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I want to figure out how to hardwire an EVSE directly into a sub-panel. I already have the EVSE (ClipperCreek HCS-40, 30A charging current, 40A breaker), it was installed previously in another home with a 14-50 plug (but I think it was meant to be hardwired given the whip).

Our jurisdiction currently lets me use the 2017 or 2020 NEC. I understand that I need a GFCI breaker if I use a 14-50 outlet for the EVSE, but not if I hardwire it. The unit comes with a 3 ft whip, which appears to be PVC coated MC cable. It has 2 hots and a ground in the whip. All are 10 gauge. I want to mount the EVSE right next to the panel. If I run the whip into the panel, I do not see how I can land the #10 wires on a 40A breaker. I would rather not add a box with a bunch of Polaris connectors to transition from the #10 to #8 THHN wires.

I opened up the EVSE and it looks like I could run new #8 wires to the contactor and ground bar, and then use some LFNC from the EVSE to the panel (see picture of the inside of the EVSE below). Is this acceptable, or is that considered modifying the equipment? I've seen other hardwired EVSE's where you terminate the wires inside the EVSE. I've received some very helpful suggestions in response to another question I asked related to adding the load to my panel.

What is the most direct way to hardwire this EVSE into a panel? If I use the existing whip, what type of connector should I use on the PVC coated MC?

There is a lot of debate on how this could actually be a 30A unit, since the new HCS-40 are 32A (which makes sense given that this is the max continuous load you can have with a 40A service). To test this out, I temporarily wired the EVSE into a spare breaker and set the car to charge.

Below are a screenshot from the Tesla app, a picture of my clamp meter and a screenshot from recordings from my WattNode with 2 50A CT's. I think this proves that it really does not want to give me more than 30A. For those of you unfamiliar with the Tesla app, the fact that it says 30/30 shows that this is the max will draw from this EVSE.

EVSE next to panelPanel with EVSE whipEVSE InteriorConnectors on EVSEEVSE nameplate Screenshot from Tesla app Picture of clamp meter showing 29.8A WattNode monitoring screenshot

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  • any changes inside the box, is considered changing the equipment, void the warranty.
    – Traveler
    Commented Nov 27, 2022 at 2:41
  • Are you saying the cable is not long enough to reach the 40A breaker ?
    – Traveler
    Commented Nov 27, 2022 at 2:47
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    The cable is long enough, but it would be a #10 wire on a 40A breaker. The QO breaker is listed for "AWG 8...AWG 2 copper or aluminum" Commented Nov 27, 2022 at 2:52
  • @Ruskes, I'm not worried about the warranty (EVSE is old), but I want it to pass inspection. Commented Nov 27, 2022 at 2:53

2 Answers 2

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I already have the EVSE (ClipperCreek HCS-40, 30A charging current, 40A breaker)

Well. I see where it says that on the label, but just this week I talked to ClipperCreek on that exact question (32 vs 30) on your exact unit (HCS-40) and they said it was definitely 32A, and in a cheeky way like "of course we fully exploit the 40A circuit, do you even need to ask?"

(EVSE's are a continuous load per NEC 625.42, and get a 125% derate. 32A x 125% = 40A on the button, fitting hand and glove to a 40A breaker.)

A pointless distinction, since a 30A EVSE still needs a 37.5A wire and circuit.

it was installed previously in another home with a 14-50 plug (but I think it was meant to be hardwired given the whip).

The HCS-40 is approved either way.

Our jurisdiction currently lets me use the 2017 or 2020 NEC. I understand that I need a GFCI breaker if I use a 14-50 outlet for the EVSE, but not if I hardwire it.

Correct. The EVSE is a smart GFCI and nothing else but a tone generator making a 1000 Hz square wave at 53% duty cycle. The square wave tells the car "you may draw 32A from this port". That is how charge rate control is done with EVs.

The "smart GFCI" does a few things. It self-resets a number of times, so that nuisance trips don't prevent charging. Connected ones can signal you that charging is failing. It will connect and disconnect at the car's request. Some models sense DC ground faults (which blind a regular GFCI). The upshot is a plain GFCI on an EVSE is wasted.

It has 2 hots and a ground in the whip. All are 10 gauge

Follow the bouncing ball. That is legal because it is part of the equipment and as such is under the jurisdiction of ETL (Intertek Group plc). Similarly, smart switches may come with 16 AWG pigtails. It's not governed by NEC, and ETL says it's OK because of the particular use of the cable.

You can use that according to the instructions. NEC 110.3 requires you follow the instructions. This requires you read them lol. ETL approved the instructions as part of approving the equipment.

If I run the whip into the panel, I do not see how I can land the #10 wires on a 40A breaker. I would rather not add a box with a bunch of Polaris connectors to transition from the #10 to #8 THHN wires.

That would be a simple matter if your panel was surface mount. Unfortunately, it is flush mount and I don't think the instructions say anything about plunging it into the innards of a wall and then burying it in insulation and drywall mud.

You're making too much out of the surface mount box (a 99 cent drawn steel 4x4 box will suffice) and Polaris connectors (honestly? Tan wire nuts will suffice.)

Just come out the bottom of the panel with 8/2 Romex and into the back of the surface mount box. Hardest thing will be finding two cable clamps fit for 8/2.

I opened up the EVSE and it looks like I could run new #8 wires to the contactor and ground bar, and then use some LFNC from the EVSE to the panel (see picture of the inside of the EVSE below). Is this acceptable, or is that considered modifying the equipment?

We're the wrong people to ask. All approved uses are listed by ETL - guess where - in the instructions.

What is the most direct way to hardwire this EVSE into a panel? If I use the existing whip, what type of connector should I use on the PVC coated MC?

Since your panel is flush-mount you have no choice but to run some wire inside a wall. I would run 50A wire honestly, right into the back of a surface mount 99 cent corner-screw drawn steel 4x4 junction box.

Run the wire whip into one of the side knockouts - it has the fitting for that already on it. 10-32 ground screw, blank lid and a couple of tan wirenuts and you're done.

This will also allow for quick change-out of the EVSE should that be necessary, and for that matter, a 14-50 receptacle could be installed in the 4x4 box if you find yourself in a jam or simply have a friend with an RV visit. Hence my advice for 50A cable - you're only going 2 feet lol.

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  • I added some pictures/screenshots above, showing that the unit is really only putting 30A out. I will add a surface mounted box to transition into the wall. Commented Nov 29, 2022 at 0:01
  • @ChristianK sounds like ClipperCreek misled me then. Well geez, if they're product is on gen2 and they went to UL again for another cert, why didn't they add the select-an-ampacity? Houses often can't support an additional hard 30/32A (calculated 37.5/40A) load on their service Load Calculation, and people often don't find that out until after they bought the EVSE. Commented Nov 29, 2022 at 0:18
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A quick search says 10 AWG is OK for 30A NM, 35A THWN 75 C and 40A THWN 90 C. Typical equipment and breakers, as I understand it, are rated 75 C and not 90 C. So that would indicate a max. of 35A. The wire, in general, needs to match the breaker (i.e., the 40A of the breaker, not the 30A of maximum continuous usage), so 10 AWG doesn't normally qualify for installing this equipment. However, if this whip with 10 AWG wires came factory installed then ETL approved installation that way and it is OK. Assuming that's the case, you can either:

  • Install a junction box to transition from 10 AWG to 8 AWG for the breaker.

or

  • Attach the whip to the panel directly with an appropriate clamp and transition from 10 AWG to 8 AWG inside the panel.

10 AWG to 8 AWG does not require Polaris or other expensive connectors. According to the Ideal catalog, you can use:

  • 342 Gray
  • 454 Blue
  • BT2 Red

Some other sizes (e.g., 341 Tan) will likely work, but Ideal doesn't publish every possible combination/permutation of wire sizes.

Of course, you might need to be get a large package, but the per-wire-nut price is very low.

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  • Read the OEM label.
    – Traveler
    Commented Nov 27, 2022 at 4:24
  • No. 10 AWG is limited to 30A per 240.4(D). Also, this is NOT a 30A charger, OP is giving misinformation there. Charge rate is 32A actual and 125% continuous-load derate does apply. Commented Nov 27, 2022 at 4:44
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    I think it's an error. ClipperCreek says it's 32A. Maybe a software push? When SAE was first promoting J1772, they made a lot of Powerpoint decks that showed duty cycle percentages of 10%, 20%, 30%, 40%, 50% corresponding to 6, 12, 18, 24 and 30A. Things like that tend to get a life of their own, and I think somebody perhaps at UL went "Oh, those are the only allowable charge rates". I'm sure they've wised up by now. Re: the whip, I think UL is figuring on air cooling, intending the whip to go into a box. And not dive into a wall where it cannot cool. Commented Nov 27, 2022 at 6:18
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    I mean at the time, the very idea that charge rate could be variable and software-directed was blowing a lot of people's minds. This is not your father's battery charger. Remember GM's previous charger was an inductive paddle! Commented Nov 27, 2022 at 6:23
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    Most EVSE will charge based on a setting you select. That can be either done via the car or via some setting (buttons, switches or some "App" interface, depending on the EVSE) directly in the EVSE. Even if set to full (=30 or 32) you may find that at various points the actual current flow will be lower. It doesn't matter for purposes of this question. The factory-installed 10 AWG wires are, by definition, OK. And your wires (whether a short extension in the breaker panel or 50 feet through the house to the garage, etc.) have to be 8 AWG (because 30A=10 AWG is for total, not continuous) Commented Nov 27, 2022 at 17:56

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