large load the oven and even with this we don’t just add the breakers with 200 to the main I might revise the answer if all electric home as far as heat or if an on demand electric water heater was in the main panel then my answer would be maybe to no. With the load in the sub there is enough available with a 125a feeder.

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  • Thanks for the comments!! The subpanel serves approximately 800ft2 of space. The oven is a dual fuel (gas burners and double electric oven). The stove power/ratings for KW at 208V/240V are 6kw/6.9kw. The home is gas heated. Water heater and dryer are both gas, as well. Could I squeek out the 60amps for the Wall Connector or would it be advised to stick with the Nema 14-50. I guess I could also make the 50 foot run and free up future space in the subpanel.
    – RobSLO
    Jun 2 at 15:34
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    I would stick with hard wire because the 14-50 requires GFCI protection and the charger has this built in , do you need anything larger than the feeder requirements? A smaller wire size is possible but would need to verify with the mfg installation instructions I would probably use a 50 amp bkr if allowed with #8 copper but that goes back to the actual load requirements.
    – Ed Beal
    Jun 2 at 16:40
  • Hi Ed, Thanks again!! The two options I have are using something called a mobile charger that would plug into the NEMA 14-50 outlet. The mobile charger comes standard with the car andonly needs the 14-50 adaptor. Tesla recommends a 50 amp circuit (breaker) for the mobile charger option. It charges the car at approximately 30 miles per hour. The Wall Charger has a few more bells and whistles (wifi), comes with a more durable and weather proof cable/plug and charges faster, so long as you give it a 60 amp breaker/wire. I would definitely hardwire this.
    – RobSLO
    Jun 2 at 22:52
  • I prematurely sent the last message. The question I still have is could I use a 60 amp circuit coming out of my subpanel or is 50amp all I could reasonably get out of the sub, given the current load on that subpanel If I can't get 60, would it make sense to run a line to the main panel for the faster charging wall panel.
    – RobSLO
    Jun 2 at 22:55
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    With gas heat I would go with larger wire and a 60 amp in reality unless the charger was at peak load and the oven was also at max that would be about the only time there might be an overload with the lights and outlets in use. just don’t charge the car while cleaning the oven with all the lights on. Normal loading I would slap an amp clamp on the service and the sub to see the actual load but I am a professional and have actually done this work most 200A services actual average load is between 75-125 of the ones I have checked and with gas as you have it is usually lower by about 1/2.
    – Ed Beal
    Jun 3 at 15:44

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