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So I'm getting a window unit and I've read online that you should never plug an AC into a power strip or even use an extension cord. My room has no three prong(grounded) outlets, can I plug the AC into an adapter or do I need to pay someone to upgrade the outlet?

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    Asking random people on the internet rather than the local electritian, sounds like a solid plan. Especially when we have no idea how your socket looks like, on in what country you live. – Turbo J Jul 4 '18 at 16:14
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    If you adapter is approved, it should have a maximum rating on it somewhere. Look for 'W', 'A' or 'VA'. – Oldfart Jul 4 '18 at 16:35
  • Do you mind being electrocuted if the air conditioning system develops a fault? If the answer is "yes", then get an electrician in to wire it in properly. – Simon B Jul 4 '18 at 22:56
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    There is nothing wrong with using an extension cord to connect a window a/c unit, if the cord is heavy enough. Modern small units (5000 BTU/h) only pull about 4 A continuously. Just make sure that the connection between the extension cord and the cord for the a/c unit doesn't get pull partially out so the plug heats up. – Jim Stewart Jul 5 '18 at 10:45
  • Although I agree with Jim code has discouraged the use of cords for many years but a proper sized cord will work just fine.+ – Ed Beal Jul 5 '18 at 14:56
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The most important thing to consider is how much current the air conditioner requires and how much current the receptacle can supply. Most USA wall outlets can supply 15 amps. Kitchen counter and bathroom outlets have long been required to supply 20 amps, but probably not at the time before grounded outlets were required. You need to first check the current requirement marked on the AC. If it has a standard 15 amp plug, it should require no more than about 80% of 15 amps, 12 amps or 13 amps. Check the fuse or circuit breaker for the outlet you want to use to determine the maximum current it can supply. Also check what other outlets are on the same fuse or breaker. After plugging in the AC, there may not be much capacity for other things plugged into the same circuit. If the circuit has the capacity, you can connect the AC.

Rather than use an adapter to accommodate the grounded plug, it would be better to install a GFI outlet in place to the old ungrounded outlet. I believe that code still allows that, but the outlet must be marked as ungrounded using the label provided with the outlet. (I checked your profile to determine that we are talking about a USA location.) Better than that but more expensive would be to add a ground wire. An electrician would need to determine how that can be done in an acceptable way.

If the AC does not have a standard grounded plug, it must require more than 13 amps. If it requires no more than 15 amps, it could be connected to the proposed circuit, but code requires that there be no other outlets on the circuit. If it requires more than 15 amps, it requires a higher capacity circuit.

  • GFCI'S do have problems with motor loads, I would change the outlet and run a single ground wire back to the panel this outlet is powered from or at the first 5 feet of the grounding electrode system where it enters the home with an approved clamp. More work but safer having a 3 prong so it won't pull out as easy and now the unit is properly grounded. – Ed Beal Jul 5 '18 at 14:54

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