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I am looking to add a 240v 50amp outlet to my garage for charging the EV. With the help of folks on this forum I found that I need to expand my subpanel to add more breakers before adding a line to the garage.

I have a main panel (200amps) and a sub-panel (100 amps). They are both full. Can I replace four 15amps breakers with 2 multipole breakers to open two slots in the subpanel?

Here is what the main panel looks like: enter image description here

Here is the subpanel: enter image description here

On this subpanel can the slot #3 and #4; and #6 and #7 be merged with multipole breaker? If yes, I can bring two circuits from main panel to this, and use the main panel's two open slots to add a 240v 50amp circuit. Will this work and be safe?

If not, is upgrading the subpanel the only other option?

Thanks for all your help!

Here is the picture of the subpanel breaker from bottom. Shows the brand. enter image description here

Here is the outside main panel. enter image description here

Panel and sub panel using the 10 gauge wire: enter image description here

enter image description here

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    Just checked - it is square d but no label on the top. Adding the picture.
    – adadevil
    Jun 24 at 22:44
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    How many square feet of space does your subpanel serve, and how many watts of heating are attached to it? Also, can you post photos of your main disconnect please? (It's most likely next to your electric meter, outside) Jun 25 at 3:04
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    @adadevil What size breaker and wire feed the sub-panel?
    – nobody
    Jun 25 at 12:57
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    Adding a 50A EV charger there probably won’t fly. You’re likely to to trip the feed breaker in the main panel if there’s much of any load on the other subpanel circuits (looking at you, electric heat). The good news is it’d be pretty trivial to rip out that tiny subpanel and replace it with a bigger QO panel so you can reuse all the existing breakers. You’d have to upgrade the feed breaker and probably the wire as well - someone else will advise on that.
    – nobody
    Jun 25 at 14:30
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    There should be more markings on the feeder wire - the part photographed is “with 10AWG ground” - grounds on large (~50A+) circuits are allowed to be smaller than the current-carrying conductors. On a 50A breaker, copper NM as you have should be 6Ga.
    – nobody
    Jun 25 at 14:32

2 Answers 2

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Looks like you're on the hook for a new main panel

Your problem is threefold. First, your main panel is full to the brim with double-stuff breakers, which means that there's no room for an EV breaker there. Second, since the subpanel feeder comes off the main panel, which is full of double-stuff breakers, the largest feeder you can run from your current panel is 50A as larger double-stuff breakers aren't a thing. Finally, you'd be limited to a paltry 30A if you tried to run the charger from the subpanel as QO double-stuff breakers top out at 30A instead of 50A to begin with, despite the subpanel feeder being (presumably) capable of 50A.

So, you'll need to replace that whole main panel with a new, larger panel. Fortunately, the fact your main disconnect is outside, separate from the panel, makes this a fairly reasonable DIY job. The new panel of choice for this will be a TLM4020C80G; this provides you with an additional 20 full-size spaces over your current panel, which is enough to accommodate future GFCI/AFCI upgrades, your car charger, and a larger feeder to an upgraded subpanel, while allowing you to "transplant" your existing circuit breakers for the time being.

Note that in order to make sure the car charger won't overload your main panel, you'll have to do a NEC Article 220 load calculation to make sure you have the 40-50A of wiggle room required for a Level 2 EVSE. For this, we'll need the square footage of the whole house, as well as the nameplate ratings of the air conditioners, range, disposal, and Jacuzzi.

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  • Trying to understand this a little better. If I end up replacing the main panel, will this panel work? I could not find TLM4020C80G in stock. link Also, will the existing breakers work in this panel or will I need to buy all new breakers?
    – adadevil
    Jun 26 at 11:30
  • Also, I am planning to do the load calculation today to make sure that I can add 50amps circuit.
    – adadevil
    Jun 26 at 11:31
  • @adadevil -- there are a couple of sub-variants of the TLM4020C80G -- the G2 is the one listed in GE/ABB's catalog, while Home Depot should have the GK version available for order (even if your local HD doesn't stock it). Note that what you linked is the TM4020C80K (note the missing L and G in the part number) -- it's a main breaker panel, not main lug (which is $10 bucks you don't need to be spending) and doesn't come with grounding bars fitted (you'd need to buy them separately, which is another $10-$20 you wouldn't need to spend) Jun 26 at 16:15
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Your sub panel is listed for doubles 6/12 the problem I see is the main panel the largest breaker is 50 amps so there will need to be a change for the breaker and feeder, now comes the normal news for heavily loaded panels.

You will have to do a complete load study or have it done by a pro, it looks like your home was a custom job by the number of the circuits and a standard load calculation that may be suggested would not be acceptable due to the number of circuits.

A load study is basically finding the peak loading and some jurisdictions will allow power company peaks as the value, if your peak value is around ~130 amps you could add the EV charger.

From what I see the sub is only fed by a 50 amp circuit so this will need to be upsized (breaker and feeder wires)

So in any case the minimum needed will be a larger breaker for the sub and a larger feeder when going this far I would suggest a larger sub panel I love square D but there tandems and quads are more expensive and dropping a full side panel is usually less expensive.

If you are over ~130 peak then a service upgrade is required. Where do I get the 130 amp peak? You can only use 80% of the unused amount of a service so you need about 62.5 because of the 50 amp but most jurisdictions round up to 70 in this case I have done many of these over the years by turning everything on heat or AC the larger and taking measurements .

Looking at your panel I would bet you have the available especially if you have upgraded to LED lighting.

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