My neighbour has an electric vehicle. He parks it in his driveway and uses a 50-foot [15-metre] extension cord to charge it from a plug on the outside of the house. Is that safe? I know from using power tools that too long a cord can lead to a drop in voltage. So could it take longer to charge? – Daryl, Kelowna, B.C.
If you drive an EV and can plug it in at home, you’ve pretty much got a gas station in your driveway – as long as the charging cable that comes with your car can reach the wall outlet.
If it can’t, you shouldn’t be using a regular extension cord to reach the 120-volt wall outlet, most automakers say.
“It’s generally not recommended to use an extension cord and the vehicle owner’s manual will surely warn against it,” said Michael Stanyer, a spokesman for Plug In BC, a Vancouver-based not-for-profit EV education program.
For instance, page 152 of the Ford Mustang Mach-E’s owner’s manual says “never use the charger with an extension cord.”
To charge at home, you can either use a standard 120-volt wall outlet – the slowest way to charge, also known as Level 1 – or a 240-volt wall outlet, the kind used for dryers, which is known as Level 2.
For Level 1, you connect the car to an adapter – every EV comes with one – and plug it into a wall outlet.
The trouble is, most adapters don’t have long cords.
In a small, informal 2019 Twitter poll by Green Car Reports an EV news website, 61 per cent of respondents said they’d used an extension cord.
So, why are extension cords a bad idea? They could overheat and potentially even start a fire, Stanyer said. That’s especially true if the cord is long or if you use two cords plugged together.
“As cords get longer or they are linked together, they have increased resistance, meaning they will heat up more,” Stanyer said. “The biggest safety concern is that the cord would overheat, melt a hole in its shielding and start a fire or cause a serious short that would damage the other equipment involved.”
But the SAE J1772 charging standard, a five-pin connection used for charging EVs and PHEVs that automakers are encouraged but not required to follow, says EVs and charging adapters should be able to detect when a car is plugged into an extension cord and stop charging if the cord is overheating.
Extended version?
If you have to use an extension cord to charge your EV, make sure it’s an outdoor cord that can handle the elements, Stanyer said.
“It also needs to be the correct gauge to handle the power drawn by the Level 1 charger without overheating, Stanyer said.
For instance, consider a cord that can handle at least 30 amps of electrical current. The cord’s package will specify the maximum amount of current it can handle.
Still, many EVs and charging adapters allow for the Level 1 charging speed to be turned up or down to match what your cord can handle, Stanyer said.
Also, “it should be one cord, not multiple [cords] chained together, and should never exceed [30 metres],” Stanyer said. “An extension cord should be used temporarily at most.”
If you’re using a longer extension cord, could it slow down your charging speed? Possibly. But not by much, Stanyer said. “There is always an efficiency loss when sending electricity across wires, but the loss from using an extension cable wouldn’t be noticeable,” Stanyer said. “Maybe 1 or 2 per cent.”
While it’s okay to use an extension cord in a pinch – say, if you’re charging at a relative’s house on a trip – if your EV’s adapter doesn’t reach the plug where you charge regularly, you can buy a J1772 extension cable that will safely extend its reach.
They come in various lengths. For instance, a 12-metre cable is listed on Amazon for less than $400.
Have a driving question? Send it to globedrive@globeandmail.com and put ‘Driving Concerns’ in your subject line. Emails without the correct subject line may not be answered. Canada’s a big place, so let us know where you are so we can find the answer for your city and province.