What Should Not Be Plugged Into an Extension Cord?

The short rule: heat and compressors need the wall

An extension cord is a temporary helper. It adds a plug and a bit of wire between the outlet and your device. That extra wire, plus the extra plug connection, adds resistance, and resistance turns into heat.

Most devices draw so little current that the added heat does not matter. Two groups of appliances are different. Heating appliances use a large amount of power the whole time they run. Appliances with a compressor or a big motor pull a surge of current when they start, then cycle on and off all day.

If an appliance does either of those things, the wall outlet is the safe place for its plug. The cord is where problems start, especially a thin one, a long one, or one that is coiled up.

Appliances that should not go on an extension cord

Here are the usual offenders. Always read the label on the appliance too. If the manual says to plug directly into a wall outlet, follow it.

• Space heaters and electric blankets used as heaters
• Toasters, toaster ovens and countertop ovens
• Microwave ovens
• Slow cookers, rice cookers, electric kettles and griddles
• Air fryers and pressure cookers
• Refrigerators and freezers
• Window air conditioners and portable air conditioners
• Hair dryers, curling irons and clothes irons, if you leave them running
• Large power tools and welders that exceed the cord's rating

Why these appliances are a problem

Heating elements are simple: they turn electricity into heat on purpose. That means a steady, high draw for as long as the appliance is on. A cord that feels fine for a lamp can get hot under that load, and a warm cord near rugs, curtains or furniture is a fire risk.

Compressor appliances have a different issue. When a refrigerator or air conditioner kicks on, it briefly draws more current than its running level. A thin cord or a loose connection can drop voltage at that moment. Low voltage is hard on the motor, and the extra heat builds up at the plug.

The cord also has a rating. On our best extension cord page, the 12 AWG cords list 15 A and 1875 W, while the 16 AWG cords list 13 A and 1625 W at most. Add up every device on the cord. If the total goes past the lowest rating on the cord or its plug, you are overloading it.

Can you use an extension cord for a refrigerator or microwave?

For a microwave, the answer is no in normal use. It draws heavy current while it runs, and its manual almost always asks for a dedicated outlet. If the cord on your microwave does not reach, move the microwave or have an electrician add an outlet.

For a refrigerator, the best answer is also no. Food safety makes it tempting, because a fridge runs around the clock. That also means the cord is under load around the clock, and you may not notice a warm plug.

If you have no other choice, such as during a short move or a temporary setup, use the shortest cord you can. Choose a heavy-gauge cord rated for the fridge's amps, which is on its nameplate. In our data, that means a 12 AWG model such as the 25 ft cord with a 15 A rating, not a thin 16 AWG cord. Plug the fridge in alone, keep the cord fully uncoiled, and check the plug for warmth. Treat it as a stopgap and fix it soon.

Choosing a cord for what you can plug in

Plenty of things do belong on a cord: lamps, phone chargers, fans, string lights, a laptop, and many handheld tools used for short periods. The match between load and cord is what counts.

Compare gauge, amps and watts first. Lower AWG numbers mean thicker wire, and thicker wire carries more current with less heat. Length matters too, since longer cords lose more power. You can look at specs side by side on our best extension cord comparison.

The table below shows a few cords from that page so you can see how the numbers differ.

Safe habits for any extension cord

Even a good cord can cause trouble if you use it the wrong way. Follow these steps every time.

Never run a cord under a rug, carpet or furniture, where heat can build up and damage goes unseen. Do not staple or nail it in place, and do not let it run through water or snow. Do not use a cord as permanent wiring. If you need power in a spot all the time, an electrician can add an outlet.

Uncoil the cord fully before use. A coiled cord traps heat, and several listings on our page say to use the cord fully extended. If you store a long cord on a reel, unwind it all the way first. Our best extension cord reel page compares reel options.

• Check the cord and plugs for cracks, bent prongs or scorch marks before each use
• Stop using a cord that feels warm, smells hot or has a damaged jacket
• Use outdoor-rated cords outside and keep plug connections out of puddles
• Do not plug one extension cord or power strip into another
• Look for a lab mark such as ETL on the packaging or spec sheet
• Keep cords out of walkways and away from children and pets

What to do instead

If a big appliance needs power where there is no outlet, the fix is to bring the outlet to the appliance. A licensed electrician can add a grounded outlet, and for some appliances a dedicated circuit. That is the safe long-term answer for refrigerators, freezers, microwaves and air conditioners.

For heaters and cooking appliances, plug straight into the wall and keep the area clear. Also keep a working smoke alarm nearby. If a breaker trips again and again, do not swap in a longer cord. Unplug the appliance and have the circuit checked.

Frequently asked questions

Is a power strip safer than an extension cord for a space heater?

No. A power strip adds another set of connections and is not built for a heater's steady high draw. Plug the heater directly into a wall outlet.

Can I use an extension cord for a window air conditioner?

It is best to avoid it. The compressor needs a strong, steady supply and the cord can overheat. Check the manual, which usually calls for a direct outlet.

Does a heavier cord make it safe to plug in a heater?

A thicker cord is better than a thin one, but many heater and appliance manuals still say to use the wall outlet only. Follow the manual.

What does a cord's gauge number mean?

It is the AWG wire size. A lower number means thicker wire. For example, 12 AWG carries more current than 16 AWG.

How do I know if my cord is overloaded?

Warning signs include a warm or hot cord or plug, a burning smell, discolored plugs, flickering power or a tripping breaker. Unplug everything and stop using that cord.