Acceptable extension cords for the UMC

timdorr · Dec 24, 2012

So, the official line from Tesla is that you should never use an extension cord with the UMC. However, I find the length somewhat limiting and was hoping to throw an extension cord in the trunk to act as a life line to emergency charge on a 110v outlet. Does anyone have any experience using the UMC on an extension cord? What sort of gauge and length limits have you run into? I've heard the UMC or car can detect when you're using an extension cord, but that's likely based on voltage fluctuations and will undetectable with a high enough quality of cord. I'm hoping to find one that I can use unofficially

sublimaze1 · Dec 24, 2012

I believe it has been discussed and rendered as such:

Tesla officially states "no extension cords"

But,

If you have a sufficient ga. wire, and correctly attached extension receptacle, you should be okay. Consulting someone with such experience is recommended. After all, RVs use extension cords all the time and, Unless you are Cousin Eddie, things go very well most of the time.

shokunin · Dec 24, 2012

It's possible the UMC can measure the resistance and impedance of the cable to determine if there is an extension cable (undersized) and potentially throw an error. Otherwise for 120v 20a/15a, i'd go for a 10 awg cable, and don't keep it coiled while charging as that will generate additional heat.

FalconNinetyD · Dec 24, 2012

I had ordered a 50A extension cord from Amazon last week, and my mailman said he dropped it off on the porch Saturday, but I never saw the box, nor did my wife. :-( The mailman also remarked that he remembered dropping it off, as he saw the old HP Laserjet 4+ that I had put out for someone who claimed it off my Craigslist "free stuff" post. Me thinks the jack hole who took the printer may have taken the box with my extension cable. Grrr....

As soon as I get a replacement I'll add a data point for those who might want a slightly longer 240V option.

FlasherZ · Dec 24, 2012

It depends upon the length of the cord, the distance from the outlet you're using to the panel, and the current you'll be charging at.

For 120V, to keep the voltage drop within range, you can use a 14 AWG cord if your TOTAL one-way circuit length from the car to the breaker panel is < 50 ft., 12 AWG if your total is < 100 ft., and you'd need to go to 10 AWG if you're at 150 ft. or greater.

For 40A @ 240V (NEMA 14-50), you should use #6, and your total one-way circuit length can be 300 ft, with voltage drop at reasonable levels.

For 24A @ 240V (NEMA 14-30), AWG 10 is good to 200 ft. one-way from breaker panel to the car, go one gauge up (AWG 8) if you need more.

As mentioned, keep your cord to the smallest length possible.

Psullivan · Dec 25, 2012

Mike,

Let me know if you want to come by and charge until your cord comes.

Pat

wycolo · Dec 25, 2012

ModelS arrives home with 16 miles remaining, down from the 271 @ Tesla Shop after a ~245 trip. So need to charge right away. Tractor is in the way so used an old medium duty 50ft extension cord. S shows 112v 12A. Charged ok for 1 1/2 days but then just stopped. Moulded plug on old extension had been running 'warm'. Replaced with 'new' heavy duty ext cord (50ft?) which now shows 117/118v 15A. Charging resumes but still at 2miles per hour rate.
--

efusco · Dec 25, 2012

I purchased the 30' 6Ga version of the Amazon cord linked above ( Camco RV 55195 50 Amp 30 Extension Cord with Handle : Amazon.com : Automotive ).

Just tried it out (finally after having it almost a week!) and it seems to work just fine. I put it in range mode (since it was full in standard) and it is pulling 40amps/10kW without any problem or warnings or anything. It is a very heavy duty cord for RVs, at least as high a gauge as in the wall wiring. I don't intend to use this a lot, but if I need to reach an outlet that's been "ice'd" or that is further away than the UMC will reach it could be a live saver.

I'll let it charge for an hour or so and report back if anything untowards happens.

timdorr · Dec 26, 2012

FlasherZ said:
It depends upon the length of the cord, the distance from the outlet you're using to the panel, and the current you'll be charging at.

For 120V, to keep the voltage drop within range, you can use a 14 AWG cord if your TOTAL one-way circuit length from the car to the breaker panel is < 50 ft., 12 AWG if your total is < 100 ft., and you'd need to go to 10 AWG if you're at 150 ft. or greater.

For 40A @ 240V (NEMA 14-50), you should use #6, and your total one-way circuit length can be 300 ft, with voltage drop at reasonable levels.

For 24A @ 240V (NEMA 14-30), AWG 10 is good to 200 ft. one-way from breaker panel to the car, go one gauge up (AWG 8) if you need more.

As mentioned, keep your cord to the smallest length possible.

Thanks for that info. Very informative and exactly what I was looking for

Raven · Dec 26, 2012

How long is Tesla's stock charge cord?

efusco · Dec 26, 2012

Bleeds On said:
How long is Tesla's stock charge cord?

18' for the UMC
25' for the HPWC

FlasherZ · Dec 26, 2012

timdorr said:
Thanks for that info. Very informative and exactly what I was looking for

No problem. Just remember this is one way from the BREAKER PANEL, not just the receptacle.

FalconNinetyD · Dec 26, 2012

Thanks Pat. I can charge fine if I pull in straight, but prefer to back-in to the garage, so doing that today.

Amazon was awesome, and overnighted a replacement extension cord today, no questions asked.

Psullivan said:
Mike,

Let me know if you want to come by and charge until your cord comes.

Pat

Robert.Boston · Dec 27, 2012

As another data point, I am using a NU-CORD 50' extension cord (NEMA 14-50) to charge at 40A without issue. It's 6/3 + 8/1 copper.

Puyallup Bill · Dec 30, 2012

Robert.Boston said:
As another data point, I am using a NU-CORD 50' extension cord (NEMA 14-50) to charge at 40A without issue. It's 6/3 + 8/1 copper.

Good to hear, as I will be using the same cord, but 36', and at 30 Amps.

FalconNinetyD · Jan 1, 2013

My Camco 50A extension cord works fine. I believe there is a 1-2 volt drop, from 242 to 240-241, but that could have just been related to the time of day when I tested it. The downside is the cord is THICK, probably twice as much as the UMC.

Plug Me In · Jan 23, 2013

Thinking ahead to visits to my Mom's house about 180 miles away from mine. I don't know why I'm trying to save money at this point, but I'll be charging most likely from my Mom's dryer outlet and instead of buying $100 adapter from Tesla, I'm thinking of getting an adapter for the 14-50 plug from an RV site. Anybody tried this? I'm concerned there may be significant voltage drop across two adapters.

FlasherZ · Jan 23, 2013

Plug Me In said:
Thinking ahead to visits to my Mom's house about 180 miles away from mine. I don't know why I'm trying to save money at this point, but I'll be charging most likely from my Mom's dryer outlet and instead of buying $100 adapter from Tesla, I'm thinking of getting an adapter for the 14-50 plug from an RV site. Anybody tried this? I'm concerned there may be significant voltage drop across two adapters.

See the FAQ thread for information on why you might want to avoid this.

Plug Me In · Jan 24, 2013

Thanks Flasher. I was unaware of that excellent resource you put together. I'll probably just buy the Tesla adapter rather than go through all the gymnastics.

giants2001 · Feb 4, 2013

Not sure this is the right thread, but my coworker just pointed me to an interesting device. This device takes two 120v outlets and converts to 240V. Could this actually work and is it safe?

http://www.torquenews.com/1075/how-charge-your-electric-car-120-volt-power-outlets

Acceptable extension cords for the UMC

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