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I had an electrician come and install a NEMA 14-50 outlet (on a 40A GFCI breaker) for an EV charger. I have the 32A charger that plugs into it, but it is also plugged into a 30 ft 50Amp RV extension cord. I noticed that after about an hour or an hour and a half, the breaker inevitably trips.

Most of the time when I reset the breaker (usually a while after it trips), it resets just fine. I have noticed that the couple times that I've tried to reset the breaker right after it trips, the breaker won't reset, it will click back into tripped mode (even if I unplug the extension cord and charger so it's just the outlet on the circuit). I felt the breaker today when this happened and noticed it felt warm to the touch.

I had the electrician who installed it come out a few weeks ago to check it. He did some multimetering and didn't detect any issues. When I plugged in the car, it charged like it always did (but of course, he couldn't wait around for 1.5 hrs before it tripped).

I did notice that the EV charger that I have says it has built in GFCI protection and I have seen other EV chargers with GFCI protection say there may be nuisance trips when a GFCI charger is put onto an outlet with a GFCI breaker.

Does anyone know if this is the issue or there is some other issue consider? Should I just replace the GFCI breaker with a non GFCI version since the charger already has ground fault protection, or is it a bad breaker or something else making it heat up?

TLDR summary: 40A GFCI breaker powering GFCI EV charger always trips after 1-1.5 hours after charging EV at 32 Amps. Should I replace GFCI breaker with non-GFCI version?

Update: Took apart receptacle and was able to tighten all the screw heads holding the 4 wires in (by about 1/2 turn). Then opened up the panel and tried to tighten the screws holding the wires into the breaker and noticed that the screw holding the black wire is somehow stripped (or the hole is stripped) so that there is no tight position, it just spins forever. This could be the problem? I'll have the electrician come out and check it again and have them fix it.

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    Since the breaker is refusing to reset right after tripping, even with nothing plugged in, it’s not a GFCI trip.
    – DoxyLover
    May 29, 2023 at 7:09
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    Does the breaker run warm when the charger isn't running? May 29, 2023 at 11:27
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    @DoxyLover It could be a ground fault in the wiring or receptacle box itself. The classic neutral touching ground, for instance, somehow caused by thermal expansion induced movement.
    – Ecnerwal
    May 29, 2023 at 13:08
  • Thanks, that is good to know. I think maybe I'll take apart the receptacle box and see if the outlet is wired correctly without any chance of something touching with some expansion. May 29, 2023 at 20:56
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    You update tellingly mentions tightening but not using a torque driver to do so. That is a required thing for properly tightening terminal screws to prevent problems that come from too tight as well as too loose.
    – Ecnerwal
    May 30, 2023 at 2:08

4 Answers 4

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I will be calling the "charger thing" an EVSE. Bear with me. Its job is to tell the car how much current to safely draw, and be a disconnect, and be a GFCI. The actual battery charger is custom matched to the battery and is onboard the car. It's quite large, and obeys the "how much current" signal.

My guess is, it's the socket

I'm not particularly concerned with the socket getting warm - they're going to get warm. But there have been lots of proplems with the socket getting hot. On the "cheap end" ($12) of the spectrum, these sockets are intended for ranges, where they get plugged in once every 20 years and whose load is very intermittent (since each heating element cycles on and off thermostatically). On the high end ($90) they are made for RV parks where they will get plugged/unplugged 3 times a week.

We have a lot of reports of socket damage or burn-ups when cheapie sockets are used for continuous EV loading. And my guess is, with that extension cord, you're doing plug/unplug a lot.

enter image description here

And a test you can do here, if your car gives you a "soft" way to limit amps, is tell the car to take 16 amps. *

Or is it really pulling 32A?

Scuttlebutt is that those "travel EVSEs" draw 32A. That's reasonable because of the above: There is no 40A receptacle (there is a finite number of pin arrangments and NEMA has a lot of types)... so 40A circuits use NEMA 14-50. Continuous EVSE loads must draw 80% of circuit rating, so a NEMA 14-50 dongle plug* should assume 40A circuit and ask for 32A. But wait... watch this bit of a video (at 26:18) of correct use of that EVSE, and 1 minute in at 27:18 it's pulling 40A. So the idea of 32A may be "notional".

What would pulling 40A continuously on a 40A breaker do? Let's look at the trip curve

enter image description here

How do you read that? That is a log-log graph - each scale is logarithmic; each major division is 10x the last. Left is "won't trip", right is "will trip" and gray is "might trip". At 2x overload, trip happens between 9 and 35 seconds.

Well, what happens at 100% "over"load? That indicates trip between 400 seconds and never. Realistically "1.5 hours" is conistent with that; that's why continuous loads require 125% derate (so 32A needs 40A).

So check your car's indication and see what amps it's actually drawing. If it's 40A, that's your trip cause, and that is not a defect. You need a different EVSE that'll tell the car 32A.

* Would 16A even work?

At level 2, 16A is actually plenty for almost anyone who would seriously consider an EV. Even with Technology Connections' very conservative figures, to allow for winter, larger EVs and stuff... that's 100 miles a night. Realistically much more in most cases. And I'm sure you've left the house in the morning with less than a full tank of gas, so even after a long EV day, you don't need to be back to 100% the very next morning. Their treatise on capacity is here.

How do you get 16A out of an EVSE? For casual testing, you can just use any soft controls your car has. If it's for a hardwired installation it must use a UL listed method. With travel-unit EVSEs with exchangeable dongles, see if your manufacturer makes a NEMA 6-20 plug for it - the current signal comes from a microchip inside the plug, and that will say "16A". With wall-unit EVSEs, most are configurable via a UL-approved method.

The extension cord, though.

NEC 110.3(B) requires you install equipment according to labeling and instructions. Your travel EVSE's instructions forbid extension cords, and your electrician darn well knew it. (you, I can forgive). The electrician's job was to school you, and insist on installing the socket where the car will be. Or better, up-recommending you into a hardwired wall-unit EVSE, but that requires specialty EV charging knowledge most electricians do not have, so I can't fault them there.

So yes, either cars should be moved around as needed, or the outlet should be moved, or...

A "wall unit" style EVSE is really the more reliable and versatile way to go. Because that does not require a plug and socket. That can be hard-wired in, which means, plug and socket woes go away, but that's not all. The EVSE itself has GFCI capability inside it, so if the unit is hard-wired, it becomes a GFCI "receptacle". As you might know from the 120V kind, if you have a GFCI receptacle you don't need a GFCI breaker.

So the ideal solution is to extend the wired circuit to a practical charge location, place a hardwired EVSE there, and dump the socket and the "dumb GFCI" breaker. The EVSE's GFCI is "smart" - UL authorizes the unit to self-reset at intervals, as many ground faults will clear themselves over time. Also the EVSE does not lose power when its internal GFCI trips, so if it has internet abilities, it can signal you that something is wrong, so at least you can get level 1 charging going.

Note that most wall-unit EVSEs have DIP switches or other UL-approved setup procedure to be hard-coded for any circuit size, so a "nominally 60A breaker" EVSE can be set for 40A breaker and run 32A actual. (not to be confused with a car's "soft setting" to slow charging at the driver seat or the app. That's not enough for a UL listing.) It's simply sending a different code to the car in each case. They also make wall-units which coordinate with each other so multiple EVs don't exceed a fixed allotment (nice for your 2nd EV), and they make wall-units which clamp your service wires and will slow EV charging to prevent service overload.

But like I say, that's EV specialty knowledge - and most electrians don't have it, and even if they did most consumers would resist such a radical departure from their own idea. It would be perceived as a huge "up-sell".


* On those travel unit EVSEs with swappable dongle plugs, the plug contains a microchip that tells the EV how many amps the plug is. That's what the 4th pin is for (it's not neutral; EVs don't use neutral in 120/240V supply).

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  • So for a value EV installation, what breaker and what cable? Would aluminum conductor be a reasonable choice? If aluminum cable is used what connectors to the EVSE? May 30, 2023 at 23:12
  • @Jim it's complicated, depending on the "value" you're chasing. If the priority is to use the supplied "travel unit" EVSE and avoid buying a wall unit, and they don't make inexpensive 20-30A dongles for it, a 50A circuit (yes #6AL) might be the cheapest. If a wall unit (virtually none accept AL wire, c'mon guys), then you make a call between "Cu the entire run" and "install a disconnect solely because its lugs accept Cu and Al, run the last 2 feet in copper". May 30, 2023 at 23:19
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There's multiple questions here, and I'm only taking on one.

Should I just replace the GFCI breaker with a non GFCI version since the charger already has ground fault protection, or is it a bad breaker or something else making it heat up?

Not if you're interested in the install being to code. You will need a hardwired EVSE in order to run it without a GFCI.

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  • Feel free to provide a code citation if you have one. To my understanding it's required since revisions to the 2017 code, and fully in the text of the 2020 code.
    – KMJ
    May 30, 2023 at 22:27
  • How exactly is a hard wired connection to an EVSE made? May 31, 2023 at 22:33
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    You connect a conduit to the EVSE, then run wires directly from the panel in to the EVSE. That way you don't need a GFCI, a plug, an outlet, etc.
    – KMJ
    May 31, 2023 at 22:39
  • The cable from the breaker goes into a box, presumably resessed. Does the EVSE fit over the box and act as the cover or is there a separate cover with a hole for a cable or cord to the EVSE? May 31, 2023 at 22:42
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    All depends on the EVSE. Look at the Tesla installation manual for some pictures of common ways to install.
    – KMJ
    May 31, 2023 at 22:46
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If you think the breaker might be overheating, you should try lowering the charge limit from 32A to something like 20-25A and see if that stops the problem. If it does, then you'd need to look into why it's overheating on a load it should handle (poor connection - damaged bus in the circuit breaker panel? Defective breaker?) If not, you could try going even lower - especially if the time to fail increased when you lowered the current the first time. If the time to fail remains the same at lower currents, this might not be it. Then again, merely warm is not necessarily a problem. But read on.

If it's developing an actual ground fault, that would have to be between the breaker and the receptacle since it persists without the cord plugged in. Something a bit too close clearance that touches when the circuit gets warm from use...that should also take longer to fail, or not fail at lower currents.

If you are comfortable working with the panel open, you could verify or rule out the "defective breaker" hypothesis by waiting for it to fail and quickly disconnecting the wires from the breaker before attempting to reset it. If it won't reset with no wires attached, it's definitely a breaker problem. If it will, it's a wiring problem.

The use of a receptacle requires the GFCI breaker.

If you want to take advantage of the EVSE's self-resetting GFCI, you need to hard-wire the EVSE, not plug it in. Presumably you can't do that without a lot of digging (or other circuit relocation work you've chosen not to do) if you are using it with a long extension cord now.

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  • And OP remember, the easy way to disconnect wires from a breaker is to rock the breaker off the panel, hold it in your hand and unscrew the wires. Then snap the breaker back in. It's totally legit to pop the breaker off before unhooking the wires from it. Also the wires will be on VERY HARD beause your pro used a torque screwdriver. May 29, 2023 at 18:20
  • The electrician who came out did rewire the breaker so I think that's probably not the issue. but he didn't open the receptacle so maybe I'll check that to see if there's any issue that could happen after an hour of charging. Unfortunately, my car charger doesn't allow for changing the charging level, It's 32A for level 2. The car does let you change the 120V amperage but not for L2. May 29, 2023 at 20:59
  • added update to the main question where I note that the screw holding the wire to the breaker is stripped and not able to be tightened (spins forever) May 30, 2023 at 2:01
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IMHO it sounds like the breaker is undersized, and overheating. I have a Nissan Leaf, and although the plug with built-in protection systems clearly says (30A) on it, the owner's manual says it requires a 50A circuit.

Also, you can select charge speed from within the vehicle, and the slower you charge, the longer the battery lasts and the less the breaker would heat up.

The first thing I would do is check the owner's manual. I would also consider setting the vehicle to the slowest possible charge speed and see if that changes anything.

Edit: Also, note that every time a breaker trips, it weakens the breaker. So, even if you find the problem now (like possibly that loose screw you updated about) the breaker may continue to trip because it's been weakened by tripping so many times.

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