Almost burned the house down

[gaspi101]

Charging was interrupted in the middle of the night. Found the garage fuse was tripped and the UMC in this condition. It looks to me like the Nema 14-50 box melted down—do you folks think it was the fault of the nema plug or the UMC? It was professionally installed and has been working for 3 years without problems.

 

[Baluchi]

That's scary. Out of curiosity, what was the amperage of the circuit that fed that outlet, and how many amps did you charge at?

 

[gaspi101]

That's scary. Out of curiosity, what was the amperage of the circuit that fed that outlet, and how many amps did you charge at?

It’s a 100 amp box with two circuit breakers connecting this UMC and a Wallcharger—two Teslas were charging simultaneously, each on their own breaker at 32amps, the Wallcharger’s fuse did not trip and charging finished just fine. The Nema, however, looks like it didn’t make it more than an hour from the moment it started charging.

 

[KyleDay]

Most likely a cheap 14-50 socket or faulty installation (securing the wire insulation to the outlet instead of directly securing the wire)m causing heat resistance).

 

[RedTesY]

The problem would be where the heat was. Looks like most of the heat was in the UMC plug. Have your installer come and open up the receptacle and inspect/check the receptacle connections. If it all looks good behind the cover plate, time to talk with Tesla!

 

[gaspi101]

The problem would be where the heat was. Looks like most of the heat was in the UMC plug. Have your installer come and open up the receptacle and inspect/check the receptacle connections. If it all looks good behind the cover plate, time to talk with Tesla!

The receptacle is melted down completely…. As is the UMC plug…looks like the red live wire is peeled off and severed…I bet it was over tightened, came off a little, touched something and bam.

 

[Tam]

...melted down...

It's called "mobile" for a reason.

That's one of the risks of a removable plug so a hardwired High Power Wall Connector is preferable.

First-generation plugs didn't have a heat sensor so it was recalled with replacements.

Gen2 plugs are better but the risk of being overheated is still there.

 

[KJD]

It would be interesting to know who made the outlet, in other words what brand is it ?

Some of the outlets sold in the big box stores are not so good for heavy usage like charging a car for hours on end.

Master Thread: Definitive 14-50 NEMA Outlet Guide

Comparing the 2 outlets recommended by Tesla with the sub $10 big box model as well as the one I think you should buy 1. Hubbell 9450a 2. Bryant 9450fr 3. Cooper 5754n 4. Leviton 279-S00 The Hubbell and Bryant are far and away the superior product here and since Hubbell owns Bryant and these...

teslamotorsclub.com

 

[brucet999]

The receptacle is melted down completely…. As is the UMC plug…looks like the red live wire is peeled off and severed…I bet it was over tightened, came off a little, touched something and bam.

"Came off, touched something and bam" does not melt down the outlet case and plug. Shorting to the case would have cause a huge spark, local melting and tripped the breaker instantly. The photo shows no melting of the copper strands, which would certainly have happened in the event of the wire coming in contact with the opposite terminal or with ground.

A loose connection, however, could have been arcing for some time and heating up the whole assembly to the melting point of plastic parts.

Also, "Almost burned the house down" title is hugely hyperbolic. No sign even of scorching drywall, much less evidence of nearly catching the house on fire.

 

[gaspi101]

"Came off, touched something and bam" does not melt down the outlet case and plug. Shorting to the case would have cause a huge spark, local melting and tripped the breaker instantly. The photo shows no melting of the copper strands, which would certainly have happened in the event of the wire coming in contact with the opposite terminal or with ground.

A loose connection, however, could have been arcing for some time and heating up the whole assembly to the melting point of plastic parts.

Also, "Almost burned the house down" title is hugely hyperbolic. No sign even of scorching drywall, much less evidence of nearly catching the house on fire.

Thanks for the info, it perhaps looks worse than it is to my untrained eye. So you think it was just a loose connection in the box?

 

[Big Earl]

I’m glad you’re okay. Large electrical shorts like this can be scary.

Is this a Leviton brand receptacle? If so, this exact issue has been discussed in several threads over the years. This is why many people on TMC recommend installing a Hubbell, Bryant or Cooper brand NEMA 14-50 receptacle ($50-100) instead of Leviton ($10) or some other cheap brand. The difference in build quality is immediately apparent when comparing them side by side.

Even better than that is a hard-wired Wall Connector as it has fewer possible points of failure.

Master Thread: Definitive 14-50 NEMA Outlet Guide

Comparing the 2 outlets recommended by Tesla with the sub $10 big box model as well as the one I think you should buy 1. Hubbell 9450a 2. Bryant 9450fr 3. Cooper 5754n 4. Leviton 279-S00 The Hubbell and Bryant are far and away the superior product here and since Hubbell owns Bryant and these...

teslamotorsclub.com

Everyone using a NEMA 14-50 outlet for home charging should check the brand of outlet and take corrective action if necessary.

 

[Johnny Vector]

This is almost certainly a Leviton receptacle. You can tell by the Phillips/flatblade screw head in the photo. Hubbell/Bryant receptacles have hex socket head (Allen key) clamp screws.

This, in my mind, is the biggest problem with Leviton's 14-50s. Getting the correct torque for #6 or #8 wire with a Phillips screwdriver is very difficult. Doing it with an Allen key is easy. If the wire is not clamped sufficiently, it can work for years, all the while slowly moving toward failure. Without sufficient preload on a clamp screw, any motion can make it back out. Motion, for instance, caused by thermal changes. In my business the thermal changes we have to watch out for are caused by going in and out of direct sunlight once every 97 minutes; for a charging outlet the thermal changes are caused by charging cycles. Regardless of how tight the joint is, it will heat up enough to make the parts expand when current is flowing. Without the required preload on the screw, that expansion and contraction can cause it to slowly back out. Which reduces the preload further, until finally it's no longer making a good electrical connection. Then you get resistive heat or arcing, either of which can ruin your day.

This is why the manufacturer provides a torque spec for tightening the clamp screw. For a 14-50, it's a substantial amount; enough to hurt your wrist if you're trying to do it manually with a Phillips screwdriver. Don't ask how I know. The use of Phillips screw clamps is reason enough to never use the cheap Leviton receptacles. (I have heard they also make a better line, which may be better, I dunno. The Bryant is only about $40, just spec that.)

 

[rwiegand]

I'd ask your fire department to sent their investigator to look at it. They are typically well trained to figure out exactly what went wrong in this kind of situation.

 

[gaspi101]

This is almost certainly a Leviton receptacle. You can tell by the Phillips/flatblade screw head in the photo. Hubbell/Bryant receptacles have hex socket head (Allen key) clamp screws.

This, in my mind, is the biggest problem with Leviton's 14-50s. Getting the correct torque for #6 or #8 wire with a Phillips screwdriver is very difficult. Doing it with an Allen key is easy. If the wire is not clamped sufficiently, it can work for years, all the while slowly moving toward failure. Without sufficient preload on a clamp screw, any motion can make it back out. Motion, for instance, caused by thermal changes. In my business the thermal changes we have to watch out for are caused by going in and out of direct sunlight once every 97 minutes; for a charging outlet the thermal changes are caused by charging cycles. Regardless of how tight the joint is, it will heat up enough to make the parts expand when current is flowing. Without the required preload on the screw, that expansion and contraction can cause it to slowly back out. Which reduces the preload further, until finally it's no longer making a good electrical connection. Then you get resistive heat or arcing, either of which can ruin your day.

This is why the manufacturer provides a torque spec for tightening the clamp screw. For a 14-50, it's a substantial amount; enough to hurt your wrist if you're trying to do it manually with a Phillips screwdriver. Don't ask how I know. The use of Phillips screw clamps is reason enough to never use the cheap Leviton receptacles. (I have heard they also make a better line, which may be better, I dunno. The Bryant is only about $40, just spec that.)

This is excellent advice, thank you so much.

 

[gaspi101]

I'd ask your fire department to sent their investigator to look at it. They are typically well trained to figure out exactly what went wrong in this kind of situation.

This sounds like a good idea, but I’d be concerned that they’d send someone that would instead do a code compliance audit of my entire house and then I’d have a nightmare situation.

 

[ItsNotAboutTheMoney]

Can I also ask how often you leave the UMC plugged in, and how often you carry it with you?

 

[gaspi101]

Can I also ask how often you leave the UMC plugged in, and how often you carry it with you?

It was permanently affixed—I bought an extra just to keep it plugged in and be able to carry the other in the car wherever I went…ironic. so now I just bought a new UMC from the Tesla store…anyone know why the hell used UMCs are sold on ebay for much higher than the Tesla store? Are Tesla store deliveries backed up?

also, thanks to the great advice from folks on this thread, i bought a new Hubbel receptacle, hope i Never have this issue again! https://www.amazon.com/dp/B00IPBMUKY/ref=cm_sw_em_r_mt_dp_QRHHRRG8H24WRF77XAT3?_encoding=UTF8&psc=1

It fortunately, it appears quite common as a consequence of the cheap receptacle installed by my electrician. even the Amazon reviews for this item talk about exactly this, even with pictures. I consider the mystery solved, thanks to you awesome people on this forum.

 

[brucet999]

I’m glad you’re okay. Large electrical shorts like this can be scary.

Is this a Leviton brand receptacle? If so, this exact issue has been discussed in several threads over the years. This is why many people on TMC recommend installing a Hubbell, Bryant or Cooper brand NEMA 14-50 receptacle ($50-100) instead of Leviton ($10) or some other cheap brand. The difference in build quality is immediately apparent when comparing them side by side.

Even better than that is a hard-wired Wall Connector as it has fewer possible points of failure.

Master Thread: Definitive 14-50 NEMA Outlet Guide

Comparing the 2 outlets recommended by Tesla with the sub $10 big box model as well as the one I think you should buy 1. Hubbell 9450a 2. Bryant 9450fr 3. Cooper 5754n 4. Leviton 279-S00 The Hubbell and Bryant are far and away the superior product here and since Hubbell owns Bryant and these...

teslamotorsclub.com

Everyone using a NEMA 14-50 outlet for home charging should check the brand of outlet and take corrective action if necessary.

I just looked at my NEMA 14-50 outlet but could find no manufacturer info, only NEMA 14-50 stamped on one edge and 240V 50A along the opposite edge. How can I tell if mine is Leviton or not? Maybe I'll pull it tomorrow and see what kind of terminal screws it has.

 

[Johnny Vector]

I just looked at my NEMA 14-50 outlet but could find no manufacturer info, only NEMA 14-50 stamped on one edge and 240V 50A along the opposite edge. How can I tell if mine is Leviton or not? Maybe I'll pull it tomorrow and see what kind of terminal screws it has.

One difference is the Bryant/Hubbell ones are larger diameter. The part that sticks through the cover plate, I mean.

Leviton: about 2-1/8 inch diameter
Bryant/Hubbell: about 2-1/2 inch diameter

Note that because of the larger diameter you need to get a different cover plate if you replace a Leviton with a Bryant/Hubbell. The cover plates they have at your local box store won't fit. I got mine from from Gordon Electric Supply if I recall correctly, but there are several online electric supply retailers that will work. You can probably get it at Grainger too if you have a burning need to pay more.

 

[MontyFloyd]

This is almost certainly a Leviton receptacle. You can tell by the Phillips/flatblade screw head in the photo. Hubbell/Bryant receptacles have hex socket head (Allen key) clamp screws.

This, in my mind, is the biggest problem with Leviton's 14-50s. Getting the correct torque for #6 or #8 wire with a Phillips screwdriver is very difficult. Doing it with an Allen key is easy. If the wire is not clamped sufficiently, it can work for years, all the while slowly moving toward failure. Without sufficient preload on a clamp screw, any motion can make it back out. Motion, for instance, caused by thermal changes. In my business the thermal changes we have to watch out for are caused by going in and out of direct sunlight once every 97 minutes; for a charging outlet the thermal changes are caused by charging cycles. Regardless of how tight the joint is, it will heat up enough to make the parts expand when current is flowing. Without the required preload on the screw, that expansion and contraction can cause it to slowly back out. Which reduces the preload further, until finally it's no longer making a good electrical connection. Then you get resistive heat or arcing, either of which can ruin your day.

This is why the manufacturer provides a torque spec for tightening the clamp screw. For a 14-50, it's a substantial amount; enough to hurt your wrist if you're trying to do it manually with a Phillips screwdriver. Don't ask how I know. The use of Phillips screw clamps is reason enough to never use the cheap Leviton receptacles. (I have heard they also make a better line, which may be better, I dunno. The Bryant is only about $40, just spec that.)

THIS ^^^^ perfectly explains the challenge of wiring connectors, especially high W.

What satellites you design for, if you can divulge.

(as to OP, nothing to add to comments)