Very hot nema 14-50 adapter

I just noticed that my nema adapter gets very hot. I have been using it for a month now and I don't remember it being so hot. It uncomfortably hot and the heat conducts up about 2 feet of the external wire conduit. The cable up to the transformer is also very warm but the connector to the car is slightly warm only. The run of #8 wire is less than 20 feet and the rest of the conduit from the box to just 2 feet before the plug is cool. I think it is the adapter that is the problem. I am taking the charging cable and adapter to tesla tomorrow. Anyone else have this problem?

You say "uncomfortably hot" which is a bit vague. If you have access to an IR thermometer use that to take an actual measurement. My rule of thumb is that unless it's too hot to hold without burning yourself, you don't need to worry. Even still, there's a long way to go between what will burn a person and what will cause a fire. High current loads WILL get pretty warm...

The connector should not get that hot unless you have a bad connection. Replace the 14-50 receptacle about $10 at Lowes or home depot. If that doesn't solve the problem also replace the mobile 14-50 connector, more expensive. Make sure there is no slack when the plug is fully inserted. The heating is costing a bit of effeciency however if it doesn't get overly hot, it is no big deal. You should be able to hold the connector while the car is charging with no problem.

Did you use aluminum wire? If so, it needs to be coated with anti-oxidant to avoid oxidation where it touches copper, though really that shouldn't be an issue for years after the install. You could also have broken conductors in the cable that increase the resistance. Do you see a voltage drop at the car when charging starts?

The wires are typically rated for 60C so if you can hold your hand on it at all it is in no danger of melting the insulation and starting a fire.

The other way to think about this is voltage loss. You can measure the voltage with the plug out (no load) and then see how much voltage that the car reports when charging. I would think that no more than a few volts, maybe 5. Hopefully others can see how much drop they get and report back. If it is more than that then the losses in the wire and/or connector are reducing your charging rate. BTW, I thought that #8 wire was OK for a 50 Amp circuit, but that #6 wire was recommend for "continuous use", which is what you are doing when you are charging overnight.

I have the same issue. The heat starts in my cable right after the 14-50 adaptor (not between the 14-50 and the wall outlet but between where the adaptor connects to the universal end) and the cable gets too hot to hold for more than a few seconds nearest the adaptor and gets progressively less hot the closer to the module in the cable that I get. Right after the adaptor the cable is about as warm as I would expect it to be. And this was not how it acted when I first got it either.

I have found that if I lower the current via touchscreen to around 25 amps then it stays at a reasonable temperature. I just sent an email to ownership earlier today and was surprised to see this posting a few hours later.

murraypetera - Thanks. I just received delivery notice and have an electrician on standby to install the NEMA 14-50 in my garage. I'll be sure he uses #6 wiring.

My electrician wanted to put in #8 saying it was code, but I insisted on #6, because of continuous usage, even though the run was fairly short from the "box". The voltage lost in the wires is voltage not charging your car.

This is from FlasherZ's FAQ over on TMC re NEMA 14-50R, much of it Greek to me:

Note: All wire sizes assume copper conductors!

For wire-in-conduit, 8 AWG THHN (dry locations) or THWN (wet locations) is sufficient to carry 50 amps, but many electricians will use 6 AWG to ensure that there is enough headroom. The ground conductor must be a minimum size of 10 AWG.

For “Romex” (NM-B cable), it must be sized for the 60 degC rating. This means that 8/3+ground NM-B may not be used for 50A, and 6/3+ground NM-B must be used. Note that type NM cable must be protected from damage (e.g., must be run inside a wall) and cannot be exposed. If you must run wiring on the outside of a wall, below 7' above the floor, you must use conduit. Type NM cable may be run in conduit as long as it does not run outside.

If these conductors will ride in the same conduit as another circuit, they must be “de-rated” and 6 AWG is required.

Yes, more than 15 min. or so requires #6. Your wiring is too light for home charging.

The continuous use part of it means you derate the wire, breaker, and outlet by 25% -- that is why the car will only charge at 40A. So, you are already covered on the continuous use aspect. If this is in a garage that might get hot in the summer, then you also have consider derating for ambient temperature.

The majority of the time I have found a loose screw on the 15-50 receptacle. Turn off the breaker take out the outlet and see if the screws holding the wire turn half a turn or so clockwise. That little bit can be enough to create a lot of heat.

If it feels like the heat is starting at the Tesla box with the charge light then get the charge cable replaced.

Most devices are rated at least to 60 degrees C. That's 140 degrees F. Too hot to touch so the whole touch thing is tough to call. Still it should not get that hot.

I just took my laser temp tester out to the garage and the outlet on the wall is in the 60 degree F range. The Tesla charge box with the light is at 90.5 degree F. The cable within a foot of the Tesla box is around 89 degrees. My car has been charging for an hour. To me everything felt normal.

2011 code definition for continuous load is now anything that runs for more than 3 hours. You should be using a #6 like most here are saying.

Not all municipalities are using 2011 code.

I meant 14-50

@blephneiben - if you understand a couple of terms it becomes a bit less Greek:

'Romex' means that individual metal wires are covered in plastic, then the bundle of 3 or 4 wires is itself wrapped in a sheath - what most people would call a 'cable' as opposed to a 'wire'. This is generally what is found in the walls of a house.

8/3+ground means four wire cable - 3 of them are #8 AWG (usually two hot and one neutral), plus a ground wire.

6/3 means the same, except #6 AWG. #8 wire is 0.1285" in diameter and #6 is 0.1620". The bigger diameter means lower resistance (generally) and so can carry higher current with lower losses and less heating.

When using conduit (metal or plastic pipe), individual wires can be used instead of sheathed cable, because the conduit protects the individual wires.

'Derating' means using a bigger wire than would normally be used, so that it doesn't get as hot when run together with other wires on a different circuit in the same conduit.

There's obviously a lot more to it than this, but that will hopefully allow the paragraph to make sense.

I just wired my garage (almost done that is) and for the extra cost of copper $2.04/ft instead $1.04/ft I put in awg #2 instead of #6 and I can now upgrade to the HPC which I just added to my order.

#2 is a pain to pull but better than doing it twice. I'll wire the 14-50 for day 1 ( I pulled a run of #6 for this) and when HPC arrives or I have time ill hook it up.

I ordered the 40 and in my mind the smaller the battery the quicker I will need to charge. I am still very disappointed that Tesla does not offer the super charger for the 40.

Good luck with your plug. It is always better to over spec wiring than under.

The 40kWh is not a long-distance car, and attempting to create a SC network to accommodate it would require at least double the number of stations, as its range is less than half the 85's, and it would take about twice as long per mile to charge even with SC's, as charge rate is a matter of % of max charge for the battery.

Wrong tool for the job.

I had the same adapter heating up problem when I first got my MS. I was using a used 14-50 outlet. It turned out that that outlet wasn't making good contact with the adaptor. By replacing the 14-50 outlet with a new one I solved the problem completely.

I'm trying to figure out what part of 'cable' heat you are concerned about. I'll just say this, my UMC gets quite warm at 40A. I turned the current down to 30A to make it run a bit cooler and make me sleep better. Anytime there is a transfer of power, it will be met with some resistance. That gets turned into heat. Mind you the amount of heat that cable can handle and my human tissue can handle are two totally different things. I just took some numbers for reference, hope this helps...
The two measurements are of the potato sized adapter module and the cable from it to the car. Highest temps were noted, and occurred where the cable looped over itself.
Standing room temp of cable and adapter were at 65
Charging at 30A it climbed to 89 for the adapter and 99 for the cable.
Bumped charge rate to max at 40A and temps rose to 100 for the adapter and 115 for the cable.
At this point I measured the 14-50 plug coming out of the wall and it was at 78 degrees.
So, to me standing in a garage at 65 degree, the charge cable seems like a good hand warmer...

thanks for all the suggestions.

I'm still waiting for my 40 kWh. I got a quote from Mr. Electric to install the 50 amp breaker, a 35ft run, and the NEMA 14-50 outlet of $1,100. No way. A friend / electrician said he'd do the basic install for $150 if I ran the wire. My questions are: is all 6/3 wire stranded? Is there such a thing as solid 6/3? Also, do I need to run this in conduit to install in a dry garage?

Thanks in advance for any info.

I used solid #6 wire from Home Depot. I'm not an electrician, but as I undertand it surface mounted wires require conduit by code. And even if you don't care about code, I'd never run unprotected wires carrying 40A along a wall. WAY too dangerous. Been zapped by 240V a few times and it isn't a pleasant experience.

@Barryfin - if the garage isn't finished, you can drill holes through the 2x4s and run it there (or above rafters if they aren't used for storage). Your local code may vary though - in general, unless you are certain of what you are doing, hire an electrician.

Doing it yourself will probably invalidate all your home insurance. "Penny-wise and pound foolish." Electrical fires are a very, very, very, ..., very high risk.


"2011 code definition for continuous load is now anything that runs for more than 3 hours. You should be using a #6 like most here are saying."

My electrician who installed the #8 wire insists he is to code. Where can I find the 2011 code for continuous load that requires going to #6


If youre in Seattle area Brady at Volt Tech( installed my 14-50 w/#6 for $250. He was great and very familiar w/Tesla requirements. Was referred to me by multi property owner/builder. $1000 +is ridiculous unless they're redoing your walls! And use conduit!

I paid $594 about a 30 ft of #6 run through the garage ceiling in flex conduit and then down the wall in hard conduit. We also pulled a set of #12 for a 110V circuit at the same location.

The $1,100 quoted also included $240 for a City of Las Vegas permit. (Still $860 for a 35ft run is insane. When I told him it seemed high, his answer was "You're spending $100,000 on a car, what's another $1,100?" This was in a finished garage, and not run in / through any walls.)

Is anybody else getting permits?

Still not sure if I need 6/3 solid or if stranded is OK.

And thanks for the advise - I will use conduit!

@tranhv68 - you don't need to account for continuous load twice. 40A continuous requires derating of 25%, which means you count it as if it were 50A intermittent. Any conductor rated to carry 50A is fine for 40A continuous. Local codes may vary, but according to NEC #8 is fine for 50A at room temperature.

If your ambient temperature may get high, or if you have multiple conductors in the same raceway (ie, conduit), then you have to derate it further, and in that case #8 won't be enough.

@BarryFinn - if you are running copper, 35ft is not going to be cheap and if it is on the surface they will have to install conduit. That seems a bit high, but not outrageous. Solid or stranded is fine.

@Barryfinn, several other owners and owners to be in Las Vegas have made contact, if you would like to be included in the group, just let me know and I'll send you an email, presumably to your cox account. I can also give you some insight on what I did for a 14-50, FWIW.


That would be great.


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