NEMA 14-50 Charger Tripping 50A GFI Breaker

[MSUcougar]

Had an electrician install a NEMA 14-50 charging setup in my garage in March when I got my 19 M3 LR AWD. Breaker panel is on the opposite wall of the garage from where I wanted the outlet. The previous owner installed a range in the kitchen, and the wire enters the garage at a junction box near where I wanted the NEMA 14-50 outlet, and then runs through a pvc conduit across the garage to the panel. I asked the electrician if it was acceptable to run the wire for the outlet through that existing conduit for simplicity, and that's ultimately what he did. The new outlet is a few feet away from the junction box. I don't know the specific details on type of wire or brand of outlet. So I have a new 50A breaker, and everything has worked fine with no issues for several months until the last couple weeks. The breaker has tripped 3 different times when plugging the car in to start charging. Each time it has worked fine after resetting the breaker. After reading this thread, I called the electrician that installed it and he confirmed I have a GFI breaker (required per code), and how that can cause nuisance trips when used in conjunction with the GFI-protected Tesla cable. He seems to think the tripping is no big deal. He said if it was a loose wire or some other actual problem causing the trip, it would trip every time. The poster from that thread replaced his breaker with a non-GFI one which solved the problem.

Would it be better to have the electrician replace the breaker (with a regular one (against code requirements) or try a new GFI one) or just put up with random nuisance trips? Is there any actual harm/risk associated with the tripping/resetting breaker or is that truly no big deal like the electrician said? It makes my wife a little uneasy and I'm not 100% confident in my reassurances. Looking for a warm fuzzy that the house isn't gonna burn down.

 

[Gauss Guzzler]

There are 3 ways your breaker can trip:

• Over current - Rule this one out as it's almost inconceivable that your 32A charger could be pulling more than 50A without emitting plumes of smoke.
• Over temperature - Very likely cause. There is a thermometer inside the breaker that trips it at a certain temperature and this can easily happen if the screw terminals connecting the breaker to the wiring are not tight enough.
• Ground faults - Unlikely, but not unusual. If something in your house is connecting the ground to neutral it can cause GFCI's on other circuits to trip as they detect voltage on the common ground. Many things can cause this from an improperly bonded subpanel to an incorrectly wired appliance. Another possible cause is poor grounding at your main panel. Any of these issues may be subtle enough to get past a kitchen outlet and may only become detectible when high power is drawn.

There's rumor that Tesla's built-in protection is incompatible with your breaker's GFCI but I strongly doubt Tesla would design such a thing or that UL would approve such a thing. I suspect this belief stems from Tesla's advice against installing wall chargers with GFCI breakers, and is reinforced by the fact that replacing the breaker has resolved the issue for many people.

 

[Rocky_H]

There's rumor that Tesla's built-in protection is incompatible with your breaker's GFCI but I strongly doubt Tesla would design such a thing or that UL would approve such a thing. I suspect this belief stems from Tesla's advice against installing wall chargers with GFCI breakers, and is reinforced by the fact that replacing the breaker has resolved the issue for many people.

I think you are off on the wrong track with this. There is good reason why with either the wall connector or mobile connector, they would very frequently have problems with GFCI breakers, and it's not some misunderstanding or rumor. It's a specific issue with how they are built to operate. The devices check for the ground connection being present and functional. The way they do this is by taking a little bit of current from one of the hot connections and sending it to the ground line to see how it reacts. Is it floating, or does it seem to be tied down to 0V?

Guess what?! That is EXACTLY the behavior that a GFCI system is intended to detect and prevent!! So this ground test is the very thing that will cause GFCI breakers to trip. The only reason this even passes and works most of the time is because of a difference in thresholds that are very close. The charging equipment is supposed to use some very small number of milliamps of current for this test. GFCI breakers are supposed to have some small number of milliamps as a threshold it will allow before it's enough to trip. The Tesla testing amount is supposed to be below that threshold, but they are very close. GFCI breakers and outlets are kind of notorious for that specification being a little off or drifting as they age, so this can become more common, that the EVSE ground test starts setting off the GFCI system.

So this was very annoying that NEC decided to put this requirement into a system that is always going to have problems with it.

 

[Gauss Guzzler]

I find it hard to believe that UL would approve a device that routinely directs power to the ground wire at levels above the human safety threshold of a GFCI. Is there any data or documentation to support this claim?
I've only seen anecdotal evidence from people stating that certain homes seem to be incompatible with GFCI breakers and UMCs, never any proof that the rumored UMC test mode exists, is legal, and is on par with the tripping threshold.

 

[Rocky_H]

I find it hard to believe that UL would approve a device that routinely directs power to the ground wire at levels above the human safety threshold of a GFCI.

Uhhh...huh? It is exactly the OPPOSITE of that. That threshold is much lower than what is required for human safety, because the whole idea of it is to trip long BEFORE it injures someone. It has to have some response time while that current is spiking up, so it is set very low to try to catch it early. So the threshold is so low that normally innocuous tiny levels of current can accidentally trip it.

And again, you are stating something I never said. I never said it "routinely" does that. I said that the UMC's current is supposed to be below that threshold and most of the time is. But GFCI devices are pretty rough holding that specification, so it is still fairly frequent that their threshold degrades lower to where it accidentally crosses over.

Is there any data or documentation to support this claim?

It's a known fact about how GFCI's work--not just a "claim".

I've only seen anecdotal evidence from people stating that certain homes seem to be incompatible with GFCI breakers and UMCs,

*sigh* Then you just haven't seen any of the many threads about it. Frequently it's just the GFCI outlet or breaker being out of spec, even when new. And replacing it with another new one of the same type fixes it, because they can be really touchy.

never any proof that the rumored UMC test mode exists, is legal, and is on par with the tripping threshold.

WTF?! This is hilarious. This is well known that it's how the UMC tests the ground. How else could it test it than by trying to force something onto it and see how it responds? That's the only way it can test it.

 

[ATPMSD]

when used in conjunction with the GFI-protected Tesla cable.

What makes you thing there is a GFI built into the Tesla cable, or did I misunderstand your comment? In any case, the most likely cause is a lose connection, especially as it has worked just fine for months. Check the tighness of all connections at both the breaker box and the plug.

 

[MLXXXp]

What makes you thing there is a GFI built into the Tesla cable

On page 12 of the Mobile Connector - Gen 2 Owner's Manual it talks about a 1 flash fault code indicating "ground fault".

On page 8 of the Gen 3 Wall Connector Manual it talks about the "Integrated ground fault circuit interruption (GFCI)".

 

[ATPMSD]

On page 12 of the Mobile Connector - Gen 2 Owner's Manual it talks about a 1 flash fault code indicating "ground fault".

Yep, you are right. However, a GFI breaker is required for a 14-50 outlet in a garage, so perhaps this has more to do with an internal failure of the MC as opposed to a wiring fault?

On page 8 of the Gen 3 Wall Connector Manual it talks about the "Integrated ground fault circuit interruption (GFCI)".

The Wall Connector does have an integrated GFI, as you noted, and because of this a GFI breaker should not be used.

Have you had a chance to check the tightness of the connections? Any difference?

 

[CoastieM3]

Checking in on this thread. I had a 14-50 with 40A GFCI breaker installed. Attempted charge 4 times and breaker tripped twice. Leaning towards asking them to put a non-GFCI breaker in the box.

From what I’ve read elsewhere, there’s “too much fault detection” between the breaker, the cable, and the car. Thoughts?

 

[CoastieM3]

How do you check charging fault codes?

 

[ATPMSD]

Leaning towards asking them to put a non-GFCI breaker in the box.

Suggest you check to ensure all connectors at the plug and breaker box are tight first. New connections often loosen up as temperatures change with the season. BTW, if the GFI is code an electrician may decline your request.

 

[Gauss Guzzler]

If your breaker is tripping, the problem is most likely at the breaker so you probably won't have any charge fault codes.

You probably have a loose terminal at the breaker, some sort of ground/neutral issue with your house, or a lousy breaker. Changing to a non-GFCI will address all 3 issues, though not exactly in the best way.

 

[CoastieM3]

Suggest you check to ensure all connectors at the plug and breaker box are tight first. New connections often loosen up as temperatures change with the season. BTW, if the GFI is code an electrician may decline your

Everything is tight. The plug was installed 2 weeks ago. The car showed up a week ago. I’m not an electrician but am familiar with basic electricity theory/function. Seems to me that a GFI breaker hooked up to a system with additional GFI protection is likely to trip.

Electrician said he’d swap it out.

 

[MSUcougar]

Well as a follow-up, I've now charged the car 3 times since posting this thread, and have not had any breaker tripping issues. Can't really identify any environmental changes or anything, so for now I'm just chalking it up to random intermittent nuisance trips. I suppose I'll continue to monitor, and if it starts happening again perhaps consider swapping to a non-GFCI breaker.

 

[CoastieM3]

Everything is tight. The plug was installed 2 weeks ago. The car showed up a week ago. I’m not an electrician but am familiar with basic electricity theory/function. Seems to me that a GFI breaker hooked up to a system with additional GFI protection is likely to trip.

Electrician said he’d swap it out.

Swapped mine out. No issues. Charging like a champ, normal heat on breaker/cable, house not on fire.

 

[SteelClouds]

Just a short story about this.. I have a portable GFI breaker adapter in my garage that I use on one my extension cords. The Tesla mobile charger refuses to work on that breaker.. will.not.work.period. I move to the socket with conventional breaker and everybody is happy. In the past 10 years, the Tesla is the only thing that has refused to work with the GFI. I just shrugged and moved it