PSA. Another melted NEMA 14-50 receptacle

[eprosenx]

HI all,
Glad I found this forum. I too have a melted outlet. I had a licensed electrician install this years ago. Didn't have any issues until recently. We reach the cord about 10 feet to plug into the car, so I believe that over time, the plug started to wiggle out of the outlet, and/or weakened the contacts inside the outlet with the sideways torque that just the weight of the cord was putting on it. When I noticed it, the plug was slightly out of outlet. Sometimes the cord gets a little tangled and it's likely that we added some torque pulling on it. As you can see from the pictures, this was a close call. The breaker never tripped and the car gave no indication that there was something wrong. I leave the cable plugged in 100% of the time. Since we bought the car years ago, I'll assume that I have the gen 1 UMC.
I'll be making sure that I have a GFCI breaker and the recommended brand of connector this time. Replacing the box too with a properly mounted box. Will probably buy a new UMC too, just to be safe.

Wow! I am glad you and your family are OK!

Can you post pictures or confirm that you have a UMC gen 1?

That wire looks like 8 awg copper to me which is not rated for 50 amps (40a continuous) if it is romex (NM) cable. If indeed it is 8awg romex and you are using a UMC gen 1 then the electrician is at fault as they used the wrong wire (this would be a compliant install if you had a UMC Gen 2 since it is limited to 32a continuous it is ok on a 40a circuit which 8awg NM cable is fine for).

Also, please post what size breaker was installed (photos preferred).

 

[nwdiver]

HI all,
Glad I found this forum. I too have a melted outlet. I had a licensed electrician install this years ago. Didn't have any issues until recently. We reach the cord about 10 feet to plug into the car, so I believe that over time, the plug started to wiggle out of the outlet, and/or weakened the contacts inside the outlet with the sideways torque that just the weight of the cord was putting on it. When I noticed it, the plug was slightly out of outlet. Sometimes the cord gets a little tangled and it's likely that we added some torque pulling on it. As you can see from the pictures, this was a close call. The breaker never tripped and the car gave no indication that there was something wrong. I leave the cable plugged in 100% of the time. Since we bought the car years ago, I'll assume that I have the gen 1 UMC.
I'll be making sure that I have a GFCI breaker and the recommended brand of connector this time. Replacing the box too with a properly mounted box. Will probably buy a new UMC too, just to be safe.

How many Amps do you charge at? Is the body of your UMC secured to anything? I don't think a GFCI would prevent that. IIRC a GFCI measures for a discrepancy in current between the legs. This is to trip the breaker in the event that current is going somewhere it shouldn't (like through a person). Your receptacle melted due to high resistance. The best way to reduce the risk of this moving forward would be to secure the body of the UMC with a holder and lower your charge rate to what you need. I have a HPWC with dual chargers so I can charge at 80A but I rarely charge faster than 20A. Heat generated is the square of the current.

 

[mociaf9]

I'd say that the above is really important.
Everybody who gets a plug-in should have a dedicated EVSE for home charging, whether plug-and-socket or hard-wired, and then have a portable.

A UMC bundle is $300. That's cheap, even for a 32A EVSE.

Most people have no need for both. You only need to take the UMC with you on out of town trips. Leave it plugged in at home otherwise.

Instead of buying a whole second UMC bundle for ~$300, just buy a second 14-50 adapter. It's only $35 or $45 depending on which gen UMC you have. Leave one adapter plugged in to the home receptacle, so you aren't plugging and unplugging "frequently" which is the usual cause of these incidents, and take the UMC body and second adapter with you in the car when you travel.

You're still plugging and unplugging something, but it's something that's theoretically designed for more such uses than the receptacles normally are. Plus you've moved the problematic connection out of the wall where it will dissipate heat better, be easier to note problems, and be less likely to catch things on fire in the case of a catastrophic failure.

 

[AZEVGuy]

Wow! I am glad you and your family are OK!

Can you post pictures or confirm that you have a UMC gen 1?

That wire looks like 8 awg copper to me which is not rated for 50 amps (40a continuous) if it is romex (NM) cable. If indeed it is 8awg romex and you are using a UMC gen 1 then the electrician is at fault as they used the wrong wire (this would be a compliant install if you had a UMC Gen 2 since it is limited to 32a continuous it is ok on a 40a circuit which 8awg NM cable is fine for).

Also, please post what size breaker was installed (photos preferred).

I'm pretty sure my UMC is a Gen 1. It looks like the Gen 1 picture on the Tesla website, not the Gen2. Photos attached.
WRT to the wire AWG...I cut a piece off below the charred insulation and took it to the hardware store to compare. It looks closest to 6 AWG. So I think the wire is to code for the 40 amp breaker installed. Photo attached.
We didn't have any issues for years, so I'm pretty confident that this is caused by increased contact resistance in the receptacle.

 

[AZEVGuy]

How many Amps do you charge at? Is the body of your UMC secured to anything? I don't think a GFCI would prevent that. IIRC a GFCI measures for a discrepancy in current between the legs. This is to trip the breaker in the event that current is going somewhere it shouldn't (like through a person). Your receptacle melted due to high resistance. The best way to reduce the risk of this moving forward would be to secure the body of the UMC with a holder and lower your charge rate to what you need. I have a HPWC with dual chargers so I can charge at 80A but I rarely charge faster than 20A. Heat generated is the square of the current.

I charge at the full 40A. The body of the UMC was not secured and I think this is really the root of the problem. It will be secured from this point forward to provide strain relief to the plug/receptacle. I agree with you that the likely cause of the meltdown was due to increased resistance brought on by lateral force being applied to the plug, loosening the contact force of the receptacle contacts. The plug was also pulled about 1/8th inch out of the receptacle.

 

[eprosenx]

I charge at the full 40A. The body of the UMC was not secured and I think this is really the root of the problem. It will be secured from this point forward to provide strain relief to the plug/receptacle. I agree with you that the likely cause of the meltdown was due to increased resistance brought on by lateral force being applied to the plug, loosening the contact force of the receptacle contacts. The plug was also pulled about 1/8th inch out of the receptacle.

Can you see the writing on any part of the wire that is not charred? Is it romex (NM) cable? It really looked like 8awg (and this would match up with the 40a breaker), but it is hard to tell from photos.

That is a UMC gen 1 for sure. Hopefully you can just replace the melted adapter and the UMC will be just fine for future use.

So regardless of 6 awg or 8 awg, one way or another the initial install was done wrong. The UMC gen 1 is a 40 amp continuous load device. Either the wire and the breaker were undersized, OR just the breaker was undersized. The first is a fire hazard and the second is a nuisance trip issue. The electrician screwed up one way or another. If you can safely take pictures of your panel with the cover off we might be able to more easily tell if it is 8 awg or 6 awg (though still hard without a reference).

We most commonly see this failure mode when the terminals were not properly tightened on the back of the receptacle, if some insulation was accidentally inserted into the clamp, or they worked their way loose after repeated thermal cycling (from charging daily). Probably because they were torqued wrong to begin with.

It is hard to say if wear on the plug or lateral forces caused this issue. I tend to think not (unless it was enough force to reduce the contact force on one side clip of the receptacle) but who really knows without extensive laboratory testing.

If you ensure you have the right size breaker and wire and get a high quality receptacle and mount / strain relieve it, there will be zero issues going forwards I am sure. But with all that said, I am a massive fan of the Wall Connector as it reduces some of these failure modes. (also, the UMC gen 2 has thermal monitoring in the plug end and would likely have avoided this incident that way - and it only draws 32a max so it is acceptable on 8 awg copper romex and just a 40a breaker)

Good luck and do report back what you find out and what your final solution is!

 

[eprosenx]

Instead of buying a whole second UMC bundle for ~$300, just buy a second 14-50 adapter. It's only $35 or $45 depending on which gen UMC you have. Leave one adapter plugged in to the home receptacle, so you aren't plugging and unplugging "frequently" which is the usual cause of these incidents, and take the UMC body and second adapter with you in the car when you travel.

You're still plugging and unplugging something, but it's something that's theoretically designed for more such uses than the receptacles normally are. Plus you've moved the problematic connection out of the wall where it will dissipate heat better, be easier to note problems, and be less likely to catch things on fire in the case of a catastrophic failure.

I do *not* recommend this. The adapter connection to the UMC (either generation) is not intended for this many insertion cycles. I think this is worse than inserting and removing every day from a NEMA receptacle.

I would much rather replace a NEMA receptacle regularly and maybe a $35 UMC adapter once in a while than a $275 UMC.

 

[nwdiver]

So regardless of 6 awg or 8 awg, one way or another the initial install was done wrong.

Not necessarily...

the meltdown was due to increased resistance brought on by lateral force being applied to the plug, loosening the contact force of the receptacle contacts. The plug was also pulled about 1/8th inch out of the receptacle.

 

[eprosenx]

Not necessarily...

A UMC Gen 1 by definition is a 40a continuous load draw device. That requires a 50a breaker minimum (and since it is on a 14-50 in this case, 50a is also the max allowed).

 

[AZEVGuy]

Can you see the writing on any part of the wire that is not charred? Is it romex (NM) cable? It really looked like 8awg (and this would match up with the 40a breaker), but it is hard to tell from photos.

That is a UMC gen 1 for sure. Hopefully you can just replace the melted adapter and the UMC will be just fine for future use.

So regardless of 6 awg or 8 awg, one way or another the initial install was done wrong. The UMC gen 1 is a 40 amp continuous load device. Either the wire and the breaker were undersized, OR just the breaker was undersized. The first is a fire hazard and the second is a nuisance trip issue. The electrician screwed up one way or another. If you can safely take pictures of your panel with the cover off we might be able to more easily tell if it is 8 awg or 6 awg (though still hard without a reference).

We most commonly see this failure mode when the terminals were not properly tightened on the back of the receptacle, if some insulation was accidentally inserted into the clamp, or they worked their way loose after repeated thermal cycling (from charging daily). Probably because they were torqued wrong to begin with.

It is hard to say if wear on the plug or lateral forces caused this issue. I tend to think not (unless it was enough force to reduce the contact force on one side clip of the receptacle) but who really knows without extensive laboratory testing.

If you ensure you have the right size breaker and wire and get a high quality receptacle and mount / strain relieve it, there will be zero issues going forwards I am sure. But with all that said, I am a massive fan of the Wall Connector as it reduces some of these failure modes. (also, the UMC gen 2 has thermal monitoring in the plug end and would likely have avoided this incident that way - and it only draws 32a max so it is acceptable on 8 awg copper romex and just a 40a breaker)

Good luck and do report back what you find out and what your final solution is!

It is NM Romex. I don't see any markings on the wire insulation. There isn't enough of the outer NM sheath sticking through the box to read the AWG either. I took the breaker panel cover off, but the NM sheath is stripped all the way back to where the Romex comes into the panel. And like I said the wire insulation has no markings. I'm very confident that it is 6AWG. The 8AWG at the hardware store was definitely smaller in diameter. It's hard as hell to bend those wires. There was no signs of overheating at the breaker or the wires, just at the receptacle. So it would seem that something failed within the receptacle, not at the breaker. The breaker has never tripped in the four years that I've had this install. Even with this recent meltdown.
I don't think it is wear on the plug or the receptacle due to repeated plugging/unplugging, because we never unplug it. Perhaps with repeated thermal cycling, the wire terminal screws loosened, but they seemed pretty tight when I removed the charred receptacle. I'm going to ensure I have the Hubbell receptacle and will definitely mount the charger to prevent any forces on the plug. I also bought a new Gen1 14-50 plug adapter off the Tesla website, since that was charred as well.
Thanks for all your suggestions.

 

[Brandoelectric]

HI all,
Glad I found this forum. I too have a melted outlet. I had a licensed electrician install this years ago. Didn't have any issues until recently. We reach the cord about 10 feet to plug into the car, so I believe that over time, the plug started to wiggle out of the outlet, and/or weakened the contacts inside the outlet with the sideways torque that just the weight of the cord was putting on it. When I noticed it, the plug was slightly out of outlet. Sometimes the cord gets a little tangled and it's likely that we added some torque pulling on it. As you can see from the pictures, this was a close call. The breaker never tripped and the car gave no indication that there was something wrong. I leave the cable plugged in 100% of the time. Since we bought the car years ago, I'll assume that I have the gen 1 UMC.
I'll be making sure that I have a GFCI breaker and the recommended brand of connector this time. Replacing the box too with a properly mounted box. Will probably buy a new UMC too, just to be safe.

Typical loose connection. Put some staaaank on it when tightening the screw next time.

I’ve seen electricians use a screw gun with a Phillips tip to tighten the terminal screws, when actually it’s a #2 square tip. If you use the right tool this won’t happen

 

[MY1stEV]

According to the Hubbell 9450 installation instructions, 75 lb-in of torque is the proper amount of "staaaank" when tightening down the the terminal screws, but not many DIY'er own a torque screwdriver.

 

[hw13]

This outlet was installed about a year ago, the loose connection between the adapter blade and the outlet caused the adapter to melt into the receptacle.

That doesn't look like it's caused by the plug blade or socket, it looks like bad wiring.

 

[3sr+buyer]

That doesn't look like it's caused by the plug blade or socket, it looks like bad wiring.

The outlet in the photo says Leviton, but does not look like the current Leviton outlets.

However, the current Leviton outlets plug holes have contacts only about half of the length of the holes, so the contact area with the plug blades is small compared to other outlets. If this was true for the old Leviton outlets, that could have contributed to overheating.

Note that the plug heads for the current Tesla EVSE have temperature sensors that signal the car to reduce charging rate if too much heat is detected.

 

[Chrushev]

Weird, when I plug into questionable NEMA 14-50R the car will give me over temperature warning and bumps down the charge level. Weird that its not doing it for you folks and instead melts the outlet.

I have a Leviton and a Hubbell that I use interchangeably, both in metal enclosures. Both never warmer than ambient temperature when charging at 32A. The thing is, if you got a short, then even Hubbell will melt, you have a runaway heat problem. Hubbell is chunkier, bigger heatsink, but will melt eventually too. So if properly installed, into metal enclosure (to help with heat dissipation) a $15 Leviton will do fine. Something like Hubbell allows bigger margin of error, and decreases chance of poor connection (due to better construction), but by no means is unmeltable.