If you’re just now learning that there are times you should never use an extension cord, consider yourself lucky that you didn’t learn your lesson the hard way. Using an extension cord when you shouldn’t can result in damage to electrical devices and appliances, as well as posing a major safety risk to the user.

Below, we’ve spoken to professional electricians about the six times you should never use an extension cord and why, to take the guesswork out of safely powering your devices and appliances.

Plugging in Major Appliances

Major appliances require a lot of power for operation, including but not limited to the following:

• Microwaves
• Refrigerators
• Dryers
• Air conditioners
• Space heaters

Tim Hodnicki, master electrician at Electrical Experts, explains that this high power draw can overload an extension cord, which may not be rated for the power load. He warns that overloading an extension cord can lead to overheating and even result in fire.

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In Outdoor or Wet Environments

Most standard extension cords are not rated for outdoor use, especially in wet environments. However, just because there’s no rain in the forecast doesn’t mean you’re in the clear, as temperature and UV damage are both a concern.

“Even if they look fine, they can crack or short out,” Ryan Gregor, owner and head electrician at RCG Electrical, says. “I’ve had to replace cords that stopped working after just one season outdoors because they weren’t rated for the weather.”

Hodnicki explains how standard indoor cords are not built to withstand moisture or the temperature fluctuations that can cause insulation to break down. He warns that using an indoor extension cord outdoors can cause electrocution or short-circuiting.

Under a Rug or Carpet

While an extension cord getting hot is a bad sign, it’s not uncommon for an extension cord to get warm to the touch when in use.

Normally, the extension cord’s exposure to open air is enough to dissipate any heat production, preventing the heat from compromising the cord’s integrity. This is why it’s always a bad idea to place an extension cord under a rug or carpet, beneath furniture, inside a wall, or anywhere else that could trap heat and cause the extension cord to overheat.

Additionally, both Gregor and Hodnicki warn that placing an extension cord under a rug, beneath furniture, or behind a wall can cause the insulation to wear down over time, which can result in exposed wiring and pose a fire and shock risk.

Charging an Outdoor Scooter

Charging electric scooters and other electric recreational vehicles is usually more than an extension cord can handle due to the significant power draw.

Just like with appliances that have high power draw, EV chargers can draw more power than an extension cord can safely provide, leading to overheating and fire risk. In some cases, it can even damage the charger.

Over Excessive Distances

If you’re powering something over a distance that requires multiple extension cords plugged into one another, you should find another solution. Extension cords are only designed to safely carry power over their distance.

“Connecting one [extension cord] to another to extend their reach increases resistance and voltage drop, and it’s very easy to exceed the amperage rating,” Hodnicki explains. “I would advise using a single cord of the correct length and gauge for the task or assess whether the job calls for a proper outlet installation instead of a temporary workaround.”

As Permanent Wiring

Extension cords are only intended for brief use and should never be used as permanent power solutions, as they simply aren’t designed for constant use.

“If you find yourself constantly needing extension cords to power everyday devices, that’s a sign your home’s electrical system needs updating,” Hodnicki says.