Last week, when a British public safety group noted that up to 75 percent of plug-in car owners there had used an extension cord to plug in their cars, we thought the problem was likely more prevalent in Britain and other European countries with 230-volt standard electrical service than it would be here in the U.S.
So in last week's Twitter poll we asked our readers, a majority of whom drive electric cars and live in the U.S., how many of them have used an extension cord to plug in.
The results surprised us, with 61 percent admitting they've done it at least once or twice. That runs counter to warnings from all automakers, charger manufacturers, and the U.S. electrical standards never to use an extension cord to plug in an electric car.
The problem is a safety concern that the cord could overheat if it can't handle the load, and none of these organizations want the liability for that, should you burn your house down. Although gasoline is hardly immune to fires, at least when you fill up a car with gasoline, you're likely to be awake, standing next to the car, and able to react should anything go wrong—not sound asleep upstairs with your family.
As many of our readers pointed out, however, that may be an overly simplistic view of the situation. Some heavy-duty extension cords are rated up to 30 amps and can handle the basic loads for charging an EV at Level 1 (110 volts.)
The problem is, they're not as common as the 15-amp or 20-amp cords that could be a problem. Also, since voltage drops over the length of any wire or cord, approving a simple amperage rating won't suffice; a shorter cord may be OK, while a longer one could overheat. Automakers don't want to get into the business of rating or approving individual extension cords for their plug-in cars, so they avoid the issue by insisting that cars only be charged with the charge cords they come with.
Have you ever used an extension cord to plug in your car?— Green Car Reports (@GreenCarReports) June 3, 2019
Only 39 percent said they have never used an extension cord to plug in, because it's too risky. Another 16 percent said they have once or twice, and 19 percent said they do "occasionally." More than a quarter, 26 percent, said they use an extension cord "Every day, Is that bad?"
The other thing automaker restrictions don't address is the fact that under the SAE J1772 charging standard, computers in the cars and their native cord-sets should be able to detect whether they're plugged into an extension cord and whether it's overheating, and shut down the charge session if it is. (Ford even recalled thousands of charge cords when they lacked the sensor to do this.)
We don't recommend or condone using an extension cord for charging. But for the majority of our readers who have, make sure to read all relevant specs to make sure the specific cord you're using is capable of handling the amperage your car needs.
And like our electrical advice, remember that our Twitter polls are unscientific because of low sample size and because our respondents are self-selected.