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Mike G., Master Electrician
Category: Electrical
Satisfied Customers: 7525
Experience:  Proven Professional 48 years Experience
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# How can you tell whether a electrical plug is 220V or 110V

This answer was rated:
How can you tell whether a electrical plug is 220V or 110V for an air conditioner.
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Mike G. : Good afternoon. The orientation of the larger slots. If both are vertical it's 120V. If both are horizontal it's 240V.
Mike G. : The best way to verify is with a voltage tester. Only the guy who installed it knows if he used the right receptacle.
Customer:

I am trying to buy a new air conditioner and this air conditioner is 40 years old and came with the house. We didn't think about this type of thing at that time. Sears, the place where we want to buy the new air conditioner said that we would have to know whether it was 110V or 220V. Are you saying that if it is 120V that we can use the 110V and if it is the 240V that we can use the 220V.

Mike G. :

Correct, the numbers are nominal. One thing to be aware of the circuit you intend to use would have to be dedicated if the A?C draws more than 50% of its rating. I'd check it out first. If it was installed as a dedecated circuit and outlet, you could probably change it to either voltage easily. If it is on a general purpose circuit, if over 50%, you'll have lights dimming and problms with things like TV's if on the same circuit.

Customer:

The plugs I refer to are plugs just for the air conditioners. We have three air conditioners which have one plug dedicated just for each one of the air conditioners. Do we need to contact a electrician to be safe.

Mike G. :

No, you've answered the question - it is dedicated, that's good. Should you want the larger A/C, you could change the receptacle and move the white wire with the black in the panel to a 2 pole breaker. This would give you 240V at the receptacle.

Customer:

Is it advisable to get a converter to be safe. I am not handy with electricity and would not want to do that myself.

Mike G. :

No converter for the purpose. The only way is as I directed, if you want the 240V A/C.

Customer:

I just wanted to know how to tell what air conditioner to buy. I think most air conditioners now are 110V. If that is true and the plug is 220V, would that cause a problem or vice versa.

Mike G. :

The plug will be as required on the appliance. The receptacle will be whatever you have there, unless a modification is required.

Customer:

So a voltage tester will tell me what I need to know about the 220V or 110V as you stated above. I am just trying not to have a fire break out in my house from lack of knowledge on my part.

Mike G. :

I understand. There is no chance of a fire. Whichever A/C you buy will only plug into the right receptacle. From what you said, that the circuit is dedicated, I'm telling you that if it doesn't plug in, then a simple modification will change the voltage available at the receptacle and a device change to the proper receptacle will all that is necessary.

Customer:

Ok. I think I got it. Thanks so much for your help.

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