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Scary issue with Nema 14-50 adapter melting

JimLovewell

Member
Mar 24, 2014
14
0
San Leandro, CA
Update on replacing my Tesla 14-50 adaptor with Hubbell HBL9451C 14-50 plug.
First, (background) I got frightened on March 13, 2014, when my Tesla 14-50 adaptor felt hot. When I measured it using an IR meter it was running 68 °C (154 °F), that is 43°C above ambient. I promptly replace the 14-50 outlet and my adaptor temperature went down to 54°C, which was 32°C above ambient. This for me, is still too hot. 32°C above ambient being too hot is also supported by ANSI/IEEE Standard 242-1986, IEEE Recommended Practice for Protection and Coordination of Industrial and Commercial Power Systems, that recommends insulated conductors maximum safe operating temperature to be 60°C. Note, if this outlet happens to be placed on a southern facing wall on a hot day the ambient temperature could be as high 50 °C. That would give an operating temperature of my Tesla adapter to be 50°C + 32°C = 83 °C! It is not surprising that there has been few fires and/or melted connectors. This is an insufficient safety margin.
When I replace the Tesla 14-50 adapter with a Hubbell 14-50 plug my replacement results were, to get an “apples-to-apples” comparison, a 12°C drop in temperature (were the cord connects to the 14-50 plug). Note, when my Tesla adaptor was running 54°C the cord measured 50°C (28°C above ambient). When I replace the Tesla 14-50 adapter with the Hubbell 14-50 plug the cord measured 38°C (only 16°C above ambient). This is a 43% temperature drop using the Hubbell 14-50 plug versus the Tesla adapter (much better). So, needless to say, I sleep much better at night now when my Tesla starts charging at 40 Amps. at midnight.
Now that I cut off my Tesla 14-50 adaptor and it has one inch leads sticking out, I can take a closer look at the adaptor’s resistance and see where the heat is being generated, the 14-50 contacts versus Tesla round connection pins plus internal connection. Using a four probe micro ohm meter, the total 14-50 adaptor resistance when plugged into a good 14-50 outlet was 4.35 milliohms. The Tesla 14-50 plug (without Tesla’s connectors and internal connections) with outlet connector measured only 1.57 milliohms (0.69 pin 1 + 0.87 milliohms pin 2), that is a 2.78 milliohm reduction or 64%. So that means the Tesla pins plus connector plus and internal wire connections added 2.77 milliohms of resistance (1.22 milliohms red wire + 1.55 milliohms black wire) to the Tesla 14-50 adaptor. So, when it comes to heating up my 14-50 adaptor 64% of the heat comes from Tesla’s round pins + connector + internal connections and 36% of the heat comes from the 14-50 plug and outlet connector. So, to say that high temperatures on the 14-50 outlet was the fault of the outlet may be over simplification. So it would seem, that in the infamous garage outlet fire may have been helped along by the heat added by the Tesla internal wiring versus by just a bad 14-50 outlet alone.
Parting comments, because of the additional resistance Tesla added to their adapter versus a standard 14-50 plug (like the Hubbell HBL9451C) the Tesla adapter should of be de-rated. Note, continuous duty of 50 Amp. plug is only 40 Amps. So, by my calculations the Tesla 14-50 adaptor should have been de-rated by resistance they added by their internal “small” round connectors and internal connections. By my calculations (based on a sample size of one) that would be: Power(14-50) = Power(Tesla adapter) or I[SUB]de-rated[/SUB]^2 x R[SUB]Total[/SUB] = I[SUB]40[/SUB]^2 x R[SUB]14-50[/SUB] or I[SUB]de-rated[/SUB] = Sq-Root(40^2 (1.56/4.35)) = 24 AAC. So, by my calculation the 40Amp. Tesla adaptor should of be de-rated to 24 Amp. to get the same safety margins as a Hubbell 14-50 plug.
Comments / Suggestions ?
I will test the Tesla newly designed 14-50 adapter they are sending out in the mail when I receive it to see if it is any better. More to come, Jim.
 

FlasherZ

Sig Model S + Sig Model X + Model 3 Resv
Jun 21, 2012
7,024
1,013
Not everyone's NEMA 14-50 gets as hot as yours was, so I don't think you can make a blanket statement that it should be "de-rated". There was (is?) something clearly wrong with the mating between adapter and UMC head, and I'm sure the design is being looked at closely. I think we'll have to see how the new gray adapters fair -- do we see events go away, or do the melting issues turn into failure-to-charge issues with the thermal fuse tripping repeatedly?
 

JimLovewell

Member
Mar 24, 2014
14
0
San Leandro, CA
Let us start near the beginning.

A few assumptions we need to make.
This is most likely the largest appliance we leave running/"consuming electricity from the wall"
while we are most likely sleeping.

This by itself should be alarming.

One should ask why didn't we put safety equipment like smoke detectors
as a requirement for installation of charging equipment.

A garage fire could likely lead to loss of life!

Okay there are some alarming thoughts.

I received my car in November of 2012
I sent correspondence and contacted the factory by phone.
To alert them I thought this charging equipment UMC was under size
to run at full rated power in the public's homes.
And should be addressed before mass-market adoption.
You would think a signature owner could influence the development of this automobile.
We find ourselves very frustrated knowing a lot of this could be avoided.
Tesla appears to be taking the shortest route to try and rectify
the reports coming out of the media.

This is unfortunate real engineering is not being looked at.
I encourage all UMC users to install smoke detectors.
I have taken my own advice and have installed smoke detectors.

I would also recommend an electrician visit the home
and verify good torque on connection fasteners socket and circuit breaker.
At least once after initial installation.
If you observe your utility changing a meter you will see them re-torque the connections.

If you have a good understanding of electricity
I'd recommend you perform your own test.

Run the UMC at 40 Amp @240v for 15 minutes.
Disassemble and acknowledge where the heat build up a starting.

Let us as the concerned community
help Tesla solved this problem before it gets completely out of hand.
We all need to raise our hands and say stop the Band-Aids.

Some of the cautions are prudent but they're not the whole solution.
There is a fundamental connection problem with the UMC
that is not being addressed.
Should we petition for a proper recall of the entire UMC charging cable assembly..

And layout safety precautions for the other things that can cause
destructive heeding of this UMC charging assembly.
It would be prudent with the connection like this to a high-powered appliance
that will have the opportunity to be plugged in and out by the general public.

Shouldn't there be a big yellow tag linking safety precautions with this high-powered
connection to the wall?

If the car detects the UMC is being used,
should a safety screen be presented
to remind the non-technical folks how important
plugging this equipment in properly is essential.
And could result in catastrophic harm if not done so.
How do we help the non-technical understand how to work with this technology?

Remember this thing is running at full power
while the user is most likely asleep on a regular basis.

Even if there was no local heating happening in the connector junction,
it would be prudent to recommend some safety precautions and alert systems.
When the home wiring turns out to be questionable.

Does anyone have heat diagnostic photography equipment, that are group could leverage
to visually show what's going on a thermal photograph would be worth a thousand words.

What do you thimk?

lead sleeping dogs lie, or address the fundamental problem.

I don't believe a cable set provided with the automobile should produce substantial heating
when being used at specification.

I very much agree with you we should be installing a smoke detector! Hopefully, you can here it when it goes off. I would also recommend picking up a $17 Cen-Tech Infrared Thermometer from Amazon. I believe checking your equipment’s temperature is the best way to spot trouble. It is what the professionals use.

Amazon.com: Cen-Tech Infrared Thermometer: Home Improvement
 

JimLovewell

Member
Mar 24, 2014
14
0
San Leandro, CA
Not everyone's NEMA 14-50 gets as hot as yours was, so I don't think you can make a blanket statement that it should be "de-rated". There was (is?) something clearly wrong with the mating between adapter and UMC head, and I'm sure the design is being looked at closely. I think we'll have to see how the new gray adapters fair -- do we see events go away, or do the melting issues turn into failure-to-charge issues with the thermal fuse tripping repeatedly?

Yes, I also want to see how the new gray adapters fair. I plan to post the results of my new gray adapter resistance measurement.

I also think for safety’s sake installing a smoke detector is a prudent. Hopefully, you can here it when it goes off.

I also recommend picking up a $17 Cen-Tech Infrared Thermometer from Amazon. I believe checking your equipment’s temperature is the best way to spot trouble. It is what the professionals use.

Amazon.com: Cen-Tech Infrared Thermometer: Home Improvement
 

JimLovewell

Member
Mar 24, 2014
14
0
San Leandro, CA
Not everyone's NEMA 14-50 gets as hot as yours was, so I don't think you can make a blanket statement that it should be "de-rated". There was (is?) something clearly wrong with the mating between adapter and UMC head, and I'm sure the design is being looked at closely. I think we'll have to see how the new gray adapters fair -- do we see events go away, or do the melting issues turn into failure-to-charge issues with the thermal fuse tripping repeatedly?

I also think for safety’s sake installing a smoke detector is a prudent. Hopefully, you can here it when it goes off.
I would also recommend picking up a $17 Cen-Tech Infrared Thermometer from Amazon. I believe checking your equipment’s temperature is the best way to spot trouble. It is what the professionals use.
Amazon.com: Cen-Tech Infrared Thermometer: Home Improvement
 

Mjsais

Member
Aug 12, 2013
97
94
Columbus OH
My UMC 14-50 plug just suffered heat damage. Tesla replace the entire cord. My electrician inspected the 240 plug and replaced it because it also suffered heat damage. My electrician, after inspecting the UMC cable, was concerned about the thickness of the cable in the UMC. According to him, the thickness is in-line with 10-12AWG cable rated for 25 amp max. He says that in order to charge at 40 amp I need 6 AWG cable. Any thoughts?
 

pgiralt

Supporting Member
Jun 16, 2013
1,520
154
Cary, NC
I don't know why he thinks the UMC cable would only have 10 AWG. It's plenty thick enough to have 6 AWG in there. They may even be able to get away with 8 AWG if it is the right type of wire. Regardless, I'm sure Tesla has put adequately thick cable in the UMC, so you shouldn't have to worry.
 

ToddRLockwood

Active Member
Sep 11, 2012
1,317
74
Burlington, Vermont
I thought the UMC cable utilized double wires for each connection, in the interest of keeping the cable as flexible as possible. If the electrician didn't realize this, I can see how he might think the wires were under sized. As for the gauge used between the panel and the NEMA 14-50, #6 would not be a bad idea if the run is longer than 50 feet. I used #6 on my 75 foot run, and I'm seeing no measurable line loss while pulling 40A.
 

pgiralt

Supporting Member
Jun 16, 2013
1,520
154
Cary, NC
Todd, good point - it may very well be double cables, similar to how the cables are run in the Supercharger cables (albeit much larger cables). Either way, I'm sure it'd designed to carry the full 40 amps.
 

Cottonwood

Roadster#433, Model S#S37
Feb 27, 2009
5,088
166
Colorado

FlasherZ

Sig Model S + Sig Model X + Model 3 Resv
Jun 21, 2012
7,024
1,013
There are 50 Amp extension cords for sale that use #8 wire, see Amazon.com: Coleman Cable 1917 8/3 STW 6-50 Welder Extension Cord, Blue, 25-Feet as an example.

If Tesla used a pair of #10 wires each way, that is the equivalent of a #7 each way...

Note that because of their small duty cycles, welders are permitted to use smaller conductors. Components made specifically for welders should never be used for continuous loads unless they're marked as such.

NEC 630 allows for much smaller conductors based on a welder's duty cycle - e.g., a welder with a current rating of > 45 amps can still be hosted on 12 AWG if its duty cycle is 20%. My arc/MIG/TIG welder at home specifies the use of a NEMA 5-20 plug on a 30A circuit.
 

wycolo

Active Member
May 16, 2012
3,068
423
WA & WY
> "Odious Piece of Crap" [#7 on Yahoo Search] [#22 on Google Search] - Real progress being made on this front. :smile:


odius.piece.jpg


Still an 'odious piece of crap'? Sure, but likely the 120v adapter is the safest for MOBILE USE, the one I might plug in and if it didn't get too warm after a few minutes walk away from. 20A or more I would watch like a hawk and have done so the few times I've used them. Mobile Use only.

For home use get a *real* piece of equipment like the Clipper Creek CS-40 (or CS-60, 80, 100 etc) and properly install it. HPWC just too BrookStony to be taken seriously (so there Design Studio!!).

Remember, the watched UMC never bursts into flames, but it knows where you sleep . . .
--
 
Last edited:

Cottonwood

Roadster#433, Model S#S37
Feb 27, 2009
5,088
166
Colorado
Note that because of their small duty cycles, welders are permitted to use smaller conductors. Components made specifically for welders should never be used for continuous loads unless they're marked as such.

NEC 630 allows for much smaller conductors based on a welder's duty cycle - e.g., a welder with a current rating of > 45 amps can still be hosted on 12 AWG if its duty cycle is 20%. My arc/MIG/TIG welder at home specifies the use of a NEMA 5-20 plug on a 30A circuit.

Yes, but whether Tesla decided to use a pair of #10's for an equivalent #7, or a pair of #8's for an equivalent #5, it's all in the ball park of the UMC cable size.

Who had dissected a UMC cable to see what's inside?
 

FlasherZ

Sig Model S + Sig Model X + Model 3 Resv
Jun 21, 2012
7,024
1,013
Yes, but whether Tesla decided to use a pair of #10's for an equivalent #7, or a pair of #8's for an equivalent #5, it's all in the ball park of the UMC cable size.

Who had dissected a UMC cable to see what's inside?

I know that Jim (upthread) has replaced the supply end with a Hubbell 14-50, and TonyWilliams has replaced the other end with J1772.

Tesla's use of parallel conductors inside the unit may be legal, but claiming their use of it in order to use an undersized extension cord doesn't make it right. The NEC makes it legal to put a 45A welder on a 50A or 60A breaker on AWG 12. You'd create a serious fire hazard plugging anything else into that. Just a friendly word of warning for those who see that welder extension cord and think it's ok to use for charging a Tesla.
 

Cottonwood

Roadster#433, Model S#S37
Feb 27, 2009
5,088
166
Colorado
I know that Jim (upthread) has replaced the supply end with a Hubbell 14-50, and TonyWilliams has replaced the other end with J1772.

Tesla's use of parallel conductors inside the unit may be legal, but claiming their use of it in order to use an undersized extension cord doesn't make it right. The NEC makes it legal to put a 45A welder on a 50A or 60A breaker on AWG 12. You'd create a serious fire hazard plugging anything else into that. Just a friendly word of warning for those who see that welder extension cord and think it's ok to use for charging a Tesla.

Yes, but the Welder extension cord that I referenced used #8 AWG wire...
 

FlasherZ

Sig Model S + Sig Model X + Model 3 Resv
Jun 21, 2012
7,024
1,013
Yes, but the Welder extension cord that I referenced used #8 AWG wire...

#8 AWG in SOOW cord is only good for 40 amp rating (NEC table 400.5(A), column B for 2-current carrying conductors) and continuous load requirements need 50A.

That cable is appropriate for a 50A welder but cannot be used for a 50A-rated continuous load application. It's also only STW-rated (so it's not oil resistant).

Product sheet shows 40A too:
8/3 25' STW EXT CORD BLUE W/CLEAR 6-50 PLUG & CONNECTOR | Coleman Cable, Inc.
 

miimura

Well-Known Member
Aug 21, 2013
6,106
5,708
Los Altos, CA
What wire size should Tesla be using for the Mobile Connector? Leviton's 40A EVB40 series EVSE uses a heavy 0.90" OD cable marked "CAROLGRENE ULTRA FLEX(R) ELECTRIC VEHICLE CABLE -- 3C 8 AWG + 1C 18 AWG E333326-8 (UL) EVE 105C DRY 60C WET 600V FT2 - ROHS - MADE IN USA 11/12" for the J1772 handle.
 

FlasherZ

Sig Model S + Sig Model X + Model 3 Resv
Jun 21, 2012
7,024
1,013
Manufacturers follow a slightly different set of rules for internal wiring and listing of devices compared to home infrastructure. Tesla uses special cable rated to 105 degC in the HPWC, although I haven't looked up the termination ratings of terminal blocks and such. It uses EV cable that includes #6 conductors in the coupling connector to the car. The UMC uses a cable with multiple parallel conductors (appears to be 2 14AWG IIRC for each pole).
 

wycolo

Active Member
May 16, 2012
3,068
423
WA & WY
All this nickel & dimeing is giving the wrong impression to Tesla buyers and owners IMHO who should be encouraged to OVER-BUILD their house wiring and EVSE charging station.

Wire is cheap, breaker boxes are cheap, conduit is cheap. Go to Lowes, HomeDepot, etc and see for yourself.

If your house has a sketchy 100 Amp service, then replace it with 200A or even 300A. Move your main breaker out of the house into the yard so you can feed outbuildings (and the house) directly from this new source.

If you are planning on a new feed into garage, where 50A would be minimal base-line, go for 200A. Tell your electrician you have ordered a CS-100 and he should plan accordingly. Don't show him your cheesy UMC and end up with bupkis. Refer to it as a 'garage/workshop' with big plans for the future.

The one thing you do not want to over-size is the final circuit breakers; these must be properly rated for the appliance they actually feed.
--
 

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