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).
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.
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:
- I'd need to keep 2 boxes (junction box + Tesla charger) instead of 1 which won't look as good.
- The Tesla charger will be lower on the wall than I want.
- 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.
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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.
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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.
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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:
Best Answer
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.
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").
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".
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.
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.
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.