TL;DR: Is it fine to use 10' 12/3 extension cord or should I really have an electrician come out & install a new outlet?

I recently installed 8,000 BTU window air conditioner (the LG LW8016ER). Unfortunately, there isn't an outlet near the window.

I've heard lots of disclaimers that you should have an electrician come out to install a new outlet, and not use an extension cord. Is that really necessary if I get an extension cord of sufficient gauge? Specifically a 10' 12/3 SJTW (the Thonapa TH-123Y10).

Reading around, most of the wiring used to connect the outlet is 12 gauge as well, so it didn't seem like it would that different from just running the extension cable.

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    I only see that extension cord on Amazon, eBay and foreign sites. That is usually a strong warning of cheap Cheese junk. Huge amounts of sub-par electrical trash are dumped on these shores, and you must be way of it. Look for a listing and file number from UL, CSA, ETL, or other competent testing lab. That one has a UL stamp, but it might be faked. Buying in-store at local mainstream retailers (not flea market type operations) is usually safe. Sep 1, 2019 at 19:29
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    I think a lot of the manufacturer talk about 'no extension cords' is a lot of CYA from the lawyers because ordinary people don't understand length and gauge requirements for high draw appliances. You, on the other hand, understand both, so I'd suggest you go for it. Make sure you get a high quality cord, per @Harper, and make sure it doesn't get jostled half-in-half-out over time by something like a vacuum. Sep 2, 2019 at 18:27

3 Answers 3


Extension cords are fine, for temporary situations. If you or anyone else are going to be tripping over an extension cord, we all know that's not good... Especially while something's plugged in.

It wouldn't pass an inspection if you were ever going to sell the place.. But bottom line, that is ultimately every individual's choice. I personally would not have extension cords for more than a weeks period of time.. While the safer outlet was getting installed, of course.

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    Thanks! Is tripping the main concern? The extension cord would be out of the way, along the wall in my den. We're planning to remodel in a few years (and get central AC then), and really only need to run the unit a few months out the year. My main worry is the threat of fire or something similar life-threatening.
    – Bill
    Sep 1, 2019 at 18:40
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    Extension cords are a tripping hazard. Moved out of the way, is always the preferred way to run them. But by their very nature, they can easily become trip hazards, due to their length. Your cord's ability to handle the current is fine. Good luck sir 👍 on your home improvement projects. Sep 1, 2019 at 21:33

R.E. Has a great litmus test. If you are going to sell, rent or AirBnB the place like this, fit a proper receptacle. Otherwise...

It's about cord damage, and melting extension cords

A lot of Electrical Code and UL rules come from data science.

Most consumer extension cords are intended for, you know, lamps. They are 16-18AWG, good for 7.5-10 amps in ideal conditions, but they often have problems at connector ends. Historicaly A/C units pulled as much as 13 amps (less now, since Energy Star and SEER). As such, it's a high priority for NFPA and UL to discourage extension cord use, because consumers will make bad choices in extension cords.

However, via data science, it has emerged that a large number of casualties happen because of frayed air conditioner cords. This is why air conditioners use funny cords, and have that GFCI-looking thing on their plug. It is actually optimized to detect cord damage. Needless to say, that gadget can't protect an extension cord - so an extension cord defeats its purpose.

Use an extension cord ...carefully

This is me advising going against UL advice and Code, if you are able to take responsibility for the reasons.

Or, use surface conduit

You add a "starter box" at your receptacle, then follow the wall to a suitable location. #12 THHN wire will suffice, presuming it is actually a proper, mains-listed surface conduit system like Legrand Wiremold, and not merely a cord-organizer intended for ethernet and the like.


Also consider that tripping over the wire could cause the unit to become jarred and possibly fall out of the window, perhaps breaking glass or falling on someone depending on how firmly the unit is secured and its location. There's a reason behind the slogan 'safety first'. It is not worth the risk of injuring someone, perhaps a child--just to save a few bucks.

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    I'd argue that if a solid yank on the cord is enough to make the air conditioner fall out of the window, it was never mounted properly in the first place, and isn't safe regardless of how it's plugged in.
    – Nate S.
    Sep 5, 2019 at 17:16
  • Agreed. But, I never under estimate the amount of shortcuts someone in a hurry is willling to take.
    – peinal
    Sep 5, 2019 at 17:31

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