EV charger wiring - sub-panel requirements

Question

I am looking to add a 30A outlet in my garage for the purpose of charging an EV. My home has 200A service coming through the main panel, and currently there are no sub-panels except one for the central air AC unit.

My dryer is located on the other side of the garage wall where I would like to place the outlet. When we bought the home, the previous owner had tapped into the dryer outlet and added a 240V outlet where I would like this one. This was not up to code, so we had them remove the outlet and plate over the box before we closed.

Fast forward a few years and I'd like to put an outlet here but do it right. I do NOT want to install a dedicated charger, but would rather install a 14-30 outlet that most any non-hardwired car charger can use, both for my current use and future-proofing.

I opened the box where the previous outlet was and found 10/3 wire w/ground (picture below), even though the dryer outlet on the other side of the wall and the one we had removed are both 10-30 receptacles, and so ungrounded (home was built in '92). Testing these wires confirmed two hots at 120V each, one neutral and a dead ground. Odd thing is, the bare copper wire which should be the ground wire is wired as neutral, and the white neutral wire is dead. A no-contact voltage tester indicates the bare copper has live but low voltage present. With a DMM, I get 120V from either hot to this wire, and nothing from either hot to what I thought should be the neutral. Is this normal, or am I doing it wrong?

I was NOT planning to just add a receptacle back where it used to be, tapped off the dryer. My plan is to add a 60Amp breaker at the main panel (about 25 feet away) and run 6ga wire to a subpanel in the garage, and within that panel add two 30A breakers, one to feed the dryer (with a proper 14-30 outlet) and one to feed the EV outlet (also 14-30), feeding both with 10/3 romex. I consulted an electrician about this and he said I only need a 50A breaker in the main panel for this setup(???). I may, MAY, elect to add a 14-50 outlet instead of the 14-30 for the EV outlet in the garage, in which case I'd upgrade that respective breaker and wiring as well as bump the 60A breaker to feed the sub up to 80. I'd cap off the existing run to the dryer, and yank out the wires the previous homeowner ran to the aforementioned garage outlet. I plan to do all this work myself, with the exception of the work at the main panel. I will hire an electrician (a different one) for that after I've wired everything else up.

I get that I could leave the current dryer setup alone and just add a receptacle on a dedicated circuit for the EV charging, but after seeing inside the box for the receptacle we removed I'm growing increasingly uncomfortable with how the dryer line was tapped, and I figure I'll just go ahead and update that to 14-30, and try to do it right. Does all this sound reasonable? I would greatly appreciate any input, insights, or comments.

Answer 1

I opened the box where the previous outlet was and found 10/3 wire w/ground (picture below), even though the dryer outlet on the other side of the wall and the one we had removed are both 10-30 receptacles, and so ungrounded (home was built in '92). Testing these wires confirmed two hots at 120V each, one neutral and a dead ground. Odd thing is, the bare copper wire which should be the ground wire is wired as neutral, and the white neutral wire is dead.

Yes, that's just the kind of horky nonsense we see anytime NEMA 10 is involved. In fact it's a bit of a surprise to find a groundless NEMA 10 in 1992, since groundless #10 wires were all but gone from the market. Some people installed 10/2 w/ground, and abused the ground as neutral; but that has always been forbidden (and thus, NOT grandfathered). Once old stocks of 10/3 "without ground" ran out, you were to use 10/3 with ground and simply not connect the ground if using a NEMA 10-30.

However, one thing was legal: having multiple outlets on a 30A circuit.

I was NOT planning to just add a receptacle back where it used to be, tapped off the dryer. My plan is to add a 60Amp breaker at the main panel (about 25 feet away) and run 6ga wire to a subpanel in the garage, and within that panel add two 30A breakers, one to feed the dryer (with a proper 14-30 outlet) and one to feed the EV outlet (also 14-30), feeding both with 10/3 romex

Well, 6/3 Romex (NM or UF) is only good to 55A, but I wouldn't use it anyway. They don't make that breaker size, so you're free to either "round down" or "round up". Code requires that you provision a subpanel feeder "sufficient for the load to be served", so you couldn't plan to use more than 55A. The EV charging requires a 125% derate on the maximum current the EVSE will authorize, so 24A max programmed charge rate requires 30A provisioning, 30A wire and 30A breaker. So you would be counting on the dryer being <25A actual.

I wouldn't use it because you can get more suitable feeder for <1/2 the price, as manassehkatz discusses. #2AL feeder is about the price of 10/3 Romex. Large feeders work best as aluminum - long history has proven its reliability and economy (and the lugs you'll be attaching to will be aluminum). Part of its secret to success is electricians have always used torque wrenches to set large lugs. As far as stiffness, AL is about the stiffness of the next size smaller copper (so akin to #4 Cu).

90A will cover present and future EV charging to 60A+ your dryer simultaneously, and if you can avoid simultaneous dryer use (or certain tech solutions were are expecting soon), you can run 80 or 90A shared between two EVSE's, which is pretty much the "state of the art" for EV charging.

Answer 2

The old wiring is 100% irrelevant to this, since you know it isn't large enough for anything more than 30A. So ignore all that and the plastic box, etc. Except that you should replace the existing 30A dryer 10-30 receptacle with a 14-30 receptacle, which will be easy since the new subpanel will have ground going back to the main panel. You will need to change the dryer cord and remove the neutral/ground bond on the dryer.

Back to the main issue: subpanel. That is the right way to do it. Better than 6 AWG copper is 2 AWG aluminum, which should get you all the way up to 90A! You don't have to install a 90A feed breaker - any size large enough for what you plan to use in the subpanel is fine, but no larger than 90A. You can always change it later.

I am fairly certain that the subpanel is not required to have a main breaker. If it were in a separate building then a shutoff would be required, which a main breaker would satisfy. But a main breaker for convenience when working on the panel is just fine if you want to have one. If you have a main breaker in the subpanel, any size >= the feed breaker size is fine. You can have a 100A breaker with a 60A feed.

You probably don't need a huge subpanel, but you should always get larger than you think you need. You should certainly have enough for:

• 2 EV chargers (Tesla + Ford, based on comments to another answer) - 240V
• Dryer - 240V
• 1 receptacle circuit - 120V
• 1 lighting circuit - 120V

which is 8 spaces. But bigger is better. Maybe someday you'll want to build a shop (240V tools) or do other things with the space. Also keep in mind that many circuits, especially in garages, require AFCI and/or GFCI, and those won't work in 1/2-size spaces. If a panel says 20 spaces/40 circuits, treat it as 20 spaces/20 circuits.

As a semi-random example from Home Depot (your local pricing at various sources will vary, of course), there is a Square D Homeline panel currently selling for < $100, in stock in at least some locations (i.e., not some "can't find it anywhere due to supply shortages" thing) with 24 spaces ("48 circuits" - ignore that), 3 x 20A single pole breakers, 2 x 30A double pole breakers (one of those will be for your dryer). You'll need to add more breakers, and you may need a ground bar (not sure, haven't checked the specs in detail) because this is being installed as a subpanel. But compared to everything else (particularly the cost of 25' of 6 AWG copper, though hopefully you'll be able to switch to cheaper aluminum) this is "nothing" and provides lots of room for the future. Also keep in mind that the biggest drawback to any subpanel (instead of individual receptacles going back to the main) is making sure you have code-required workspace in front of it. But that will be the same for any panel, so might as well go big.

Don't worry about aluminum. The problems with aluminum is with small circuits. Done properly, aluminum is perfectly fine for large circuits. There are restrictions in some places (at least Montgomery County, MD) with aluminum for branch circuits, but not for subpanels.

Answer 3

Do consider future usage - the car several generations away might have 50A or more of charging capacity.

A future car might be capable of reverse-feeding your home at certain peak times of the day as part of load-shifting.

I would suggest exploring the possibility of a completely separate circuit just for charging cars, AND how much the opportunity cost is to ridiculously oversize that circuit.

None of us know what the next decades will hold in terms of vehicles and energy management in the home. If the incremental cost to go up in capacity is small, it may be worth doing now.

Answer 4

First of all, if that dryer outlet was for a 220v only dryer, that configuration would be correct. They probably just only had that wire type available. You only need the neutral connected if there is a 120v requirement as part of your device. Otherwise 220v plus ground is all that outlet needed. And it would be absolutely correct to read 120v between each leg and ground. Remember that your neutral wire is grounded at your main panel in standard configuration, so with no current flowing they will measure about the same.

Now, about your car charger:

1. Don't use aluminum wire without knowing the code in your area.

2. If you don't NEED 90A, then you might not want to spend the money for 2/3 AWG.

3. IF 50A will do it for you (actual draw being 30A), just install your disconnect on the existing wire and connect a suitable outlet.

4. Remember, depending on how the chargers you will be using are configured, you might WANT to connect a 4 pin outlet, 2 of the pins being 220v "hot" with the white neutral connected to the 3rd pin and the real earth ground connected to pin 4 (with the notch). Otherwise, if your charger just calls for 220v and ground, it would be connected just as your predecessor had the outlet wired (with the white "neutral" wire not connected at either end).