2nd Gen mobile connector "ground loss"

[pdp1]

Background: I installed my own 50A breaker and 14-50 NEMA outlet and use the mobile connector to charge my Model 3 every night. I've been having this reoccurring problem, on average once a week, where the mobile connector gives a 2x red blink of the 'T', which according to the manual, suggests there is a "loss of ground." It crops up randomly, usually when the charger is plugged into the car but not charging and waiting for the scheduled time to come... no sudden movements of the mobile connector like accidentally kicking it. Once it did happen when the car was actively charging (I got an interrupted charge notification) and I think once this even happened when the mobile connector wasn't plugged into the car, and only plugged into the 14-50 outlet. To fix it, I first unplug the 14-50 adapter from the outlet, then unplug the 14-50 adapter from the mobile connector, and do the reverse to put it all back together.

Anyway, a loose ground seems kind of unlikely to me because if there was indeed a "loss of ground", it would suggest there is bad ground somewhere that is still "kind of" connected since I have been charging just fine otherwise. Since it's been exactly 4 weeks, this alleged "bad connection" probably would have tripped breaker or even toasted an outlet or plug somewhere by now, neither of which has happened. Nevertheless, I checked all my ground connections, at the breaker box and at the 14-50 outlet, they seem solid. There is literally only about 2 feet of 6/3 Romex between the breaker and the outlet. I'm leaning toward saying the problem is in the mobile connector or the 14-50 adapter.

All that said, is there anything I can check to make absolutely sure it wasn't something in my wiring that is causing this? I want to make sure I covered all the bases before trying to swap my mobile connector at Tesla, or even just swapping the 14-50 adapter.

 

[eprosenx]

Background: I installed my own 50A breaker and 14-50 NEMA outlet and use the mobile connector to charge my Model 3 every night. I've been having this reoccurring problem, on average once a week, where the mobile connector gives a 2x red blink of the 'T', which according to the manual, suggests there is a "loss of ground." It crops up randomly, usually when the charger is plugged into the car but not charging and waiting for the scheduled time to come... no sudden movements of the mobile connector like accidentally kicking it. Once it did happen when the car was actively charging (I got an interrupted charge notification) and I think once this even happened when the mobile connector wasn't plugged into the car, and only plugged into the 14-50 outlet. To fix it, I first unplug the 14-50 adapter from the outlet, then unplug the 14-50 adapter from the mobile connector, and do the reverse to put it all back together.

Anyway, a loose ground seems kind of unlikely to me because if there was indeed a "loss of ground", it would suggest there is bad ground somewhere that is still "kind of" connected since I have been charging just fine otherwise. Since it's been exactly 4 weeks, this alleged "bad connection" probably would have tripped breaker or even toasted an outlet or plug somewhere by now, neither of which has happened. Nevertheless, I checked all my ground connections, at the breaker box and at the 14-50 outlet, they seem solid. There is literally only about 2 feet of 6/3 Romex between the breaker and the outlet. I'm leaning toward saying the problem is in the mobile connector or the 14-50 adapter.

All that said, is there anything I can check to make absolutely sure it wasn't something in my wiring that is causing this? I want to make sure I covered all the bases before trying to swap my mobile connector at Tesla, or even just swapping the 14-50 adapter.

Do you just have a single main electrical panel in the house? No disconnect or separate panel at the meter base outside?

I ask because neutral and ground for the house must be tied together at one and only one location - this is at the main service panel (which could be the meter base if you have a disconnect out there). With that being said: You need to verify that neutral and ground are properly tied together at that location. Then you need to verify that your neutral feed from the utility is connected properly into your main panel (tight, etc...).

The reason I ask all of this is because as far as I know, there is no way for the UMC to be able to test that your ground connection is good. What it *can* test is to make sure that it sees 120v from each hot phase leg to ground. The reason it can "see" this voltage potential is because neutral and ground are tied together at the main service panel. If they were not properly tied together, or your neutral back to the utility transformer at the street was loose somehow, it would not see the proper voltage potential and would throw the error you are seeing.

A loose neutral on the utility feed is extremely dangerous and leads to fried electronics and can burn your house down.

Are you by chance seeing any weird voltage fluctuations in the house on 120v things like lights or outlets? If not, I would not worry too much and this is likely not your issue.

At the end of the day, this might straight up be a faulty UMC or an issue with your vehicle.

 

[pdp1]

Do you just have a single main electrical panel in the house? No disconnect or separate panel at the meter base outside?

I ask because neutral and ground for the house must be tied together at one and only one location - this is at the main service panel (which could be the meter base if you have a disconnect out there). With that being said: You need to verify that neutral and ground are properly tied together at that location. Then you need to verify that your neutral feed from the utility is connected properly into your main panel (tight, etc...).

The reason I ask all of this is because as far as I know, there is no way for the UMC to be able to test that your ground connection is good. What it *can* test is to make sure that it sees 120v from each hot phase leg to ground. The reason it can "see" this voltage potential is because neutral and ground are tied together at the main service panel. If they were not properly tied together, or your neutral back to the utility transformer at the street was loose somehow, it would not see the proper voltage potential and would throw the error you are seeing.

A loose neutral on the utility feed is extremely dangerous and leads to fried electronics and can burn your house down.

Are you by chance seeing any weird voltage fluctuations in the house on 120v things like lights or outlets? If not, I would not worry too much and this is likely not your issue.

At the end of the day, this might straight up be a faulty UMC or an issue with your vehicle.

I have a main disconnect at the meter outside which has two breakers:
1) To a 125A subpanel in the garage (this panel feeds the whole inside of the house, including the 50A 14-50 for the Tesla
2) To the central A/C compressor.

The ground is connected to the neutral at the main disconnect outside. Since this house is 36 years old and no electrical fires have occurred in that time span, I'm skeptical it would be a loose neutral or that the ground isn't properly tied out there. However, the ground wire coming from the 14-50 outlet into the garage subpanel is run pretty close to the neutral bar in the garage subpanel, I wonder if maybe its ground is accidentally touching the neutral bar.

Thanks for all the good info, I'll digest it and check a few more things when I get home later today.

 

[eprosenx]

I have a main disconnect at the meter outside which has two breakers:
1) To a 125A subpanel in the garage (this panel feeds the whole inside of the house, including the 50A 14-50 for the Tesla
2) To the central A/C compressor.

The ground is connected to the neutral at the main disconnect outside. Since this house is 36 years old and no electrical fires have occurred in that time span, I'm skeptical it would be a loose neutral or that the ground isn't properly tied out there. However, the ground wire coming from the 14-50 outlet into the garage subpanel is run pretty close to the neutral bar in the garage subpanel, I wonder if maybe its ground is accidentally touching the neutral bar.

Thanks for all the good info, I'll digest it and check a few more things when I get home later today.

Good to know. Yes, neutral and ground should *only* be bonded outside at that main panel with the meter. You have the right idea.

While ground and neutral touching on the panel in the garage is not a great thing, it would not cause the error you are seeing.

As to if the neutral was loose causing issues:

This is actually a somewhat common failure. Over time a neutral wire works its loose. It can happen at the main panel, the meter base, or even very commonly back at the utility transformer connection.

If you don't have voltage fluctuations on any 120v stuff then this is likely not the issue, but I just throw it out there since it is a dangerous failure mode (if not all that common).

 

[pdp1]

The ground from the 14-50 is definitely not touching the neutral bar in the garage subpanel. The 2x red blink of the ‘T’ led happened again when I got home tonight after I plugged in the UMC to the car. I again jiggled and reseated the 14-50 adapter on both the 14-50 plug end and the UMC end and all 5 green lights showed up normal again.

Another strange thing, I have the car scheduled to charge starting at 1am. At 1:50am I opened the Tesla App to make sure the car was charging. When the car finally woke up after opening the app, it was charging, but based on the range reported it JUST started charging. So basically it means it didn’t adhere to the schedule to start charging at 1am and only started charging after I woke it up with the app. I wonder if this “glitch” has to do with the other intermittent ground loss I experience.

After about 15 minutes of charging, I went down to the garage to check on the charger to see if there were any abnormalities. I felt the 14-50 outlet, the 50a breaker, and the UMC itself, none felt even slightly warm to the touch (it’s around 45-50F in my garage at night if that matters). I guess I’ll just keep monitoring the issue. I’m glad it doesn’t happen that often, but at the same time, I wish it would happen more often so I could debug it faster

 

[eprosenx]

The ground from the 14-50 is definitely not touching the neutral bar in the garage subpanel. The 2x red blink of the ‘T’ led happened again when I got home tonight after I plugged in the UMC to the car. I again jiggled and reseated the 14-50 adapter on both the 14-50 plug end and the UMC end and all 5 green lights showed up normal again.

Another strange thing, I have the car scheduled to charge starting at 1am. At 1:50am I opened the Tesla App to make sure the car was charging. When the car finally woke up after opening the app, it was charging, but based on the range reported it JUST started charging. So basically it means it didn’t adhere to the schedule to start charging at 1am and only started charging after I woke it up with the app. I wonder if this “glitch” has to do with the other intermittent ground loss I experience.

After about 15 minutes of charging, I went down to the garage to check on the charger to see if there were any abnormalities. I felt the 14-50 outlet, the 50a breaker, and the UMC itself, none felt even slightly warm to the touch (it’s around 45-50F in my garage at night if that matters). I guess I’ll just keep monitoring the issue. I’m glad it doesn’t happen that often, but at the same time, I wish it would happen more often so I could debug it faster

Do you have a multimeter? I would put it in AC voltage test mode and check the voltage from each hot conductor to the ground pin. No need to test the neutral pin since it is completely unused by the UMC.

As far as the charge time thing: We have seen issues like this reported before. Like the car sleeps too hard and does not wake up at the right time to charge. I doubt it is related to your ground issue though.

I think after using the multimeter that it is time to call Tesla. My best guess is a hardware issue. You have done your diligence at this point.

P.S. One other thing is you could try charging at 120v for a night to see if the same thing happens. It would rule out a lot of things if it also faulted on 120v.

 

[pdp1]

Do you have a multimeter? I would put it in AC voltage test mode and check the voltage from each hot conductor to the ground pin. No need to test the neutral pin since it is completely unused by the UMC.

As far as the charge time thing: We have seen issues like this reported before. Like the car sleeps too hard and does not wake up at the right time to charge. I doubt it is related to your ground issue though.

I think after using the multimeter that it is time to call Tesla. My best guess is a hardware issue. You have done your diligence at this point.

P.S. One other thing is you could try charging at 120v for a night to see if the same thing happens. It would rule out a lot of things if it also faulted on 120v.

Your PS section got me thinking, I have a friend who doesn't user her 14-50 adapter, I should borrow it for a few weeks to try it out!

Also, I think I narrowed down the problem to the 14-50 plug area. The red T came up again and all I had to do was wiggle the 14-50 end of the adapter to get the green LEDs to come up again. So it could be the adapter or the 14-50 socket itself, but I still suspect the 14-50 adapter since I find it less likely there would be a discontinutiy between the socket and the wires I screwed into the back of the socket.

 

[KevinThornberry]

I had a similar issue driving me nuts. I was checking everything associated with the HPWC. Turned out it was a dirty port on the charging cable where i plugged into the car. Not enough to keep it from charging all the time, but enough to sporadically give me 'short" errors. I figured i'd check the handle that plugs into the car. I was doubtful this was the fix but the last thing i was willing to get involved in before calling an electrician. I turned off the breaker then took pipe cleaners and cleaned out the tiny ports on the bottom of the charging cable where it goes into the car. There was substantial build up in them. I cleaned out the large ports as well while i was there.
It worked. it's been 5 days charging at full amps with zero interruptions. -Maybe this can help you.

I also know that the charger will 'reattempt' charging a few times on it's own after a fault is detected every 15 minutes or so.
This may explain it not beginning to charge on time as it may attempted to restart a few times.

 

[pdp1]

I borrowed my friend's 14-50 adapter and used it for a while and the 2x blink on the red 'T' still occurred. So that removed the 14-50 adapter as a possible culprit. What's left is now either the 14-50 socket the adapter plugs into or something wrong with the mobile connector.

I still find it hard to believe something is wrong with the 14-50 socket, and eyeballing it, it doesn't look like there is anything wrong with it, unless maybe the ground pin socket is loose and not holding the ground pin from the 14-50 adapter in tightly. That said, I also investigated the mobile connector a little closer and discovered that if I "drop" the mobile connector from 1 inch or so off the ground, when it hits, I can hear some metal rattling/vibrating coming from it. This doesn't seem normal to me, and could be the culprit of my intermittent problems. Can anyone else verify if they hear the same sound from their mobile connector?

 

[enixneo]

Hey @pdp1 I'm in the exact same scenario you're describing. Just recently I got a "ground fault" error message on my Mobile Connector Gen2 when plugged into my NEMA 14-50 outlet. If I swap out the NEMA 14-50 adapter for a NEMA 5-15 adapter, the car charges just fine. So it's not a problem with the Mobile Connector.

Do you have a multimeter? I would put it in AC voltage test mode and check the voltage from each hot conductor to the ground pin. No need to test the neutral pin since it is completely unused by the UMC.

@eprosenx In my case, when I test the NEMA 14-50 outlet, L1-to-neutral gets 120v, L2-to-neutral gets 120v. L1-to-ground and L2-to-ground are each supposed to be 120v but when I test L1-to-ground it's 30.3v and L2-to-ground is 23.7v. What could be causing these readings? Again, the issue just started a few days ago. It's never happened before. The Mobile Connector always remains connected, it doesn't ever get unplugged re-plugged. And it's out of the way, so it hasn't been bumped into or pressed against.

I borrowed my friend's 14-50 adapter and used it for a while and the 2x blink on the red 'T' still occurred. So that removed the 14-50 adapter as a possible culprit. What's left is now either the 14-50 socket the adapter plugs into or something wrong with the mobile connector.

I still find it hard to believe something is wrong with the 14-50 socket, and eyeballing it, it doesn't look like there is anything wrong with it, unless maybe the ground pin socket is loose and not holding the ground pin from the 14-50 adapter in tightly. That said, I also investigated the mobile connector a little closer and discovered that if I "drop" the mobile connector from 1 inch or so off the ground, when it hits, I can hear some metal rattling/vibrating coming from it. This doesn't seem normal to me, and could be the culprit of my intermittent problems. Can anyone else verify if they hear the same sound from their mobile connector?

Whatever came of this? What ended up being the problem and the fix?

 

[eprosenx]

@eprosenx In my case, when I test the NEMA 14-50 outlet, L1-to-neutral gets 120v, L2-to-neutral gets 120v. L1-to-ground and L2-to-ground are each supposed to be 120v but when I test L1-to-ground it's 30.3v and L2-to-ground is 23.7v. What could be causing these readings? Again, the issue just started a few days ago. It's never happened before. The Mobile Connector always remains connected, it doesn't ever get unplugged re-plugged. And it's out of the way, so it hasn't been bumped into or pressed against.

Whoh, this is seriously bad. Somehow you have a disconnected ground or perhaps ground and neutral conductors not properly “bonded” (which should only happen back at the main service entrance).

The fix is probably not difficult here, but it may require an electrician if you are not comfortable safely working on high voltage stuff.

I would probably be opening up the panel it is connected to and testing there and/or opening the receptacle up to check it’s wires.

 

[enixneo]

Somehow you have a disconnected ground or perhaps ground and neutral conductors not properly “bonded” (which should only happen back at the main service entrance).

I would probably be opening up the panel it is connected to and testing there and/or opening the receptacle up to check it’s wires.

I have some degree of experience as I installed the NEMA 14-50 outlet myself over a year ago when I first got the car. With guidance, I can perform basic troubleshooting steps.

As you said, there's the possibility the problem is at the receptacle. But since I never unplug the outlet, I'd like to start at the electrical panel.

If I'm following you correctly, you suspect the bare ground wire or the neutral wire are crossing somewhere (likely at the electrical panel)? Or do you suspect they are not properly attached to the neutral bus bar? How would I go about identifying the location of the fault?

I did recently replace a faulty circuit breaker (to an unrelated bedroom) on the electrical panel the day before I started getting this error. I'm wondering if something got moved around or a connection got loose while I was working on that.

 

[eprosenx]

I have some degree of experience as I installed the NEMA 14-50 outlet myself over a year ago when I first got the car. With guidance, I can perform basic troubleshooting steps.

As you said, there's the possibility the problem is at the receptacle. But since I never unplug the outlet, I'd like to start at the electrical panel.

If I'm following you correctly, you suspect the bare ground wire or the neutral wire are crossing somewhere (likely at the electrical panel)? Or do you suspect they are not properly attached to the neutral bus bar? How would I go about identifying the location of the fault?

I did recently replace a faulty circuit breaker (to an unrelated bedroom) on the electrical panel the day before I started getting this error. I'm wondering if something got moved around or a connection got loose while I was working on that.

My assumption is that the ground wire from the EV receptacle is not connected either at the receptacle end OR at the panel end (sounds more likely).

Note that if your electrical panel is the “service entrance” then the neutral bus and ground bus are equivalents as neutral and ground are bonded together at that point. But if it is any kind of a subpanel then they are separate. The issue in that case could also be between the subpanel and the main panel or in the main panel.

So yeah, I would open it up and make sure the ground is nice and tight.

Take lots of pictures and post them here if needed.

Also, you can take measurements in the panel that may help. Try probing the ground wire from the EV receptacle and then the “hot” busses / infeed lugs, etc... to see if there is proper voltage potential there.

 

[enixneo]

Note that if your electrical panel is the “service entrance” then the neutral bus and ground bus are equivalents as neutral and ground are bonded together at that point. But if it is any kind of a subpanel then they are separate. The issue in that case could also be between the subpanel and the main panel or in the main panel.

The good news is that I only have the one main panel. No subpanels.

My assumption is that the ground wire from the EV receptacle is not connected either at the receptacle end OR at the panel end (sounds more likely).

So yeah, I would open it up and make sure the ground is nice and tight.

Take lots of pictures and post them here if needed.

Also, you can take measurements in the panel that may help. Try probing the ground wire from the EV receptacle and then the “hot” busses / infeed lugs, etc... to see if there is proper voltage potential there.

This is my electrical panel. On the bottom there is my 6/3 romex for the NEMA outlet. I put the ground wire to the left bus and the neutral to the right bus as the homebuilder put all the bare copper wires on the left and the coated white wires on the right. I checked and they are securely screwed in. I tested the EV ground on the left to a hot wire from the above breakers and it reads 120v.

I think that's strange, everything's right and I'm really dreading disassembling the outlet receptacle. So I decide to plug the car in for the umpteenth time and lo and behold.

It says everything's charging fine...
I literally haven't done anything differently since the last time it gave me an error code except talk to you and read through a dozen forum posts. So thanks for fixing it Hopefully it keeps up. Is there anything further you suggest I check?

 

[TheRFMan]

Since it’s working again, It might be worth checking that L1 and L2 are now both 120V to ground at the outlet. Seeing that your outlet is so close to the panel, if you still have some weird voltage between line and ground at the outlet, try measuring between L1 or L2 at the outlet and the ground bar at the panel. If that is 120V but the line to ground at the outlet is not, you might have a defective outlet, or a damaged ground conductor in the Romex cable.

 

[pdp1]

Hey @pdp1 I'm in the exact same scenario you're describing. Just recently I got a "ground fault" error message on my Mobile Connector Gen2 when plugged into my NEMA 14-50 outlet. If I swap out the NEMA 14-50 adapter for a NEMA 5-15 adapter, the car charges just fine. So it's not a problem with the Mobile Connector.



@eprosenx In my case, when I test the NEMA 14-50 outlet, L1-to-neutral gets 120v, L2-to-neutral gets 120v. L1-to-ground and L2-to-ground are each supposed to be 120v but when I test L1-to-ground it's 30.3v and L2-to-ground is 23.7v. What could be causing these readings? Again, the issue just started a few days ago. It's never happened before. The Mobile Connector always remains connected, it doesn't ever get unplugged re-plugged. And it's out of the way, so it hasn't been bumped into or pressed against.



Whatever came of this? What ended up being the problem and the fix?

My problem ended up being a faulty 14-50 socket/outlet, my guess a loose ground? I replaced the socket/outlet and everything has been good for almost 2 years now

 

[enixneo]

Seeing that your outlet is so close to the panel, if you still have some weird voltage between line and ground at the outlet, try measuring between L1 or L2 at the outlet and the ground bar at the panel. If that is 120V but the line to ground at the outlet is not, you might have a defective outlet, or a damaged ground conductor in the Romex cable.

That's an excellent point. Since it's working fine now, I'm going to give it a week to see if any errors come up. But then I'll make sure to do this test just to confirm.

My problem ended up being a faulty 14-50 socket/outlet, my guess a loose ground? I replaced the socket/outlet and everything has been good for almost 2 years now

Thanks for filling us in. I'm not necessarily out of the woods yet. If I get any errors, my next step is to do as you did and test the outlet itself. All part of the DIY experience.

 

[SilverSp33d3r]

If you can recal did you have any other appliances running when you saw the 30v to ground?

 

[enixneo]

All right, it's been about a month and I wanted to provide some final updates in case anyone like me comes across this thread while googling any similar issues. This may help provide some info to any other DIY installers out there.

Somehow you have a disconnected ground or perhaps ground and neutral conductors not properly “bonded” (which should only happen back at the main service entrance).

This ended up being the problem. I did a second inspection of all the connections and found out that this bolt was not tightened all the way so the ground wire wasn't making full contact with the ground bar. It was making contact and working fine for 18+ months but must have jiggled lose when I had to remove the breaker panel a month ago to replace an unrelated faulty breaker. I have now tightened it all the way then pulled and tugged on it to make sure it could not get loose again.

Since it’s working again, It might be worth checking that L1 and L2 are now both 120V to ground at the outlet. Seeing that your outlet is so close to the panel, if you still have some weird voltage between line and ground at the outlet, try measuring between L1 or L2 at the outlet and the ground bar at the panel. If that is 120V but the line to ground at the outlet is not, you might have a defective outlet, or a damaged ground conductor in the Romex cable.

I now have normal reading all across. But I appreciate this bit of knowledge. I'll now know to check this if I need to troubleshoot anything new.

If you can recal did you have any other appliances running when you saw the 30v to ground?

I cannot recall. It's possible a washing machine or dishwasher was running but I can't be sure.

 

[!igs]

I've been having this reoccurring problem, on average once a week, where the mobile connector gives a 2x red blink of the 'T', which according to the manual, suggests there is a "loss of ground." It crops up randomly, usually when the charger is plugged into the car but not charging and waiting for the scheduled time to come...

I'm on my second 2nd gen UMC and it does this intermittently well. It's a complete POC. I hope Tesla makes cars better than they make power cables because so far they are 0/2.

For those that haven't been following along, it's not a problem with my circuit it's a problem with the mobile connector. It throws the error on different outlets, different outlet types, different adapters, when not charging. I was able to borrow someone else's mobile connector and it did not throw any errors on the same outlets with the same adapters.