Reader Questions, Answered: Should I Use an Extension Cord With an Electric Car?

Here at Transport Evolved, we spend most of our time bringing you the latest news in the world of cleaner, greener, safer and smarter transportation. Sometimes, that means covering the latest press releases from major automakers. Sometimes, it means taking cars out for long test-drives to put them through their paces. And sometimes, it means answering reader questions.

Can you or should you use an extension lead to charge an electric car?

Can you or should you use an extension lead to charge an electric car?

Today, we’ve been sent the following question by Phil, who is about to test out a Nissan LEAF for a few days to see if it’s a good match for him and his family.

He writes:

I’m after some advice on the use of an extension lead to charge a car.  I’m getting a Nissan Leaf on a 7 day trial and have no driveway, so would have to use an extension lead to charge it.
I have seen Robert Llewellyn and some other people use one in videos, but for my trial it says not to use one.

It wouldn’t be an ordinary extension lead I would use, it is one I use when I go camping, and I have an adaptor to plug it into a mains socket, so with all the extra safety features of the extension, what do you think?

Thanks for your question, Phil. It’s one which we’ve been asked before, so we hope you won’t mind if we turn this into a little piece of advice for other would-be plug-in owners who are asking the same question. In fact, charging with extension cords is one of the more common questions we’re asked, so we think it’s high time we offer our advice.

Why its ‘officially’ not recommended

To start, it’s probably best to examine why most automakers advice against using extension leads when charging a car, and why many even discourage the use of a portable charging ‘brick’ or Electric Vehicle Supply Equipment (EVSE) instead of a dedicated charging station.

It’s common sense that an low to medium-power electric car charging station — portable or fixed — takes power from the mains electricity at either 110 volts or 230 volts, and feeds it into the charging inlet of your car. The type of fixed, permanent charging stations sold for home use are traditionally capable of between 3 kilowatts and 10 kilowatts of power transfer, depending on the type of charging station and the car you’re wanting to charge. Portable charging stations usually provide between 1.5 kilowatts and 2.8 kilowatts, depending on the country you live in.

In pretty much every country we can think of, charging stations which are permanently wired into a building’s electronics are supposed to be installed and checked by a qualified electrician. In some places, those installations must also be certified as being both safe and up to appropriate  wiring regulations or code. These checks not only check the quality of the installation, but also ensure that the electrical circuit feeding the charging station is appropriately rated for the amount of power the charging station and car will require.


This is the reason why automakers don't like you using portable charging equipment in untested outlets.

This is the reason why automakers don’t like you using portable charging equipment in untested outlets.

When it comes to a portable charging station however, the unit can be plugged into any power outlet, regardless of its age or condition. In the UK, where Phil is writing from, this means a household outlet which is rated at 230 volts and 13 amps. We should note however that most portable charging units pull between 6 and 10 amps to give at least minimal headroom between the maximum current drawn and the maximum theoretical current the outlet can provide.

Assuming the wall outlet the portable EVSE is plugged into is correctly wired, has the correct power rating and has clean, no-corroded contacts, charging your car from it will have no problem.

But if the contacts are corroded or poorly maintained, the cable joining the socket to the fusebox is of an incorrect rating, or there’s some other lose connection somewhere between fuse box and EVSE, it makes it harder for electricity to pass through the circuit. When that happens, the cables and connectors can heat up.

Since it’s likely that most domestic outlets are correctly maintained and appropriately wired, automakers generally consider it okay to charge up from a wall socket in an emergency, since they can vouch for the condition of the charging cable and EVSE ‘brick’.

Include an extension cord of unknown origin, specification and condition, and most automakers get a little nervous. That’s because you’re not only adding an extra pair of connections to the circuit — which increases the risk of a poor connection somewhere — but you’re physically making the electrical circuit longer. The longer the physical circuit, the more likely it is that the electricity will find it harder to flow along the cable.

What’s more, most extension leads aren’t meant to work with the heavy, sustained loads called for when charging an electric car, and can easily heat up when pushed too hard.

When there's a problem with a circuit, be it mechanical or electrical, there's a risk of a fire or overheating.

When there’s a problem with a circuit, be it mechanical or electrical, there’s a risk of a fire or overheating.

To avoid any unexpected problems, most automakers — especially when carrying out extended test drives — request people don’t use extension cords.

Reality is sometimes different

You’ll note we split the nitty-gritty explanation into its own part, and that’s because as is often the case with life, the reality of using extension cords is somewhat different.

Of those we know with plug-in cars, most carry some form of emergency extension cord with them on longer trips or when visiting friends and family who don’t have a dedicated charging station. Instead of being a cable they’ve found in the back of the garage, these owners will take their time and buy a cable which is approved and rated for use on higher electrical loads.

This is an example of a poorly-built charging lead.

This is an example of a poorly-built charging lead.

In the UK, where it’s okay to still wire your own extension leads, some owners even make their own heavy-duty extension cords, buying appropriate heavy-duty 13-amp sockets and flexible, heavy-duty ‘Arctic’ cable that is rated to carry an electrical load far higher than the EVSE will pull.

In these cases, the use of an extension cord isn’t all that risky — although we should note there is always some inherent risk in adding extra physical connections in the circuit — and when used apporpriately with a well-maintained, tested power outlet, there shouldn’t be a problem.

Phil’s situation

In Phil’s case, we note that the cable he’s proposing to use is one which is rated to carry far more than the current the portable EVSE will use , and even makes use of the CE 16-amp (blue) plug found at camp sites across Europe on one end. As well as being a larger connector — which lowers mechanical and electrical stresses on the plug and socket — the cable itself is rated to carry 25 amps, far more current than the EVSE will pull.

If used correctly, extension cables shouldn't pose a threat.

If used correctly, extension cables shouldn’t pose a threat.

If someone were to use this extension cord to charge an electric car, it would be one of the better extension cords we’ve ever seen used for the purpose. Here at Transport Evolved, all of our plug-in owning staff have used extension cords from time to time to charge a plug-in car. And for the most part, we’ve not had any problems. But we also know people who have been unlucky through using an unfamiliar outlet, or whose portable EVSE  has pulled out of the attached plug, causing an electrical short and heating. As a consequence, you should NEVER use a portable charging unit with an unknown power outlet or an unknown extension cord, and you should only really use portable charging units as a temporary or emergency solution in preference to a dedicated charging station.

DISCLAIMER: We’re not condoning the use of extension cords to charge your plug-in car. Nor are we saying bad things will happen if you do. We’re saying that yes, there are risks and yes, when used with the correct precautions, you shouldn’t have a problem.

Transport Evolved accepts no responsibility or liability for those who choose to use an extension cord after reading this discussion. Instead, the onus is on each individual to accept all liability when using a portable EVSE — with or without an extension lead. 


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  • Surya

    Excellent article.nnI’ve always made sure that the extensions or convertion plugs I’ve used are rated 16 amps or more, above the 10 amps the granny cable for the ZOE uses. So far so good.

  • James ElectroGeek Killick

    I used an extension cord with the standard UK indoor 3 pin 13A plug for quite some time. I was feeding around 10A constantly for an hour or so then then charge reduced somewhat as the cycle progressed. I had a bad connection on the wall socket at the actual pins and that resulted in a plug and socket just like the ones in the photos here. I put a new plug on and used a different socket and all was well again. I then got the 16A caravan type socket installed just outside my garage door (which as more convenient). I always use a properly rated extension cord with the caravan connectors. I once had a connection issue with the caravan type plug and it tripped out the supply (at work actually). There was no burning apart from a bit of crispiness on the end of the cable. I cut a few inches of wire of and rewired it and all was well again. So my experience is the 13A plugs and sockets are not such a good option for using extension cords and the caravan type are much safer and less likely to fail. When the caravan type fail they generally result in just a lost of power and maybe a small amount of arcing before that because of the circular pins making a better contact. I had to get a special cable as we had type 2 posts put in at work and my car only has the caravan connector type. Occassionaly I cannot get right on the post and have to add an extension cable and this has always worked fine. I also had a proper EV type 2 charger installed at home as part of the government scheme for free. I use this with my special cable and an extension cord all the time and never had an issue. I am a qualified electrical engineer and currently work in vehicle research and development, so I am well qualified to advise almost exactly the same as the team here. Make sure you know what you are plugging into and what cable you are using. I try to avaoid using the 13A 3 pin plugs as they are generally a lower quality than the 16A caravan types. Dedicated EV chargers are for sure the best option as you can be sure the installation was checked and the cables are normally well made. http://www.probatron.blogspot.comnJames

  • Paul Churchley

    I have heard many people say that they have charged using a portable EVSE and extensions without trouble and I am sure that is the case. However, get it wrong and it could be serious.nnI charged at my sister’s house using a standard 10A EVSE and an extension… the cable itself got very warm (yes, it was unwound 🙂 ) and the socket into which it was plugged was also warm. I stopped the charge after an hour and charged at a local public charge station… lucky there was one close by.nnSo yes, you can do it safely but only if the wiring and sockets are all in good condition and the correct rated cables are used (10A CONTINUOUS).nnJust be cautious everyone… this is not like plugging in a kettle!

  • Petaltown

    My daughter-in-law just bought a Fiat. She lives about 35 miles away. Yesterday she wanted to find a charging station up here, but it turns out the Fiat plug doesn’t fit the socket at the public charging stations. We took it to my house and plugged it into a regular household extension cord. My house was built in 1927 and the wiring has had some upgrades but some of those were DIY. We left it and came back after 2-3 hours. The plug was very very hot. Her car said it was good for 40 miles. I guess the best suggestion is for her to carry a high quality extension cord with her from now on.

  • Ormond Otvos

    You could have talked about wire size, a small shot of WD40 and several insertions of the plug to reduce corrosion resistance, and USA 15 and 20 amp 117 volt male plugs also. A fifty foot 12/3 cord with good new 20 amp ends is my choice. PlugShare has a smartphone app that informs one of private residences and shops that have 117 volt outlets available, in real time. I’m in the SF Bay Area, driving a Soul EV. I wired a 20 amp 10/3 cord 12 feet long direct to the 20 amp breaker to get to the car, using the factory EVSE with its 25′ cord. Seems to have sped up the charging rate about 10%, which saves 2 hours.

    • Christopher Williams

      I know this is a year ago, but, I worry about you spraying WD40 in your electrical sockets. If there were to be any spark caused by improper contact then the WD40 would ensure you have a decent conflagration as it is highly flammable. Says so on the can too.
      Don’t mean to offend.
      Have a good evening.