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I want to install a 40A electric vehicle charger (probably a ClipperCreek HCS-50) in my unfinished attached garage in the Puget Sound area of Washington State. I intend to have this inspected and permitted, but it's been a good learning experience in a variety of ways already.

I haven't installed a branch circuit before, but this seems about as dirt-simple as it could get: the location I'd like to put the EVSE is about 20 feet away from my service panel, which has open slots on it and sufficient extra capacity in the 200A mains breaker.

To do the install, I've purchased 25 feet of 6/3 NM-B (ampacity 55A) and a 240V 50A breaker that matches my panel brand. I will run the 6/3 along the same path of already drilled holes in the exposed studs to the point where I'll put a NEMA 6-50 receptacle.

  • I'm not clear on whether it's necessary to have a bushing on the entrance to the box where the receptacle will go, but intend to add one to err on the side of caution.
  • I believe the routing through the studs means that I shouldn't need any further protection from physical damage. I think the hole bored through the stud counts as supports, but the cable will still need to be secured within 12" of each end. I'm not sure how proscriptive this is, but I'd like to use screw-in cable guides similar to this:

cable clamp sample image

  • The path of the cable is near EPS insulation, but there's only one cable there now, so 310.15(B)(3)(a)'s adjustments shouldn't apply.
  • It's indoors, it's a dry location, so normal NM-B is sufficient.

Are there any major obstacles I haven't accounted for, or any likely gotchas that I'll hit during an inspection?

This is similar to the question Questions regarding my plan for new 50A circuit (with pictures), but I believe it's sufficiently different to merit its own question.

  • By unfinished, do you mean no sheetrock at all? Just bare studs? – JPhi1618 Aug 23 at 15:47
  • Yep, just bare studs between the panel and where the receptacle will go. – William - Rem Aug 23 at 16:17
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    If you're under NEC2017, you may consider making the breaker a GFCI or hard-wiring instead of using the receptacle. NEC 625.54 says you need GFCI protection if using a receptacle. – PhilippNagel Aug 23 at 18:01
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    You do need a bushing, the studs are all the support you need but the hole must be 1-1/4” away from the face of the stud if closer than 1-1/4” a nail plate will be required. I would verify that the hole is back and if closer than 1-1/4” put the plates up. In my jurisdiction the open wiring required cover below 8’. 1/2” plywood or Sheetrock is acceptable. + for Phillip on the GFCI requirement if a receptacle. – Ed Beal Aug 23 at 21:03
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    Note for the rest of the folks here: if you're looking in your Codebooks and can't find 625.54, that's because it isn't there -- the NFPA left it out by accident and had to fix that with TIA 70-17-2 – ThreePhaseEel Aug 24 at 0:25
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If it's cord-and-plug, you need a GFCI breaker...

If you are cord-and-plug connecting your EV charger, then you'll need a 50A GFCI breaker instead of the regular breaker as per 2017 NEC 625.54 (as specified in TIA-70-17-2):

625.54 Ground-Fault Circuit-Interrupter Protection for Personnel. All single-phase receptacles installed for the connection of electric vehicle charging that are rated 150 volts to ground or less, and 50 amperes or less shall have ground-fault circuit-interrupter protection for personnel.

...but, leaving the wires nutted off in the box is OK for a hardwired setup

If you intend to hardwire it, though, you can simply terminate the circuit into a junction box with some wire nuts (and a cover if you intend to install it after the final electrical inspection).

As to the rest of the bits...

Getting the cable into the box requires a cable clamp, made of either plastic or metal; this goes into a knockout in the box and holds the cable jacket firmly in place. However, some plastic boxes have integral cable clamps instead of knockouts; with those, you do not need to install a separate clamp.

Attaching the cable to the studs near the endpoints is done using a NM cable staple or strap; these have a somewhat rectangular profile to them to match that of the NM cable itself. (The clip you depict in your photo looks to be intended for low voltage wiring such as coaxial and communications cables; a NM cable will simply be too big to fit into it.)

  • Thanks! The cable clips I have are physically large enough for the #6 cable, but I wasn't sure if low-voltage / data straps would be count, given the "approved and identified" language. – William - Rem Aug 26 at 17:23

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