240 Extension Cords

240 Extension Cords

Sorry if this is a duplicate, but I searched this forum and didn't find a thread like this.

I know that Tesla says not to use extension cords, but I just returned from my first road trip (90 mi each way) and I almost got stranded. the place I stayed had a great 240 plug near a parking spot, but it was just about 15' beyond the standard charger that comes with the car. So, I moved to another spot where I could use their 110. that worked fine, but at only 3 mi per hour, I needed over 24 hours to recharge the "90 miles" that I had driven which drained my engine 140 mi equivalent (4 guys in the car and it was cold).

I don't want to have that "range anxiety" again, so I would like to find a 15' - 30' extension cable that will get me closer to the 20-25 mi/hr charge rates that I get at home.

I saw that one guy bought this RV extension cord on Amazon, but he didn't say if it actually worked and charged in that low 20 mi range.

Anyone have experience with this or another RV extension cord and if they will work for occasional (5x per year) travel?

jat | 20 marts 2013

That should be fine.

Captain_Zap | 20 marts 2013

The Model S is supposed to be capable of sensing the use of an extension cord and refuse to charge. If the extension cord is appropriate for the job it might not sense the extension cord and let your charge. The shorter the run the better. I think that you can find a cord in 15' lengths.

FlasherZ at TMC is the expert on such matters. You might try a search there.

Sanjuro | 20 marts 2013

I have the 15' Camco extension cord from Amazon, because I'm too lazy to back my car in. It works fine - I'm getting 20-25 m/hr. I don't know about the 30' one though.

shop | 20 marts 2013

I bought the 30' one and used it as a test to test a dryer plug (240v, 30a). It worked fine. Tesla can only tell if you are using an extension cord if it senses a large enough voltage drop when it ramps up the current. And that will only happen if you use an undersized extension cord. Those rv extension cords are sized correctly for 50 amps, so no problem.

iholtzman | 20 marts 2013

I purchased a 15ft 50amp extension cord from Camping World. I brought it to the Tesla service center in Chicago. They tested it and it worked fine.

jat | 20 marts 2013

@Captain_Zap - wires in the wall vs wires in an extension cord are no different as long as they are of sufficient size for the current. Theoretically, you could use TDR (time domain reflectometry) to see the slight impedance mismatch at the plug and tell there were two plugs, but it would be extremely hard to distinguish that from a splice in the house's wiring.

Instead, I am sure all the car and/or Mobile Connector cares about is that the voltage is in range and perhaps measures the voltage drop as the current changes, so it could detect that your wiring was insufficient for the current, but even that is a stretch.

Many people use extension cords insufficiently sized for the current, and the car carries a continuous load so heat has a chance to build up. Even running my leaf blower for half an hour, an extension cord rated for 15A gets pretty warm.

Hills | 20 marts 2013

I own, and tested the very exact extension cord cited in your post. It works fine. Charges fine. No problems.

This exact extension cord has been posted many times on this forum, no problems reported.

olanmills | 25 marts 2013

Yeah, it might work, but there's no way that you need 240 of them.

nickjhowe | 29 marts 2013

@Jat - TDR - wow. That takes me back. Running 10-base-2 cable back in the good ol' days.

aaronw2 | 29 marts 2013

I made my own 30A NEMA 14-30 extension cord using parts picked up at my local ACE hardware store. Since the wire is rated at 30A I have had no problems charging. I would have to back into my garage as well in order to reach my outlet but the 20' extension cord is working like a champ.

The only issue I had was I went to a friend's house and all of their 220 outlets were NEMA 14-30L and Tesla doesn't offer any L adapters. I may need to make one, though I found some on Amazon that go from a 14-L30 to 14-50.

nvjx | 29 marts 2013

shop | MARCH 20, 2013
I bought the 30' one and used it as a test to test a dryer plug (240v, 30a). It worked fine. Tesla can only tell if you are using an extension cord if it senses a large enough voltage drop when it ramps up the current. And that will only happen if you use an undersized extension cord. Those rv extension cords are sized correctly for 50 amps, so no problem.

shop, how did you get the 30a dryer plug to fit into this Nema 14-50 cord? I'll appreciate it if you could elaborate. Thanks.

shop | 29 marts 2013

@nvjx, I made myself an adapter. It was a fun little project and I actually used a couple of the adapters I made on a recent trip. I made the following document that you can use to make your own adapters until Tesla makes more of them available.


f-tal | 30 marts 2013

I use the 30' camco RV cord every night with my Tesla, my plug is 25' from my driveway. No problems, works fine.

nvjx | 30 marts 2013

Thanks shop.

JackB | 1 april 2013

I have a custom 50' 14-30 extention cord using 4-wire 8-guage outdoor cord (you can sometimes find it at Home Depot for a few dollars a foot); never any problem charging at 24A from electric dryer outlets. Also have a 100' 120V 12-guage extension cord that I've dropped out of hotel windows to hold a charge overnight in cold weather. It usually works okay at 12A, but in some situations I've had to reduce the current to 10A or 8A to keep the car from shutting off due to low voltage.


harryjsommer | 2 april 2013

The last time I was at the local tesla store (dania beach, fl), they were using extension cords to charge their cars. If it's good enough for them.....

Brian H | 2 april 2013

All depends on the gauge and quality. Jack, the low voltage shows the cord is over-stressed. Such stresses can produce cumulative damage, then overheating, then fires. Caution.

Chuck Lusin | 2 april 2013

Great guide Shop!

gimp_dad | 2 april 2013

Personally I would not use a 12-guage 100' cord for 12A, 120V. You need 10-guage for that.

illioilli | 2 april 2013

@Shop: Thanks for the detailed guide, great job!

gimp_dad | 2 april 2013

Shop, your adapters look to be excellent quality. I don't think mine look as good but for those who are building up a set for the first time they might want to consider 6-50 as their main target for their UMC plug. It avoids messing with the 14-50 neutral and allows for a bit lighter extension cord (a NEMA 6-50 welders' cord only has three conductors instead of the four found in a 14-50 cord).

Because I was lucky enough to talk Tesla out of both 6-50 and 14-50 adapters back in Aug when I took delivery, I had the choice of which type of extension cord to choose and hence what type of adapters to make. I settled on 6-50 for the above reasons.

And, as many have already mentioned, be paranoid if you make any of these adapters. Some of them can be dangerous even if you wired them up exactly as described.

Hills | 2 april 2013

Tesla will not offer the adapters Shop made, as Tesla does not want the liabilities. For those who want the extra length, the only choice is to make your own.

kashiraja | 2 april 2013

Should be no problem as long as the gauge of the cable is close to the same as what you have in the wall (e.g. #8 for 14-50). Of course the cables have ratings so that should be sufficient to consider. The thinner the copper, the more voltage drop you get and the more heat will radiate from the extension cord and won't be charging your MS. The longer you run a cable the thicker the copper should be also.

gimp_dad | 2 april 2013

@Hills not sure who you are responding to but I was pointing out the option I chose which was to make the adapters Shop made but with the "other" end being 6-50 rather than 14-50. I have pigtail adapters for
10-50 to 6-50
10-30 to 6-50
L14-30 to 6-50
14-30 to 6-50
14-50 to 6-50
6-20 to 6-50

Thus, given any outlet that I list on the left side of the above list, I can connect through my 50' welders' extension cord to my UMC. The welders' cord is made with 8-guage wire and one less conductor helps its size and weight.

gimp_dad | 2 april 2013

Also, Tesla has already started offering the 10-30 adapter for the UMC which is one of the "controversial" ones since it is effectively tying neutral on the outlet to ground on the car end.

The issue is that you don't want to carry a whole stack of extension cords with you for that rare case where you are stuck and need to charge from some outlet that you can't get close to. The pigtails plus extension cord solve that problem.

DouglasR | 4 april 2013


Is there a reason why you didn't build a 5-15 to 6-50 pigtail adapter? I'm thinking of picking up an extension cord to use with the supplied NEMA 5-15 adapter (I'm heading in the next few days to a resort cabin that has an outdoor 110v outlet). I was hoping I might be able to get a heavier cord that could then also be plugged into a 240v outlet, using an adapter? For example, could I get an RV or welder extension cord, and then buy or build an adapter to use that cord with a 110 outlet.

On the other hand, since I haven't seen such an adapter for sale and I don't think I could build one before I leave, I'll probably just get a 110v cord.

shop | 4 april 2013

@gimp_dad, yeah, that makes a lot of sense to use the 6-50 instead of the 14-50 as your base adapter. Just didn't think of it.

shop | 4 april 2013

The trick is to find a nice receptacle for the 6-50. Because they need to look nice :-)

shop | 4 april 2013

Oh, but thinking about it, I don't know if the 6-50 adapter into the tesla would accept a 120v adapter. I notice that gimp_dad's adapter set does not have a 120v one. You would have to test it out. Also, of course, the 14-50 comes with the car, and you'd have to purchase a 6-50 adapter from tesla...

DouglasR | 4 april 2013

@shop - yes, that was my concern. I had assumed, looking at gimp_dad's list, that the 6-20 adapter was 120 V (because it's 20 amps), but I just looked it up, and it is rated for 250 V maximum. So if the car sees a 240 V connection, it probably won't work to plug into a 120 V outlet, even if you dial back the amps. I was hoping to carry only a single extension cord, but that's probably not possible.

shop | 4 april 2013

Actually you can just use one extension cord if you make a 5-15 adapter (regular household plug). I've got my bulky 30' nema 14-50 extension cord plug the mobile charger 20' cord equals 50' reach. Again I know this works if you use the 14-50 as the base adapter, and frankly it should work with the 6-50 too, you just have to test it since I haven't seen anyone on these forums say it work with 120v.

DouglasR | 4 april 2013

OK, I see from your document that you did make a 120 V adapter for your 14-50 cord -- it's a NEMA 5-20. Any you say you haven't tried it out yet?

shop | 4 april 2013

I have tried it out - the nema 5-20 and 5-15 work just fine, as does the TT-30 (also a 120V source). I said I haven't tried these out on a NEMA 6-50 Tesla plug instead of the NEMA 14-50 that I used.

gimp_dad | 4 april 2013

@DouglasR and shop

Haven't considered making a 5-15 to 6-50 adapter but I assume it would behave then same as a 5-15 to 14-50 as I am pretty sure the Model S adapter delivers the same three conductors to the charger plug in both 14-50 and 6-50 UMC adapters (ignoring neutral with the 14-50).

Does your 14-50 to 5-15 work? I assume you are connecting hot to hot and neutral to the other hot and ground to ground. I may try it out. I will send a picture later but am pretty happy with the 6-50 receiver I used. Seems solid and has good connections both mechanically and electrically. I will send a picture next chance I get.

shop | 4 april 2013

Yes my 14-50 to 5-15 works. The UMC is picky, however, as to which hot the 120v hot goes to and which one gets the neutral. My document describes how to wire it for a 14-50, and my guess would be you would use the same polarity for the 6-50. The other useful 120v adapters are a tt-30 ( for a derated 24amps), and a 5-20 which you do find in commercial garages from time to time. You can of course just plug a 5-15 adapter into a 5-20 socket, but then you would be pulling slightly more amps than what the plug is rated for.

Btw, the one time I used my TT-30 adapter, I was only able to draw 20amps from it. Couldn't make it draw 24amps. I suspect that is an artificial software or hardware limitation in the UMC - they probably didn't envision a 120v source that was capable of delivering more than 20amps.

JackB | 10 april 2013

I'd argue there's no problem using a 100-foot 12-gauge extension cord to charge at 120V 12A. It's the same wire gauge that's most commonly used to connect the wall outlet to the breaker panel. It has 1.6 ohms of resistance per 1000' feet, so unless the total run from the breaker panel to the car exceeds 350 feet, you'll still see at least 113V, which works (if you don't like it, you can always cut the current to 6A and the voltage will rise to 116-117V). Finally, there's no increased risk of fire hazard with the extension cord in that situation, because the heat generated per foot of wire is about a quarter watt - no different than what happens to the wire between the panel and the outlet when you plug in a hair dryer and run it on high.


DouglasR | 10 april 2013

@Jack, on your long trip, did you have any occasion to use a 100' cord? It's a lot to lug around, and I'm thinking 50' (+the UMC) ought to be long enough for most any occasion.

cathy | 14 april 2013

Am I going to be okay to plug my Tesla 14 50 adapter into a Camco 30' 50 amp cord and then use a 14 50 to 14 30 adapter on the other end to plug into a dryer receptacle? I would first dial the car back to a 24 amp charge.

Is there a power loss when two adapters are involved like that on each end of an extension cord?

nickjhowe | 14 april 2013

@cathy - your setup is exactly what I created. I tested it with a 10-30 connector and it worked with no measurable loss.

shop | 14 april 2013

Cathy - that should work fine. Dialing back amperage to 24 amps should be all that is needed.

Brian H | 14 april 2013

And the car should remember the amperage setting by location. So you should only have to dial back once. IIRC

DJay | 15 april 2013


"Am I going to be okay to plug my Tesla 14 50 adapter into a Camco 30' 50 amp cord and then use a 14 50 to 14 30 adapter on the other end to plug into a dryer receptacle?"

I would like to do this as well, I have not been able to locate 14 50 to 14 30 adapter, have you?

jat | 15 april 2013

@DJay - most of the people who are doing this have made their own 14-50R => 14-30P/10-30P adapters. It isn't hard if you know what you are doing.

DJay | 15 april 2013

jat- Thanks for the follow up. I was just reading the great instructions published by "shop" earlier in this thread and will give it a try. It certainly looks easy enough.

zain.saidin | 19 maj 2013

Boy... Think how much easier this would all be if Tesla sold a much longer version of the UMC... You know, like one that might actually reach a dryer outlet from a driveway? Then we wouldn't be buying/fabricating adapters to go to extension cords to connect to their tesla adapters.

Has anybody just spliced in a 50' extension to the UMC cable itself? Yes, I know, some voltage drop. But like several above have noted, use the right gauge wire and this can be minimized. Charge with a little less current if you have to. It just seems like an spliced-in-extension between the module and the adapter that takes all the different tesla plug heads would be less hassle than a 14-50 extension cord plus a bunch more adapters for THAT.

riceuguy | 19 maj 2013

@Zain, that seems a bit crazy given the reported successes with

shop | 19 maj 2013

If you are going to the trouble of splicing a cord, then installing a closer 240V receptacle isn't that much more work. I'm not even sure HOW to splice a cord that carries 50 amps/240V. That is a DIY job I would not want to do. The home made adapters may look like a lot of work, but they aren't really. And when done right, you aren't going to be wondering if the cord/receptacle/adapter is going to catch fire.

Yes, Tesla could sell a 50' UMC, and that might be nice (or not, see below).

In the meantime, the home made adapters work fine, and you get the added bonus of being to plug into all sorts of power sources should you get into a tight spot, or even a routine spot. People have charged from work using a TT-30, for example. Or from a marina using an SS-50 50A connection.

The reality is that electric cars need relatively close by power sources. Stringing 50' of 240V/50A power through a house might be fine for occasional use, but if you think about it, it isn't very safe. It is a trip hazard. Accidentally yanking such a cord so that the plug comes partially out of a socket isn't likely to be very safe.

zain.saidin | 20 maj 2013

Thanks Shop.. I think, that splice can be done. Though there's a lot to do to make sure it's right. And I do worry it'd be more work the what you did.

It wouldn't be for regular use, obliviously if you go to that kind of trouble you might as well put the outlet or high power wall charger where you need it I the garage. Which we did.

But for road trips and taking the car out at the edges of the charging network, I'm looking for the handiest solution that can be tossed in my "frunk." One that'll let me use various dryer outlets, RV camp outlets and the occasional twist lock style one you encounter. I started down the path you already tread with your excellent note on buying and making adapters. But then thought: you know, if this stupid cord was just longer, then I could use the tesla provided adapters, not carry an extension cord and not have a box of extra adapters.

I get the safety thing. But if it's going to be a moble adapter, then it does need to work in moble situations. There isn't always a nice wide parking stall a short distance from the outlet you want. Even stopping in with the in-laws you have the driveway to dryer scenario. Pulling into an RV area and borrowing shore power you'd need even longer.

lnxcar | 20 maj 2013

I got a camco 15' and 30' and chained them together and gave that a try and it works perfectly fine, it charges at full 40A (per the webservices read-out)
like 237V/39 or 237V/40 readings. zero issues. if anyone needs an easy way to extend the reach, these cords do the job well.

mdemetri | 4 juni 2013

Does anyone know if the adaptors sold by EVSEadapters (link below)will work (link below)? They appear to be similar to the homemade ones by shop but they use a 10 gauge cable for the NEMA 14-50 to NEMA 14-30 connector, wheras shop used 4 wire. Is this a problem?