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Extension Cord with Mobile Charger?

MKandyman

Member
May 1, 2016
51
74
Chicago, U.S.A.
Potential dumb question.

Hopefully in the next 4 weeks I will be taking delivery of my Model 3. I will be moving in about 3 months to a house with a garage where I will install a 50 amp outlet. In the meantime, my townhouse (no garage) has an outdoor 110V outlet (on a 15 amp circuit) which I plan to use for charging (I only drive 20 miles a day, so no worries on the slow charge rate). My only issue is my parking spot is about 30 feet from the outlet, so I had planned to purchase a 25 ft extension cord to use for charging.

The owners manual for the new UMC warns not to use an extension cord. However I feel pretty confident it shouldn’t cause any issues, especially if I buy a brand new outlet (current one has been there a while) and use an extension cord made with 12 gauge wire.

Does anyone else use an extension cord with the UMC? Or, does anyone think my plan is ill advised?

Thanks!
 

TexasEV

Well-Known Member
Jun 5, 2013
7,642
8,470
Austin, TX
Yes, 12 gauge 25 ft. cord should be fine, but don’t use any gauge smaller than that. You can search “extension cord” to find dozens of posts on this topic over the past 5 years. If you have a problem charging, which is unlikely, just turn down the amps.
 
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DanL3

Member
Feb 1, 2018
240
149
Vancouver, Washington
Watch the female plug on the cord to see if it gets warm. If it does cut it off and put on a 20a plug. The 20a plug will have a T for the power lead rather than just a slot. But more important the contacts inside the plug are more robust.

I have burnt up two 12awg wire cords because they used the heavy wire but cheaper plugs. It is always the female plug that is the weak link.
 
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davewill

Active Member
Feb 5, 2014
1,819
1,964
San Diego, CA, US
Keep an eye on the connections. Make sure they aren't getting hot. Avoid lots of plugging and unplugging of the connections. If this were a permanent thing, I'd be telling you to have a new outlet installed, but for 4 weeks you'll be OK as long as you exercise care.
 
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David99

Active Member
Jan 31, 2014
4,850
7,021
Brea, Orange County
The UMC is good at detecting a voltage drop or other issues. I have had the UMC refuse to charge when on an extension cable even though it was a good quality one. A good quality extension cord is something you keep for life and I believe worth paying a little more for.
 

MKandyman

Member
May 1, 2016
51
74
Chicago, U.S.A.
Using regular NEMA 5-15 common household wall receptacles is not ideal. If that’s what you want to do, at a minimum, replace the LOCKING wall receptacle with a NEMA L5-15R

4710

Then, use a quality commercial grade extension cord with the NEMA l5-15 plug.

Thanks for the advice. Just looked quickly and saw that Tesla does not offer an L5-15R adapter for the UMC, meaning I'd need some kind of adapter or special cord to connect the regular 5-15 plug. Doesn't this defeat the purpose of using an L5-15R receptacle?
 

DanL3

Member
Feb 1, 2018
240
149
Vancouver, Washington
The wall receptacle will not be the problem. The problem will be the female end of the extension cord. Change that to a 5-20 plug and you are good to go with the Tesla EVSE as is.
 

TonyWilliams

Active Member
Jun 11, 2012
1,438
758
San Diego - Tesla powered Rav4 EV
Thanks for the advice. Just looked quickly and saw that Tesla does not offer an L5-15R adapter for the UMC, meaning I'd need some kind of adapter or special cord to connect the regular 5-15 plug. Doesn't this defeat the purpose of using an L5-15R receptacle?

You can use an adapter from the 5-15 plug on your UMC to an adaptor from 5-15R to L5-15P. That way, when it burns, it doesn’t burn in your wall.

But, again, I would not ever use a 120 volt 5-15 or 5-20 for the continuous duty loads of charging an EV.

Not a lot of other good options. You can’t use a NEMA 5-20 plug on your UMC (suggested above) since that will overload the 15 amp circuit.

The dual NEMA 5-15 / 5-20 receptacles on an extension cord aren’t any more robust that just a 5-15.

Have you considered NOT using 120 volts?
 

DanL3

Member
Feb 1, 2018
240
149
Vancouver, Washington
The dual NEMA 5-15 / 5-20 receptacles on an extension cord aren’t any more robust that just a 5-15.
Yes, the 5-20 replacement receptacle I put onto a heavy duty 12awg extension cord was clearly more robust than the 5-15 receptacle that came on the cord. I burnt out two of the 5-15 receptacles and then when I put on the 5-20 and ran the same high currents on it and then it was fine and I never had a problem again.
 

yossi

Member
Mar 14, 2018
105
29
brooklyn
for the last 2 months i am on 120ft of cord 15 amp losing a bit power which understandably due to the length
somtimes it drops to on 9A charge instead of 12A but still getting 3MPH
 
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TexasEV

Well-Known Member
Jun 5, 2013
7,642
8,470
Austin, TX
Go to HD, get largest guage cord they have. I found one in Harbor Freight also.
Bad advice. Could you be any more vague?
Regardless of what Home Depot sells or doesn’t sell, you need 10 or 12 gauge extension cord to charge a Tesla in a 15A outlet. This is much heavier than the typical orange “outdoor” extension cords sold at the big box stores.
 

Polly Wog

Member
Dec 4, 2013
464
561
Kihei, Hawaii
@MKandyman, I charged my Model S with a 15 Amp, 50 foot extension cord for 6 months using my UMC with no issues whatsoever. Just make sure that it is rated for 15 Amps for whatever length you get. A quick search on Home Depot's website shows a 14 gauge, 25 foot extension cord for about $20. For the last 3+ years, I've been using my UMC attached to a 50 foot, 50 Amp extension cord with no issues (240 Volt).
 
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taconabag

Member
Feb 4, 2018
10
13
Pittsburgh PA
Yeah extension cord is no problem but the cord gauge is very important. My Volt has the option for 12 amp or 8 amp charging. I charged one day at my dad's house using a 50 foot extension cord at 12 amps and when I came out 4 hours later the extension cord was very hot towards the female end. I unplugged and lowered the charge rate to 8 amps and it was no problem.
 

DanL3

Member
Feb 1, 2018
240
149
Vancouver, Washington
Yeah extension cord is no problem but the cord gauge is very important. My Volt has the option for 12 amp or 8 amp charging. I charged one day at my dad's house using a 50 foot extension cord at 12 amps and when I came out 4 hours later the extension cord was very hot towards the female end. I unplugged and lowered the charge rate to 8 amps and it was no problem.
Yes, the Female end is always the problem. You should use AWG 12 for 15amp but even if you have the biggest wire size, female end on most extension cords will fail if used for a long time at that current. If you look at 10AWG construction cords you will commonly see a tripple plug on the female end because the female end is the week spot.
 

Earthpower

Member
Sep 10, 2017
119
62
NC
Yes, the Female end is always the problem. You should use AWG 12 for 15amp but even if you have the biggest wire size, female end on most extension cords will fail if used for a long time at that current. If you look at 10AWG construction cords you will commonly see a tripple plug on the female end because the female end is the week spot.

What about the following?:
50 Amp RV Extension Cord, Heavy Duty 25 Foot NEMA 14 50 Power Cord for RV, Motor Home, Trailer, Electric Car Level 2 Charging, 6 Gauge, UL Listed Power Cord. 125V/250V two phase (Nema 14-50)

I need an extension cord. Thanks!
 

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