Tesla charger keeps tripping our outdoor outlets?
March 22, 2023 7:09 PM Subscribe
We have a Tesla that plugs into a wall socket. The charger trips our GFIs after being plugged in for a few seconds. An electrician came, said it was probably the GFIs, and replaced them, to no effect. What could be going on here? The charging voltage is set as low as it could possibly go.
Can you clarify a few points, you may get better answers if you do:
* where do you live (or more specifically), what voltage / amps/ Hz are you working with?
* No EVs can change the "charging voltage" but you can change the charging "amperage" on some EVs such as Tesla - perhaps you meant the latter?
posted by soylent00FF00 at 7:24 PM on March 22, 2023
* where do you live (or more specifically), what voltage / amps/ Hz are you working with?
* No EVs can change the "charging voltage" but you can change the charging "amperage" on some EVs such as Tesla - perhaps you meant the latter?
posted by soylent00FF00 at 7:24 PM on March 22, 2023
My go-to advice is always to check the wires on the back of the receptacle -- typically you'll find a wire worked itself a little loose, scorch marks, etc. But if you already had an electrician work on it then it's probably fine.
Have you tested the EVSE (the cordset that came with the car) with other outlets? Both GFCI and non-GFCI? The EVSE itself could be defective.
posted by intermod at 8:24 PM on March 22, 2023
Have you tested the EVSE (the cordset that came with the car) with other outlets? Both GFCI and non-GFCI? The EVSE itself could be defective.
posted by intermod at 8:24 PM on March 22, 2023
Did it ever work, or has it always popped the outlet?
posted by hwyengr at 8:37 PM on March 22, 2023 [2 favorites]
posted by hwyengr at 8:37 PM on March 22, 2023 [2 favorites]
you could have poor / damaged wiring from the circuit breaker panel to the receptacle, moisture accumulating in the receptacle, corrosion in the receptacle, or a failing charger cable.
an electrician can diagnose the source of the problem using a leakage detector to isolate where the ground fault (leakage) is occurring.
posted by zippy at 9:36 PM on March 22, 2023
an electrician can diagnose the source of the problem using a leakage detector to isolate where the ground fault (leakage) is occurring.
posted by zippy at 9:36 PM on March 22, 2023
If the GFI is tripping, it's because there is electrical current going to ground (assuming the GFI itself isn't faulty, which seems unlikely given it's new).
You can test whether the issue is somewhere in the car charging system by plugging something else into the same outlet and seeing if it pops and then by plugging the car into a different circuit that is ground fault protected and seeing if it pops - doing this in different premises would eliminate anything in your home wiring. I hope the electrician checked the whole circuit when they installed a new GFI and, if so, it's highly likely the car system is the issue. it's fairly easy for you to test this before you pay an electrician to come back in the unlikely case that both the above tests don't show anything different.
posted by dg at 9:37 PM on March 22, 2023 [3 favorites]
You can test whether the issue is somewhere in the car charging system by plugging something else into the same outlet and seeing if it pops and then by plugging the car into a different circuit that is ground fault protected and seeing if it pops - doing this in different premises would eliminate anything in your home wiring. I hope the electrician checked the whole circuit when they installed a new GFI and, if so, it's highly likely the car system is the issue. it's fairly easy for you to test this before you pay an electrician to come back in the unlikely case that both the above tests don't show anything different.
posted by dg at 9:37 PM on March 22, 2023 [3 favorites]
Best answer: This is a thing with portable car chargers.
One of the things the charger checks for when it's first plugged in to the wall socket is the presence of a connection to ground. The only feasible way to do that test is to run a little bit of current back into the ground pin and see whether that makes its voltage become different from that of the neutral pin. But testing for little trickles of current running back into the ground wire is exactly the fault condition that a GFCI breaker is built to respond to.
Too short/didn't understand:
Grounded US 240V outlets have four connections: two hots, a neutral, and a ground. Each of the hots is at 120V with respect to neutral, but the hots are opposite AC phases which puts them at 240V with respect to each other. Ground and neutral are actually connected to each other, but not directly at the outlet; each has its own wire going back to the breaker panel. So the voltage measured between neutral and ground is always supposed to be zero. And again at the breaker panel, there will be a big thick bond wire connecting both ground and neutral to a metal stake that's actually rammed into the ground.
In normal operation there is never supposed to be any current flowing through the ground wire. Its job is to connect the metal casing on any appliance plugged into the outlet back to the ground stake, so that there can never be a voltage between that exposed metal and the (presumed grounded) body of an appliance user, even if some fault inside the appliance is causing some degree of connection between one of the hots and the metal casing.
The only wires that are ever supposed to have current flowing in them are the hots and the neutral, so that at any instant, any current flowing into the appliance via one of the hots is flowing out again either via the other hot or via the neutral. If there's ever a current flowing in the ground wire, that's a fault condition.
GFCI circuit breakers work by looking for imbalances between the currents flowing in the hot and neutral wires. If those currents don't exactly cancel each other out at all times, then there must be some current escaping into some other circuit that the GFCI isn't monitoring. When that happens, the GFCI will trip and disconnect the hots. That "some other circuit" is often the ground wire. If it's your body instead, the GFCI trip can make the difference between swearing and death.
When you plug your charger into your car, the car becomes an appliance and its bodywork becomes the metal casing. But cars get exposed to many more mechanical stresses than stoves or tumble driers, the chance of some electrical fault that could make the bodywork live is correspondingly higher, and it's not safe to connect the supply mains to a non-grounded car. So chargers are designed never even to start powering the car's charge port if they can't be sure that the outlet they're plugged into is grounded properly. Which means the charger has to verify its own ground connection very early on.
It can't do that simply by looking for a voltage difference between its ground pin and its neutral pin, because that test can't distinguish between those pins having no voltage across them due to (a) being connected to each other at the breaker panel as they should be or (b) the ground pin floating (i.e. not connected to anything at all). Nor can it use the same imbalance trick that a normal GFCI does because again, if the ground pin is entirely disconnected, there will never be an imbalance under normal working conditions. So it has to inject a small probe current into the ground circuit deliberately, and then check to see whether that puts ground and neutral at different voltages. If it does, that means the ground is not connected to neutral anywhere, not even back at the breaker panel, and the charger should report a grounding fault and stop the proceedings.
In practice there actually exist a variety of non-fault conditions that can leak tiny amounts of current into an appliance's ground wire, and GFCI breakers are built to tolerate these. And in theory, the probe currents that the smart chargers use for grounding detection are supposed to be well below the imbalance threshold that would trip a GCFI breaker. But that imbalance threshold is not particularly precise in practice, and some GFCI breakers are sensitive enough that a charger's routine ground presence detection procedure will trip them. There can also exist charger faults that make them use excessive probe currents. So it's all a bit of a crap shoot.
What most people end up doing is using a non-GFCI-protected outlet to plug their portable charger and only that charger into, relying on the charger's own inbuilt GFCI (which it will have, in addition to the ground availability test outlined above) to keep the car safe to be around while charging. If you can't persuade your local electrical inspectors and/or contractors that this is up to code, and your local contractor can't supply you with a less sensitive GFCI that your portable charger doesn't trip, then a hardwired charger might be your only option.
posted by flabdablet at 10:07 PM on March 22, 2023 [23 favorites]
One of the things the charger checks for when it's first plugged in to the wall socket is the presence of a connection to ground. The only feasible way to do that test is to run a little bit of current back into the ground pin and see whether that makes its voltage become different from that of the neutral pin. But testing for little trickles of current running back into the ground wire is exactly the fault condition that a GFCI breaker is built to respond to.
Too short/didn't understand:
Grounded US 240V outlets have four connections: two hots, a neutral, and a ground. Each of the hots is at 120V with respect to neutral, but the hots are opposite AC phases which puts them at 240V with respect to each other. Ground and neutral are actually connected to each other, but not directly at the outlet; each has its own wire going back to the breaker panel. So the voltage measured between neutral and ground is always supposed to be zero. And again at the breaker panel, there will be a big thick bond wire connecting both ground and neutral to a metal stake that's actually rammed into the ground.
In normal operation there is never supposed to be any current flowing through the ground wire. Its job is to connect the metal casing on any appliance plugged into the outlet back to the ground stake, so that there can never be a voltage between that exposed metal and the (presumed grounded) body of an appliance user, even if some fault inside the appliance is causing some degree of connection between one of the hots and the metal casing.
The only wires that are ever supposed to have current flowing in them are the hots and the neutral, so that at any instant, any current flowing into the appliance via one of the hots is flowing out again either via the other hot or via the neutral. If there's ever a current flowing in the ground wire, that's a fault condition.
GFCI circuit breakers work by looking for imbalances between the currents flowing in the hot and neutral wires. If those currents don't exactly cancel each other out at all times, then there must be some current escaping into some other circuit that the GFCI isn't monitoring. When that happens, the GFCI will trip and disconnect the hots. That "some other circuit" is often the ground wire. If it's your body instead, the GFCI trip can make the difference between swearing and death.
When you plug your charger into your car, the car becomes an appliance and its bodywork becomes the metal casing. But cars get exposed to many more mechanical stresses than stoves or tumble driers, the chance of some electrical fault that could make the bodywork live is correspondingly higher, and it's not safe to connect the supply mains to a non-grounded car. So chargers are designed never even to start powering the car's charge port if they can't be sure that the outlet they're plugged into is grounded properly. Which means the charger has to verify its own ground connection very early on.
It can't do that simply by looking for a voltage difference between its ground pin and its neutral pin, because that test can't distinguish between those pins having no voltage across them due to (a) being connected to each other at the breaker panel as they should be or (b) the ground pin floating (i.e. not connected to anything at all). Nor can it use the same imbalance trick that a normal GFCI does because again, if the ground pin is entirely disconnected, there will never be an imbalance under normal working conditions. So it has to inject a small probe current into the ground circuit deliberately, and then check to see whether that puts ground and neutral at different voltages. If it does, that means the ground is not connected to neutral anywhere, not even back at the breaker panel, and the charger should report a grounding fault and stop the proceedings.
In practice there actually exist a variety of non-fault conditions that can leak tiny amounts of current into an appliance's ground wire, and GFCI breakers are built to tolerate these. And in theory, the probe currents that the smart chargers use for grounding detection are supposed to be well below the imbalance threshold that would trip a GCFI breaker. But that imbalance threshold is not particularly precise in practice, and some GFCI breakers are sensitive enough that a charger's routine ground presence detection procedure will trip them. There can also exist charger faults that make them use excessive probe currents. So it's all a bit of a crap shoot.
What most people end up doing is using a non-GFCI-protected outlet to plug their portable charger and only that charger into, relying on the charger's own inbuilt GFCI (which it will have, in addition to the ground availability test outlined above) to keep the car safe to be around while charging. If you can't persuade your local electrical inspectors and/or contractors that this is up to code, and your local contractor can't supply you with a less sensitive GFCI that your portable charger doesn't trip, then a hardwired charger might be your only option.
posted by flabdablet at 10:07 PM on March 22, 2023 [23 favorites]
By the way, I first became aware of this kind of nuisance GFCI tripping after installing 30 PCs in a new school computer lab.
IT equipment power supplies contain small interference-suppression capacitors that leak something like fifty microamps to ground in normal use. Put 30 PCs, 30 monitors, a few printers and a data projector in a room and now we're looking at a standing leakage of a few milliamps. And it's capacitors doing that leaking, so whenever there's a supply disconnection there will be a sudden spike in leakage current on reconnection as all the capacitors charge up at once.
As it happens, that site used to see pretty frequent supply glitches - little blackouts lasting for under one second - as the local switching substation did whatever they do. And every time the lights flickered, the GFCI breaker on the computer lab's subpanel would trip and take the whole lab down. Every other computer in the school would take those glitches in stride like they'd never happened, but the whole lab would just die every time even if only a few PCs were actually in use. Even if none were in use, actually - teachers quite often had to reset that breaker first thing in the morning because a glitch had occurred overnight, and it often took several cycles of flipping off and on before it would stay on. It was really annoying.
What it took to fix it was experimentation to work out how many workstations we could run off a single circuit without tripping the GFCI every time the power came up, which turned out to be about 20, then splitting the lab power outlets across two circuits each with its own breaker.
That's unlikely to work for you, because your trips are being triggered by a single load device rather than thirty workstations in tandem. But it might pay you to get your sparky to run their earth leakage clamp meter over your outdoor outlet's wiring while you start a charging cycle, just to get an idea of how close to the wind your Tesla charger is sailing and how they rate the chance of sourcing a less overzealous yet still code-compliant GFCI breaker for you.
posted by flabdablet at 12:29 AM on March 23, 2023 [6 favorites]
IT equipment power supplies contain small interference-suppression capacitors that leak something like fifty microamps to ground in normal use. Put 30 PCs, 30 monitors, a few printers and a data projector in a room and now we're looking at a standing leakage of a few milliamps. And it's capacitors doing that leaking, so whenever there's a supply disconnection there will be a sudden spike in leakage current on reconnection as all the capacitors charge up at once.
As it happens, that site used to see pretty frequent supply glitches - little blackouts lasting for under one second - as the local switching substation did whatever they do. And every time the lights flickered, the GFCI breaker on the computer lab's subpanel would trip and take the whole lab down. Every other computer in the school would take those glitches in stride like they'd never happened, but the whole lab would just die every time even if only a few PCs were actually in use. Even if none were in use, actually - teachers quite often had to reset that breaker first thing in the morning because a glitch had occurred overnight, and it often took several cycles of flipping off and on before it would stay on. It was really annoying.
What it took to fix it was experimentation to work out how many workstations we could run off a single circuit without tripping the GFCI every time the power came up, which turned out to be about 20, then splitting the lab power outlets across two circuits each with its own breaker.
That's unlikely to work for you, because your trips are being triggered by a single load device rather than thirty workstations in tandem. But it might pay you to get your sparky to run their earth leakage clamp meter over your outdoor outlet's wiring while you start a charging cycle, just to get an idea of how close to the wind your Tesla charger is sailing and how they rate the chance of sourcing a less overzealous yet still code-compliant GFCI breaker for you.
posted by flabdablet at 12:29 AM on March 23, 2023 [6 favorites]
Followup from insteadofapricots via memail, which I'm sure they won't mind if I repost here:
Sounds to me like zippy has it and your outdoor outlets have developed a small standing leakage from hot to ground, quite likely due to moisture ingress, which is not yet severe enough to trip a GFCI breaker on its own but does so when augmented by the charger's ground presence test current.
You should get that fixed. Moisture plus electricity leads to rapid corrosion, and corrosion plus heavy loads like car charging leads to possible electrical fires and/or shock hazards.
If your sparky just turned up, listened to your fault description, replaced a breaker and left, and never actually went over the wiring to all your outdoor outlets with an earth leakage test meter, then I think you should get them back to do just that. That goes double if they, like us, were not initially told that this installation had been working reliably for some months before the GFCI trips started.
Have them visually inspect the insides of all the outdoor outlets as well, and if there's evidence of moisture buildup and/or corrosion, replace those on the basis that their weather seals are probably not working as well as they should.
If you've got multiple outdoor outlets, and they're all on the same GFCI breaker as the one you use to charge your car, and you've got anything plugged into any of the others when the car charging breaker trip occurs, you should try unplugging all of them (not just turning them off) and trying a car charge again.
posted by flabdablet at 11:18 PM on March 23, 2023 [1 favorite]
I do have a follow-up question. One important detail I failed to include in the original post was that the home charger used to work actually; for 3-4 months, it was fine. Then it started tripping the GFIs, and then the new GFIs, once we got the old one replaced.Yes and no. Yes, in that ground probing is still a thing that portable chargers do, and the most likely immediate cause of a GFCI trip that happens right after the charger is connected; no, in that a new failure that started occurring after some months, and still being present after swapping out both the affected GFCI and the portable charger, is a clear indication that there's still an uncorrected fault in place and that fixing that is what you need to do to restore reliable operation.
Does your answer still apply in that scenario?
(We also got a new portable charger in case that was the issue, it was not.)
Sounds to me like zippy has it and your outdoor outlets have developed a small standing leakage from hot to ground, quite likely due to moisture ingress, which is not yet severe enough to trip a GFCI breaker on its own but does so when augmented by the charger's ground presence test current.
You should get that fixed. Moisture plus electricity leads to rapid corrosion, and corrosion plus heavy loads like car charging leads to possible electrical fires and/or shock hazards.
If your sparky just turned up, listened to your fault description, replaced a breaker and left, and never actually went over the wiring to all your outdoor outlets with an earth leakage test meter, then I think you should get them back to do just that. That goes double if they, like us, were not initially told that this installation had been working reliably for some months before the GFCI trips started.
Have them visually inspect the insides of all the outdoor outlets as well, and if there's evidence of moisture buildup and/or corrosion, replace those on the basis that their weather seals are probably not working as well as they should.
If you've got multiple outdoor outlets, and they're all on the same GFCI breaker as the one you use to charge your car, and you've got anything plugged into any of the others when the car charging breaker trip occurs, you should try unplugging all of them (not just turning them off) and trying a car charge again.
posted by flabdablet at 11:18 PM on March 23, 2023 [1 favorite]
God, this might be the issue with my iMiEV. Used to charge just great, then occasional breaker trips, then following a drive battery upgrade it trips the 15A to 10A adaptor in as little as a minute.
There's also a phantom drain on the 12V that used to kill the battery in a week but now does so in a couple of days (or less); I wonder if they're related.
posted by some little punk in a rocket at 12:58 AM on March 24, 2023
There's also a phantom drain on the 12V that used to kill the battery in a week but now does so in a couple of days (or less); I wonder if they're related.
posted by some little punk in a rocket at 12:58 AM on March 24, 2023
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