Any Issues Using GFCI Breakers for Charging Circuit?

[Rocky_H]

Point taken and fair enough - although in practice I'm guessing the difference is immaterial as I don't imagine there's a hard-wired EVSE on the market without built-in GFCI.

I still think you're missing it. It's not immaterial at all. ALL EVSE's must have GFCI built into them--no exception. That applies to both plug-in or hardwired. That is not the issue. It's not about what's built-into the EVSE.
There is a very specific difference in practice that is not immaterial, which is that if you are getting a hard wired one, you DO NOT have to use a GFCI breaker, but if you are installing a receptacle for a plug-in device, then you DO have to use a GFCI breaker.

 

[GPinzone]

Hypothetically, if you tell the electrician you need a 14-50 for an RV, you don't need a GFCI receptacle? Yes! I AM getting an RV. Pay no attention to the Tesla in the driveway.

 

[maclean525]

Hypothetically, if you tell the electrician you need a 14-50 for an RV, you don't need a GFCI receptacle? Yes! I AM getting an RV. Pay no attention to the Tesla in the driveway.

It's not hypothetical, that's what you need to tell your electrician because that protects them from liability as well. If you mention car charging they are in a pickle because they can't install against code. To make matters worse 50 amp GFCI breakers are both extremely expensive and out of stock everywhere. Tell them you need a NEMA 14-50 plug installed. Period. If you hardwire the charger there's also no need, as per code, for the GFCI breaker.

 

[Jeremy3292]

I asked Tesla directly and this is the answer I got (came from a "Lead Installation Manager" at Kato Road):

FWIW, I've been charging at a friends house on a 5-20 GFCI outlet pulling 16 amps for multiple hours and have had no issues. House was built in 2012.

 

[Rocky_H]

I asked Tesla directly and this is the answer I got (came from a "Lead Installation Manager" at Kato Road):

View attachment 724271

FWIW, I've been charging at a friends house on a 5-20 GFCI outlet pulling 16 amps for multiple hours and have had no issues. House was built in 2012.

Yeah, that's not surprising. What he is saying is correct about the nuisance and problems it can cause, but that is also recommending very explicitly to violate code. That rule is really irritating.

 

[Jeremy3292]

Yeah, that's not surprising. What he is saying is correct about the nuisance and problems it can cause, but that is also recommending very explicitly to violate code. That rule is really irritating.

2017 or 2020 NEC? 2017 NEC is valid where I live.

 

[Rocky_H]

2017 or 2020 NEC? 2017 NEC is valid where I live.

Yep, that rule was implemented in the 2017 version, so it has been around for a while.

 

[Gauss Guzzler]

To be fair, the rule is sensible and nuisance trips are not typical.

If your home wiring is in fair condition and your GFCI breaker is not grossly out of spec, any nuisance trips should be the fault of Tesla's design, not the NEC's codes.

Also note that many people see nuisance trips with standard breakers as well - and just like with GFCI's, replacing the breaker cures the problem. It's likely that in many of these cases the real cause was just loose screw terminals creating enough heat to trip the breaker's internal overheat protection so it's conceivable that these GFCI interactions are being falsely blamed.

 

[mongo]

To be fair, the rule is sensible and nuisance trips are not typical.

If your home wiring is in fair condition and your GFCI breaker is not grossly out of spec, any nuisance trips should be the fault of Tesla's design, not the NEC's codes.

Also note that many people see nuisance trips with standard breakers as well - and just like with GFCI's, replacing the breaker cures the problem. It's likely that in many of these cases the real cause was just loose screw terminals creating enough heat to trip the breaker's internal overheat protection so it's conceivable that these GFCI interactions are being falsely blamed.

Standard GFCI breakers have a 5mA trip point. EVSE have a 20mA trip. This is needed due to filtering capacitance and other parasitics. You sometimes see the same thing with large motors in swim spas.
The EVSE ground check may trip an upstream GFCI as can these current leakage paths.

 

[CoastieM3]

My brand new 14-50 installed for the M3 had a GFCI breaker. Tripped every night for a week. Asked electrician to swap it out. He did, no trips since. House hasn’t caught on fire either.

He said it happens all the time in SF.

 

[Rocky_H]

Standard GFCI breakers have a 5mA trip point. EVSE have a 20mA trip.

The interesting numbers to compare would be how many mA of current do the EVSEs use to perform their ground checking? It would hopefully be less than 5, but if it's 2 or 3, that is so close that I could easily see one or the other being a little out of tolerance and crossing over.

 

[Jeremy3292]

Standard GFCI breakers have a 5mA trip point. EVSE have a 20mA trip. This is needed due to filtering capacitance and other parasitics. You sometimes see the same thing with large motors in swim spas.
The EVSE ground check may trip an upstream GFCI as can these current leakage paths.

What are GFCI outlet trip point in mA? I've charged on a 5-20 GFCI outlet pulling 16 amps for 8-10 hours with no issues.

 

[mongo]

What are GFCI outlet trip point in mA? I've charged on a 5-20 GFCI outlet pulling 16 amps for 8-10 hours with no issues.

House versions are 5mA.
Edit for clarity: 5mA of imbalance between the two power wires.

 

[Rocky_H]

I've charged on a 5-20 GFCI outlet pulling 16 amps for 8-10 hours with no issues.

The amount of amps you pull on the main circuit lines during operation has nothing to do with it.

It is during startup that the UMC runs a check of the ground pin and puts a tiny bit of current through it to try to see if it seems to be floating or is tied down to 0V pretty solidly. The problem is that putting current on the ground pin is exactly the kind of dangerous operation that a GFCI is intended to find and put a stop to. So it's just a hope that the amount of current it uses for that test is less than the cutoff these outlets and breakers use as their threshold.

 

[Gauss Guzzler]

@mongo Where is the Tesla UMC documented with a 20mA trip current?

Also, it's worth noting that even a 5mA threshold can still be a little bit dangerous - they don't deliberately leak that much during any test.

When you press the test button on an outlet it creates an isolated circuit to do the leak test and doesn't actually leak anything to ground, but internally it leaks enough to legitimately trigger the mechanism by exceeding the 5mA threshold.

By comparison, self-testing GFCI's (like whatever might be inside an EVSE) actually do leak to ground but only a miniscule amount to verify the detection circuitry, not anywhere near enough to self-trip because they are not testing the tripping mechanism, only the detection circuitry.

So I don't see any reason to assume that the trigger threshold of a device is related to the self-test current it uses.

Note that large, old power tools are notorious for tripping old GFCI's. Perhaps EVSE's suffer from the same phenomenon due to their large capacitance/inductance/etc.

 

[mongo]

@mongo Where is the Tesla UMC documented with a 20mA trip current?

Also, it's worth noting that even a 5mA threshold can still be a little bit dangerous - they don't deliberately leak that much during any test.

When you press the test button on an outlet it creates an isolated circuit to do the leak test and doesn't actually leak anything to ground, but internally it leaks enough to legitimately trigger the mechanism by exceeding the 5mA threshold.

By comparison, self-testing GFCI's (like whatever might be inside an EVSE) actually do leak to ground but only a miniscule amount to verify the detection circuitry, not anywhere near enough to self-trip because they are not testing the tripping mechanism, only the detection circuitry.

So I don't see any reason to assume that the trigger threshold of a device is related to the self-test current it uses.

Note that large, old power tools are notorious for tripping old GFCI's. Perhaps EVSE's suffer from the same phenomenon due to their large capacitance/inductance/etc.

I haven't seen Tesla docs on it. The 20mA is from standard EVSE specs. Using that higher trip point seems the require double insulation and/or ground connection validation.
Agree the ground test current is independent from the trip current. And that false upstream trips could be due to filtering / stray capacitance rather than the circuit test. Probably easy to tell which by the timing of the fault trip.