UMC and NEMA 14-50 connector very hot to the touch

UMC and NEMA 14-50 connector very hot to the touch

It’s quite hot here today, upper 80s. Twice on my last charging session charging was stopped. When I went out to check it the charging port light was red. I reseated the UMC connector and it started charging again only to stop again after 10 or so minutes. Any thoughts greatly appreciated.

hcdavis3 | July 14, 2019

Tesla charging is on its own circuit, nothing else there, I have fairly recent 200 amp service. | July 14, 2019

Outside temp of 80 degrees shouldn't make the connector hot to the touch.

Very likely you have a poor connection between the wires from the breaker box connecting to the NEMA 14-50. If it was installed with aluminum wires, this can easily happen. There is a special goo that must be applied when connecting aluminum wires, and many connectors are not even rated to be used with aluminum wires.

hcdavis3 | July 14, 2019

Thanks man all copper 6 awg wire from panel to NEMA 14-50 outlet. | July 14, 2019

Glad it hear it's copper. Ok, it's more likely just a loose connection on the NEMA 14-50 receptacle. If you're qualified, tighten each screw down and confirm the entire wire is captured under the screw. If your not comfortable doing this, get an electrician to inspect and do it.

I find mine warm to the touch, but never hot. For the short term, you might reduce the charging current to 20 or 30 amps until it is resolved.

hcdavis3 | July 14, 2019

Thanks very much. I’m gonna get my electrician over to make sure the connection at both ends is good. Today I was only getting 28 amps vs my normal 32 and the mph were down a bit too. I’ll see how it goes tomorrow night.

jjgunn | July 14, 2019

If ANY part of your charging setup is "hot to the touch" you do not have a proper setup & are at risk of fire.

1) Stop using your current setup
2) Find out what is causing the added heat (need a larger gauge cable??)
3) Repair your setup so it's no longer hot to the touch.

Lonestar10_1999 | July 14, 2019


It’s not uncommon for a current carrying conductor to be damaged or a termination to loosen up. That’s why it’s imperative that a qualified technician check it out and make the necessary repairs.

hcdavis3 | July 14, 2019

Thanks guys. It’s 6 awg from the 50 amp breaker to the 14-50 outlet all copper, on its own circuit. I have a 200 amp service with quite a few available slots.

RES IPSA | July 14, 2019

The other possibility is that the UMC itself is malfunctioning.

RES IPSA | July 14, 2019

Also, since you can only charge at 32 amps using the UMC, you may want to change your breaker to a 40 amp breaker instead of a 50 amp

AWC1014 | July 14, 2019

I’ve never had my UMC slow down due to heat (cut my available power in half) before 20.4.4 but I had it happen multiple times Friday/Saturday on a 20 amp circuit pulling 16 amps that I regularly use with no issue.. It was a slightly warm day (in the shade), but I’ve definitely used it on warmer days with no issue. Im going to see if it becomes a trend.

kevin_rf | July 14, 2019

It is summertime, as everyone had said, the NEMA 14-50 shouldn't be getting that hot, but it might be excessive load on the grid in general dropping your charging voltage and giving you dirty power causing the car to interrupt charging. The two issues might not be related. You might want to check the voltage while charging, it might be lower than normal.

Btw. Halfway through an 1800 mile trip. It's amazing how hot the cables on the 150kw SC's get. I was quite surprised.

hcdavis3 | July 15, 2019

Thanks Kevin and everyone. On another forum another person has the exact problem as me. The common denominator is high ambient temperature in the garage. Yesterday late afternoon when I plugged in for the night it was close to 100 degrees in the garage. I’m completing yesterday’s interrupted charge right now. Connector, cable and block are all cool to the touch. I reseated the 14-50 adapter into the block and unplugged the plug from the outlet and reseated it as well. My local utility sent me an email saying they were aware of a nearby power outage, but I wasn’t here. For now I’m going to schedule charging for early morning and leave the garage door open.

hcdavis3 | July 15, 2019

I do have a call into my electrician.

Tronguy | July 15, 2019

@hcdavis: The thought crosses my mind. Metal expands and contracts as it heats and cools. One would think that this would be accounted for in safety related things like a NEMA connector, and specifically with the torque with which the screws were tightened. But maybe if those screws weren't torqued to the right spec.. Further, there's reasons that the ambient environmental temperature is specified on electrical equipment. Don't know if that's marked on the socket or not..

hcdavis3 | July 15, 2019

Interesting Tron. My electrician is coming this afternoon and I will bring up your thesis.

gballant4570 | July 15, 2019

Depending on your schedule, you might consider setting your home charging to begin at a set time. I have mine set for midnight. I don't have the same heat issue - my car is parked in a two story barn that is surrounded by mature trees (gets a good bit of shade) so the interior doesn't get much above outside ambient temp - but even in hot climates there is some cooling off at night. Getting your charge in between midnight and sunrise might help. Could help with any possible local brownout risks as well.

hcdavis3 | July 15, 2019

Thanks GB. That’s exactly my plan for tonight and until it cools off a bit up here. My electrician is coming this afternoon to check all my connections, I looked at the charge port and the connector, no signs of any issues. I’ll charge from 2:00 AM on, with the garage door open.

lbowroom | July 15, 2019

A little bit of oxidization on the copper between the terminal screw and the wire causes resistance and heat. As this slowly gets worse, the problem gets worse. If you're anywhere near salt air or if you have any chlorine containers near the outlet it can get bad fast.

kevin_rf | July 15, 2019

If you garage has a window, it might be worth leaving it cracked at night. Otherwise you are trapping the heat from the warm car when you pull in at night. Just think, ICE's dump even more heat into the confined space of a garage.

hcdavis3 | July 16, 2019

My electrician just left. All the connections at the outlet were completely tightened. He couldn’t screw them down any more than they were. The car didn’t have an interruption in the charge last night. Hoping this is a one off thermal high ambient temperature event. Anything changes I’ll post.

CRAIGJFIFTY3 | July 16, 2019

While at the super charger yesterday, prompted by this thread, I felt the SC's cable while charging. About half way through it felt very warm, I'd say at least 120*F. At the end of charging I could barely keep my hand on it. It was a warm day, mid to upper 80s. Even the plug and box om my mobile charger gets warm charging @ 16 amps at home.
If you push a lot of electrons through a wire for a long time, it's going to get warm. Tesla was smart to limit the charge current to 75% of circuit rating.