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My garage has an existing NEMA 14-50 outlet connected to the breaker box via EMT conduit. The conduit only has 2 hot wires and 1 neutral (all #6 THHN), with ground being provided to the metal box via the conduit itself (the conduit is bonded to the breaker box).

enter image description here

I now want to replace this metal box and NEMA outlet with a Tesla EV charger, but I'm torn about how to properly ground it. The Tesla charger comes in a plastic box that can't be directly grounded via the conduit; instead, it expects a ground wire to be explicitly connected.

Tesla charger box

One easy way I can think of is keeping the existing metal box as a junction box and using it to feed the Tesla charger below it. In the junction box I'd add splices for the 2 hot #6 THHN wires + a new #10 THHN copper ground conductor bonded to the junction box itself. While I think this would work (but let me know if it won't), it's not ideal because:

  1. I'd need to keep 2 boxes (junction box + Tesla charger) instead of 1 which won't look as good.
  2. The Tesla charger will be lower on the wall than I want.
  3. I'm less familiar with EMT so would likely use PVC conduit between the junction box and Tesla charger, and I don't think this mix would look good (EMT --> metal box --> PVC --> Tesla charger).

Are there other approaches to make this work without looking bad?

Note that the conduit is really long and curvy, so it's not practical to try and feed another conductor through it all the way to the breaker box.


Update(2023-01-17): I've completed this project with a few changes from my original question, and posting these here for the benefit of future readers.

  1. Position: When I started work, I realized that a) the current box is too high to comfortably host a Tesla charger and b) even if we kept the height, there isn't enough wire slack to loop them the way the Tesla charger expects.

    As a result, I needed to either keep the box as a junction box and splice some new wire to cover the distance, or purchase and fish 30' of three #6/#10 AWG conductors (or 4, if I want to future-proof it with a neutral). Obviously the latter would cost a lot more time and money, so I went with keeping a j-box.

  2. I initially planned to grab the ground from the final piece of EMT using a grounding bushing, but my Home Depot only had these in 2" (I needed 3/4"). So I hooked up a ring terminal to my #10 AWG green THHN, screwed that into my j-box, and ran it through the new conduit to the Tesla charger.

  3. I took Harper's advice and took this opportunity to learn how to work with EMT. I'm glad I did! It was easier to cut than I expected, and the fittings generally made life easy.

Here's what the final product looked like:

enter image description here

enter image description here

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  • I'm sure one of the electricians will be along shortly with the proper terminology, but I'm 99.99% certain that there are grounding clips that can be attached to the EMT you have to carry the ground from the conduit into a wire that can then be attached to the ground screw in the plastic box.
    – FreeMan
    Jan 13, 2023 at 18:57
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    Jinx, @crip659!
    – FreeMan
    Jan 13, 2023 at 18:58
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    @FreeMan Just need an EMT master to show the right part/name.
    – crip659
    Jan 13, 2023 at 19:00
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    I think an inspector would accept a bonding bushing duckduckgo.com/… Jan 13, 2023 at 20:12
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    Where the conduit enters a plastic enclosure you could thread the bushing onto the conduit connector, then a #10 bare or green jumper from bushing to ground terminal. Jan 14, 2023 at 2:07

3 Answers 3

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Ordinary EMT connector to a bonding bushing.

The basic common EMT connector you might use to go into a standard knockout (heck, you have one right on that existing box). I prefer the compression type especially if you might need to spin it in close quarters.

enter image description here

That connector has a thread on it, right? Enter the Tesla enclosure and screw a bonding bushing into it. Or if clearance requires, screw the connector into a bonding bushing! (remember what I said about "easier to spin").

enter image description here

If the Tesla has a 1/2" knockout you can go right into that. If it has a larger KO then you use a "conduit reducing washer".

enter image description here

Given the small quantity you need, consider a family owned hardware store (such as an ACE or HWI affiliate). They're likely to be more happy to sell you single parts at sane cost instead of making you buy a bag of 10 like the big-box stores do. I know my local "boutique" hardware store does. For the more obscure stuff, an electrical supply house.

Other thoughts

Most people think they need much more charging power than they really do. Here is a sanity check and good primer on the subject. If ya got it flaunt it, but if you don't got it, don't set your panel on fire flaunting it. OK?

Save your old hardware. Before you sell your house, roll it back to plug and socket. People make better offers on houses that are obviously set up for EV charging, and "14-50 socket" has more curb appeal than "empty hole were EVSE was".

Also, consider multiple EVs. Now, a large circuit can let 2 or even 4 EVs share a single current allocation dynamically. When you have multiple cars, a funny thing happens. It's exceedingly rare for them all to need a big charge. You'll have 3 cars, one needs 15 miles, one needs 30 miles and the other needs 180 miles. A 40A circuit will do all 3 cars in 11 hours dynamically on the fly, no clock watching, no swapping cords. Really.

6 AWG copper is 65A wire. Due to technicalities and Tesla not bothering to read NEC before designing their units, you must use no larger than the 60A setting when commissioning the EVSE.

Even if you didn't before, do a NEC Article 220 Load Calculation on your house's service excluding the EVSE. This is a Code requirement for additional loads. Take your service/main breaker size minus your Load Calculation and that gives you the headroom on your service. Round down to the next 5A increment and use that breaker size when commissioning the Tesla Wall Connector. Most people ignore this altogether and try to set their panel on fire. Insurance won't pay when you do that.

If you're really in a jam and just don't have the service to support the charge rate you'd really like, it's possible to use "load shedding" to solve this. Use a contactor or EVSE feature to have the EVSE interrupt (or simply slow) when other loads are running. The best EVSEs install a current transformer on your service wires so they dynamically change as loads come on/off.

I'm less familiar with EMT so would likely use PVC conduit

You'd be better off seizing the learning opportunity and learning about EMT. It really is marvelous stuff, doesn't cost any more than PVC, performs better, and best of all, errors are cheap since everything unfastens. The most you'll ever waste is a little bit of stick. Unlike PVC which must be glued.

Note that the conduit is really long and curvy, so it's not practical to try and feed another conductor through it all the way to the breaker box.

Another thing worth skilling up. Not that hard, the trick is, pull out all the wires and use them to pull in a stout pulling string, then rearrange the wires and pull it all back in. Make full use of any "pulling points" between here and there. If one of the "pulling points" is a junction box, you can grab ground at that intermediate box and don't have to go back to the main panel.

If there is somewhere unobtrusive yet accessible along the EMT run, you can pull the wires back beyond that point, and insert a common 4x4 steel junction box there (about a buck) with two EMT connectors, and then grab your ground at that box.

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  • I'm pretty sure Tesla went with 60A because code starts requiring a disconnect once you cross that line. EVSEs on a 60A or smaller circuit don't need a local disconnect. Peek at 625.43 for that. (also a while ago they stopped putting 72A chargers in their cars and went to 48A only so it no longer matters)
    – KMJ
    Jan 14, 2023 at 6:49
  • Good point, it's an opportunity to learn about EMT. One basic question: why are so many of the EMT fittings for 1/2" (in this post but also in a search on homedepot.com)? Is 3/4" EMT not as common? The Tesla charger has 3/4" knockout so I'd need a couple of reducing washers if my conduit is also 1/2".
    – peter
    Jan 14, 2023 at 17:16
  • @peter your conduit looks like 1/2". I never had any trouble finding 3/4" everything. Mind you I shop a lot at family owned lumberyards and electrical supply, the box stores can be pretty flaky about carrying "less popular" items. They'll have a proprietary surface conduit wiring system like Wiremold, and they'll sell the left hand corners but not the right hand corners (mirror image) because they fell below some sales threshold in the computer. Maddening. Jan 14, 2023 at 23:18
  • @KMJ I'm not surprised. Larger onboard chargers cost money, add weight, and weight requires more battery for the same range so more money still. And 20-30A is plenty for home charging. 60A is for "destination charging" e.g. plan your trip to arrive at the hotel with 7% remaining and want 100% by morning. Jan 15, 2023 at 3:30
  • Even 32A is fine for destination charging. A Model Y arriving at 5% will charge to 100% in ten hours from a 32A charger, give or take.
    – KMJ
    Jan 15, 2023 at 3:32
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One 'nearly right' approach would be to use the existing three wires you have in a new fashion, i.e. to remark the neutral as a ground and move it to the ground bus in the panel. You already have three wires in the conduit, after all, and the EVSE doesn't need the neutral as there's no pin for it on a J1772 plug anyway. Code talks about it this way:

250.119(A) Conductors Larger Than 6 AWG. Equipment grounding conductors larger than 6 AWG shall comply with 250.l19(A)(l) and (A)(2).

(1) An insulated or covered conductor larger than 6 AWG shall be permitted, at the time of installation, to be permanently identified as an equipment grounding conductor at each end and at every point where the conductor

Exception: Conductors larger than 6 AWG shall not be required to be marked in conduit bodies that contain no splices or unused hubs.

(2) Identification shall encircle the conductor and shall be accomplished by one of the following:

a. Stripping the insulation or covering from the entire exposed length b. Coloring the insulation or covering green at the termination c. Marking the insulation or covering with green tape or green adhesive labels at the termination

As this wire is 6 AWG you can't remark it and still be code compliant, but it's not something I would lose sleep over if you decided to bend code in that fashion. The totally right way would be to pull a new green or bare wire for the ground, and you could do it using the white wire as a fish tape to avoid having to upsize the conduit. Assuming the conduit was installed to code regarding room and bends, it's going to be straightforward to pull a replacement for the white wire.

Absent that, my local electrical supply house will happily sell you a conduit ground clamp for about $2. You'll still need a J-box though as you will need to get that ground wire in to the equipment some how. It's probably easier to leave a J-box in place and just add a ground wire from the EVSE back to the J-box, where you attach it with a screw.

Personally though I'd pull a new green wire in place of the white. It'll look cleaner, and you get to live with this install for a long time.

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  • > Absent that, my local electrical supply house will happily sell you a conduit ground clamp for about $2. You'll still need a J-box though as you will need to get that ground wire in to the equipment some how. It's probably easier to leave a J-box in place and just add a ground wire from the EVSE back to the J-box, where you attach it with a screw. Do they make any conduit ground clamps that can work from the inside of the EMT? If so, can I just terminate the EMT at the plastic Tesla charger and hook up its ground cable to the device? I am trying to avoid having an explicit j-box there
    – peter
    Jan 13, 2023 at 20:53
  • Also just trying to understand -- are you saying you're only allowed to re-identify the edges (e.g. by stripping insulation) if the wire was larger than 6 AWG, but not 6 AWG itself? I'm curious why that is..
    – peter
    Jan 13, 2023 at 20:55
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    @peter I think it is because the really big stuff is not so common. In a typical house, it will only be for the main panel feed and possibly subpanel feeds. With very rare (and probably not a great idea for other reasons) exceptions for on demand water heaters or EV charging (at a beyond typical rate). So fewer people have to deal with the really big wires, and almost always in the context of a feeder and not "ordinary" wiring. Jan 13, 2023 at 21:04
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    Can't re-mark neutral as ground unless it is #4 or larger. Jan 14, 2023 at 5:10
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    @peter turns out my local electrical supply does have them. Appleton makes them all the way down to 1/2 inch. In stock at my local Platt. Check your local electrical supply, it seems likely they well have them (though my local Ferguson does not). About $9 each.
    – KMJ
    Jan 18, 2023 at 0:55
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You can't remark any wire as ground except by either stripping all the insulation or taping the entire length (except an inch on each end) with green tape. You have two options:

  • Add a ground wire

You have conduit. There should be plenty of room to add a ground wire. Snaking it the whole way to the panel might be trivial or might involve pulling through several different sections.

  • Leave the metal box in place

Remove the receptacle. Replace the cover with a blank plate. Route a short set of wires (various methods available, but basically a tiny bit of conduit) from the Tesla box to this box. Connect black and red to black and red. Cap the existing white wire. Connect a green wire from the Tesla box to a ground screw like this one:

Ground screw

First link on Amazon is for a 100-pack. You can get smaller packs at a hardware store or big box store. Doesn't have to be green, just has to be the right size and fine threads.

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