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I am on the brink of purchasing my first EV, and I have an electrician coming by this weekend to give me a quote for a charger install. Here are the details:

  • 100amp panel
  • Gas furnace, stove, hot water heater, dryer
  • My electric utility uses a smart meter that is able to show usage data. Over the last two years, my peak usage was 5.90 kW.
  • 20 slot panel BUT they're all taken.
  • Want NEMA 14-50 plug-in charger on a 50amp breaker
  • Panel and garage are on opposite sides of the house, and the panel is in the basement which is finished. So not an easy run and would require drywall patching and painting.

Knowing all that, I believe my 100amp service is sufficient, but that I may need to shell out for a larger panel with 24+ slots. I've read there are people with 100amp service that are able to install EVSEs without issue...do you think this is doable in my situation?

Alternatively:

Is it possible to run a wire directly from the meter? Here's a picture of my meter.

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In the photo, you can see that the main breaker for my panel is there, but there looks to be a slot above for another breaker that could run out to the EVSE. Is that doable? If so, is it a huge code violation? If there aren't any issues, that could save me from getting a panel with more slots and tearing up my basement.

I obviously will run all this by the electrician, but I just want to be somewhat educated when speaking with him. Thanks for the advice.

EDIT: I've just wanted to add some photos of my panel

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  • 2
    A plug in will probably require GFCI protection, can get expensive and hard to find. Hard wiring the charger to the panel/breaker does not need GFCI protection.
    – crip659
    Oct 8, 2022 at 11:52
  • Do you have air conditioning?
    – JACK
    Oct 8, 2022 at 12:47
  • Yes, I have a 3ton 14SEER unit. So when that's on, it's using ~3kW
    – RobbyV
    Oct 8, 2022 at 13:17
  • 1
    Can you post photos of the panel in question please? Oct 8, 2022 at 18:31
  • 2
    You need to do a load calculation — or your electrician should have to do one. Oct 9, 2022 at 0:04

2 Answers 2

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A number of misconceptions common to EVs

It won't surprise you that we have a lot of EV first-timers coming through here with electrical questions. In my observation, almost every one arrives pre-misinformed.

  • You don't, don't, don't need a 50A circuit to charge an EV. A 20A/240V (3.8 KW) circuit is adequate and a 30A circuit is downright luxurious. Really. Listen to a technology master and EV veteran, at 34:26. Stated clearer at 28:16.
  • This will help solve a serious problem with your service.

"Notice how the smallest number I gave you was 100 miles. I really need you all to know this, and deeply -- A 20A circuit run with yellow Romex can make even a crossover-sized EV like mine charge 100 miles every single day, charging exclusively overnight. You do NOT need a giant charger."

--- Alec from Technology Connections.

  • That charger (EVSE) they "toss in" with the car is a travel charger intended to live in the trunk and be used for opportunity charging "on the road". Therefore it includes a dongle plug for the most common outlets on the road: The normal one, and the standard RV/motor-home socket. so you can charge at RV parks or friends with RVs.
  • Noticing this socket, EVers leapt to the misconception that this is some kind of "standard EV socket". No it's not, it's the standard RV socket. EVs don't use neutral, so that would be a silly choice that would be unnecessarily costly to wire.
  • This is also where the myth of 50A charging came from. It's nonsense, people got it off these free "thrown in" travel chargers and their RV sockets. Note that since that same NEMA 14-50 socket is also used on 40A circuits, the travel EVSE with the 14-50 dongle will limit charge to 32A. So you're not even getting your money's worth.
  • Hardwired wall units are strongly preferable, as they are easier to work with, and allow peak charging performance. For instance your car probably has a 48A (60A circuit) or 80A (100A circuit) internal limit. To hit that, hardwired/wall unit is your only option. If you're OCD like that. As Alec discussed, it's not needed in the real world.
  • Hard-wiring the EVSE also avoids a costly socket (quality matters there) and an even more costly and redundant "stupid GFCI" breaker in your panel (these breakers also take full spaces, by the way). EVSE's already contain a "smart GFCI" that will self-reset, so adding a stupid GFCI breaks that feature.
  • Hardwired units are also eligible for rebates/government assistance. Plug-ins are not. Between that, the costly socket, the largely wasted 6/3 wire, and the fat GFCI breaker -- the hardwired unit may be cheaper.

I know it's not fun to find out you were misinformed. However I hope you notice the opportunity that is arising to do this right without a service upgrade.

But Sometimes!

A lot of naysaying happens around edge cases. "Who knows? One day my battery might be at 25% and I'll have a 200-mile day tomorrow. I need a huge charger every single day on that off-chance."

Well, here's what you do then. On the way home before, you stop at a DC fast charger for literally ten minutes. By the time you're back from Panera Bread with your pastry, it's lifted from 25% to 65%. You now are within 100 miles of full, and your home unit easily handles it.

Armed with some tools, let's tackle the elephant in the room.

You haven't given us a rundown on all your large appliances, but I've never seen a 100A panel in my life that had room for 50A of EV charging. That does not happen. And by the way, this is decided by a NEC Article 220 Load Calculation - you don't get to spin your own method. Article 220 is confusing, but many municipalities have worksheets.

My electric utility uses a smart meter that is able to show usage data. Over the last two years, my peak usage was 5.90 kW.

Not useful. The smart meter takes interim meter readings every 15 or 30 minutes. This is saying "in this 30 minute period, your load averaged 5.90 kW, and that is the highest 30-minute average this month". Interesting for billing, but useless for safety.

This is about safety.


However, go back to Alec's "Know this, and deeply": 20A @ 240V is all you really need. I am confident you will be able to fit a 15A, 20A or 30A circuit in there. Even 15A isn't the end of the world: at 240V, 15A is still 75-90 miles a 10-hour night, and most nights will be longer anyway, right?

But how do we get to it? The travel EVSE only comes with a 120V/15A or a 240V/50A socket.

  • Some manufacturers sell NEMA 6-15, 6-20 or 14-30 plug dongles for the travel EVSE. Tesla wants $35-45 for theirs. Those automagically tell the EV that they are on 15A, 20A or 30A circuits (a microchip is embedded in the plug).
  • You can go with a wall unit, and when you commission (configure) the unit, you set the DIP switches to tell it what circuit size it's on.
  • If your vendor's wall units are not configurable (like Cripple Creek), then you buy the unit of the correct amperage.

There is one "Hail Mary" play that is possible even if you have no room in the Load Calculation. An interesting fact about NEC is that there is no limit to the number of general purpose sockets on a 30A circuit. Users are expected to have discipline. So assuming you have an electric dryer circuit that has both neutral and ground wired to it, you hide the EV and tell the electrician you want a 30A general purpose circuit in the garage, for welders, compressors, kiln, and other stuff. And get a 14-30 socket there. If you "occasionally" plug in an EVSE, good on you.

An EVSE on 30A will plan to draw 5.76KW, and dryers are assumed to be 5.5 KW.

A 30A socket will give 150-180 miles a 10-hour night... and like Alec says elsewhere in that video, it's all you'll ever need.

I have NOT discussed a service upgrade.

Because you probably won't need it if you listen to the above.

Now, what about "circuit breaker spaces"? For that, you'll either need to use tandems (if an option in your panel) or install a subpanel and move some of your circuits to there to make room for the subpanel feed breaker.

Now you can't throw another breaker in that outdoor panel. That extra breaker space is for solar only (and used that way, it allows up to 100A of solar - no 120% limit there!) However, you can do a neat trick: you can "TEE" off the bottom (breaker-protected) side of that main breaker to a second 100A panel somewhere else. Since the feeder is protected by a 100A breaker it must be 100A cable. The standard wire for 100A service is #2 aluminum - it's safe, really. Don't waste your money on copper. The subpanel must also be >=100A rated, but you'll want lots of breaker spaces anyway - breaker spaces are cheap. That will not add one single iota of extra capacity to your house, so you will still be current limited at the EVSE, but it solves the "breaker spaces" problem at least.

It also cues you up for if you ever get a service upgrade; you can get a 200A "ranch panel" and fit two 90A breakers to feed existing house panel and new panel independently. (90A = no longer qualifies for 310.15(B)(7).)

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  • You're right - my commute is short enough that a 20amp circuit really would be enough for one EV. It'd probably even work if/when my wife gets an EV down the road under most circumstances. My city follows the 2017 NEC and using the load calc spreadsheet they provide, a 20amp circuit would have my calculated demand load at just under 100amps. One question - if I go this route and run a sub-panel to garage, 20amp circuit, and hardwire a EVSE (that could charge at 40 or 48amps) but I commission to run on that circuit and limit it's speed, would this pass inspection?
    – RobbyV
    Oct 10, 2022 at 1:48
  • @RobbyV it should but you may need to do some advance education of the inspector. On the subpanel, I urge you to take advantage of an oddity in wire pricing where far and away the cheapest way to get 50A feeder is to use 90A aluminum feeder (#2). At this very large size, aluminum is proven safe. The size of the subpanel itself is disregarded in the load calculation, only the loads matter. When you are ready for two EVs, use Share2 power sharing, which has multiple EVSE's dynamically share a single power allocation based on the EVs' needs. Oct 11, 2022 at 4:05
  • I will suggest that to my electrician. Here's a question: if I already had 200amp service line and I installed a ranch panel, would I need to do anything to my existing 100amp panel in my basement (or the line to it) if I added a 2nd 100amp panel in the garage? Then I can utilize 100amp in both the house and garage for a total of 200amp. I ask b/c I know my city underwent a project some years back of burying electric lines. There could be a chance that they fed the house with a 200amp line. I would need to check with the city, of course.
    – RobbyV
    Oct 11, 2022 at 14:27
  • I did confirm from my city that my service line is for 200A.
    – RobbyV
    Oct 12, 2022 at 17:54
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I doubt that your meter panel will support an additional 240 volt breaker. Those additional slots are probably for a larger type of main breaker. There are meter panels that have additional slots but they are in a user friendly part of the meter panel. Your panel is sealed by the power company so no user friendly breakers would be in there. Depending on your type of panel, you might be able to get a few tandem breakers. Those are two breakers in the space off one. That could free up two slots in your panel.

A 100 amp service is going to be stretching it. Are you appliances electric with the exception of the furnace,which still as a blower? If this job needs an inspection, the inspector could require an increase in service.

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  • Tandem breakers are an interesting option I wasn't aware of. The furnace, hot water heater, dryer, and stove are all gas.
    – RobbyV
    Oct 8, 2022 at 14:49
  • @RobbyV -- if you get us photos of your panel, including the label on the inside of the door, we can tell you what your options are for squeezing more in, or what the best path for upgrading is, for that matter Oct 9, 2022 at 15:40
  • @ThreePhaseEel I've edited the original post to add a link to images of my panel
    – RobbyV
    Oct 10, 2022 at 1:02

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