Is it safe to use an extension cord for EV charging?

My neighbor has an electric car. He parks it in his driveway and uses 50 feet [15-metre] Extension cord to charge it from a plug outside the house. Is this safe? I know from using power tools that a wire that is too long can lead to a voltage drop. Could it take longer to ship? Daryl, Kelowna, British Columbia

If you drive an electric car and you can plug it in at home, you pretty much have a gas station in your driveway — as long as the charging cable that came with your car can fit into a wall socket.

Most automakers say, if it can’t, don’t use a regular extension cord to access a 120-volt wall socket.

“Using an extension cord is generally not recommended and a vehicle owner’s manual will certainly warn of it,” said Michael Stanier, a spokesperson for Plug In BC, a Vancouver-based non-profit EV educational program.

For example, page 152 of the Ford Mustang Mach-E owner’s manual says “Never use the charger with an extension cord.”

For charging at home, you can either use a standard 120-volt wall socket – the slowest method for charging, also known as level 1 – or a 240-volt wall socket, the type used in dryers, which is known as level 2.

For Level 1, you connect the vehicle to an adapter—every electric vehicle comes with one—and plug it into a wall outlet.

The problem is that most adapters don’t have long wires.

In a small informal 2019 Twitter poll conducted by Green Car Reports on the EV news site, 61 percent of respondents said they used an extension cord.

So why are extension cords a bad idea? It could overheat or cause a fire, Stanier said. This is especially true if the wire is long or if you are using two wires joined together.

“The longer the wires are or are joined together, the higher the resistance, which means they will heat up more,” Stanier said. “The biggest safety concerns are that the wire could overheat too much, melt a hole in its shield and start a fire or cause a dangerous malfunction that could damage other equipment involved.”

But the charging standard is SAE J1772, a five-pin connection used to charge electric vehicles and PHEVs that automakers are encouraged but not required. To continue, electric vehicles and charging inverters must be able to detect when the vehicle is connected to an extension cord and stop charging if the cord is overheated.

An expanded version?

If you have to use an extension cord to charge your electric vehicle, Stanier said, make sure it’s an external cord that can handle the elements.

It also has to be the correct scale to handle the power drawn by a Level 1 charger without overheating, Stanier said.

For example, consider a wire that can handle at least 30 amps of electrical current. The wire bundle will determine the maximum amount of current it can handle.

However, many electric vehicles and charging adapters allow for Level 1 charging speed to be raised or lowered to match what your wire can handle, Stanier said.

Also, “It should be single wire, not multiple [cords] Chained together, and you should never go over them [30 metres]Stanier said. An extension cord should be used temporarily at most.

If I use a longer extension cord, can it slow down the charging speed? Probably. Stannier said, but not by much. “There is always an efficiency loss when sending electricity through wires, but the loss from using an extension cable will not be noticeable,” Stanier said. “Maybe 1 or 2 per cent.”

While it’s okay to use the extension cord in question—say, if you’re charging at a relative’s house on a trip—if your EV adapter doesn’t reach the plug you charge regularly, you can purchase a J1772 extension cable that will safely extend its reach.

They come in different lengths. For example, a 12-meter cable is listed on Amazon for less than $400.

Do you have a driving question? send it to me globedrive@globeandmail.com And put “driving concerns” in the subject line. Emails that do not contain the correct subject line may not be answered. Canada is a big place, so tell us where you are so we can find an answer for your city and province.

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