Ac Receptacle

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  #1  
Old 04-27-05, 12:22 PM
davisk43
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Ac Receptacle

I have a very old wall sleave AC Unit. The plug for the old looks to be a 20-amp grounded receptacle (not the normal receptacle, the hot and neutral are vertical) with a T-shaped neutral slot; it is using two 20-amp breakers (which are strapped together). The receptacle is wired by a red (silver terminal screw) and a black (brass), no white or ground????? I wanted to just replace this with a 20AMP receptacle, the common type, because the AC Unit only requires a regular 15AMP receptacle. What gives????
 
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  #2  
Old 04-27-05, 01:23 PM
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You need to do a better job describing the plug (at the end of the cord) and the receptacle (in the wall). I am having a hard time understanding what you are trying to say.

A 120 volt 15 amp receptacle has two vertical slots for the hot and neutral and a D shaped hole for the ground. A 120 volt 20 amp receptacle has a T shaped neutral but is otherwise the same as the 15 amp receptacle.

240 volt receptacles are different. 15 amp versions have the hot and neutral horizontal, while the 20 amp has a T shaped neutral.

The various plugs are designed to fit these receptacles, with a 15 amp plug fitting either a 15 amp or 20 amp receptacle, and a 20 amp plug fitting only it's 20 amp receptacle.

It sounds like you have a 120 volt receptacle wired for 240 volts. However, I cannot be sure.

Please describe the receptacle in the wall, the plug on the old unit and the plug on the new unit.
 

Last edited by racraft; 04-27-05 at 01:40 PM.
  #3  
Old 04-27-05, 05:30 PM
davisk43
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Sorry, I guess I took it for granted that when I said the hot and neutral were vertical, it would be obvious that it's not the common receptacle ( = D ). From your reply and some web surfing, I am positive the current receptacle is 20 AMP/240 VOLT receptacle. That is, the current receptacle looks similiar to the below pic:

l
D
l-

The plug on the old unit fits the above receptacle.

The new AC plug is your commom plug ( = D ), fits into the common 15AMP receptacle. The current wire is 12AWG, and there is one red (connected to the silver terminal screw) and one black wire (connected to the brass terminal screw). No white, this is something I have never seen before? Aren't Red and Black usually reserved for hot wires??? Anyway, can I change the old 20A/240V to a 20AMP/120V receptacle or do I need to change the circuit as well? Any other alternatives?

BTW ...Thanks for your time and response!
 
  #4  
Old 04-28-05, 12:32 AM
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You are describing a 240 volt 20 amp receptacle. This will not work with your 120 volt 15 amp air conditioner.

My first advice is to get a different air conditioner. A 240 volt air conditioner will work better than a 120 volt model. However, you still have the problem of no ground wire.

If that is out of the question then you could replace the current receptacle, however you will need to run new wiring as you have no neutral wire and no ground wire. If you are uncomfortable running new wire and connecting up a new receptacle then you will have to bring in an electrician.


One final thought. If the wires are run in conduit then you can probably run new wires with minimal effort.
 
  #5  
Old 05-12-05, 09:24 PM
davisk43
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Thanks again...One more question about running the new wire. (I don't see any way around it since I am missing a ground) If I only need a 15 AMP circuit and the AC unit is independently ran off of the two locked 20AMP ckts, which I believe creates the 240 VOLTS. Can I eliminate one of the 20AMP Ckts, run a new ground wire off the netreul bus bar and one hot from the remaining 20AMP ckt, and just pitch the other?? Is it OK to have the AC on a 20 AMP/120 Volt Receptacle even though it only requires the 15??
 
  #6  
Old 05-13-05, 08:49 AM
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Originally Posted by davisk43
Thanks again...One more question about running the new wire. (I don't see any way around it since I am missing a ground) If I only need a 15 AMP circuit and the AC unit is independently ran off of the two locked 20AMP ckts, which I believe creates the 240 VOLTS. Can I eliminate one of the 20AMP Ckts, run a new ground wire off the netreul bus bar and one hot from the remaining 20AMP ckt, and just pitch the other?? Is it OK to have the AC on a 20 AMP/120 Volt Receptacle even though it only requires the 15??
There is no problem running a 15 amp A/C on a 20 amp circuit. However, if this circuit has exactly one outlet, which it probably will, you need to make sure the outlet is of the 20 amp type if it has a 20 amp breaker. The code requires this for single outlet circuits to ensure that people do not attempt to put 15 amp plugs on 20 amp appliances. This will not be a problem for a 15 amp A/C since the 20 amp outlets also work with 15 amp plugs (but since the A/C won't be using more than 15 amps, you're OK).

Replacing the double breaker with a single breaker will take you from 240 volts (line to line voltage) to just 120 volts (line to neutral voltage).

You could just change everything to a 15 amp circuit (15 amp breaker, AWG 14 wire, 15 amp outlet) since you are re-doing it all. But if it were me, I'd do it at 20 amp (20 amp breaker, AWG 12 wire, 20 amp outlet compatible with 15 amp) since it is legal, safe, and won't need more upgrade if the A/C is upgraded to a 20 amp model.

The wire you get will be a cable consisting of 3 conductors total. The hot will be insulated black. The neutral will be insulated white. The ground will be insulated green (generally only in metallic armored cable) or left bare (in non-metallic armored cable).

If this A/C is located in a bedroom, and your location has adopted the recent NEC (I believe starting in 2002), you may need to use an arc-fault circuit breaker. This rule only applies to 120 volt circuits (not 240 volt circuits). The arc-fault breakers do add safety, but some appliances like air conditioners may trigger nuisance trips. Call your local electrical inspector's office and ask. This is one of the reason I personally prefer to use 240 volt air conditioners; in case the AFCI causes problems with it, I can change to a normal breaker and still be in compliance.

If at some point in the future you need to switch back to 240 volts, you can just keep the same wire in place. You'd put back the double breaker, remark the white wire with red or blue on both ends (a few inches of appropriately colored tape well wrapped around it) and move it from the neutral to the other end of the double breaker, and change the outlet to the 240 volt type. Virtually all 240 volt appliances in the 15 and 20 amp range do not use a neutral wire for anything (30 amp dryers and 40 or 50 amp ranges are a totally different story).
 
  #7  
Old 05-13-05, 03:31 PM
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davisk,

I suspect that you left something important out of your description. You say that you have a red wire, a black wire, and no ground. But I don't think you told anyone about how these wires run between your panel and your receptacle. Given that most all _cables_ would have a black wire and a _white_ wire, and that you are in _Chicago_, I am guessing that your wiring is run in _conduit_.

If this is the case, then the conduit itself can act as the ground. It is always _better_ to run a ground wire, but the conduit will be an acceptable ground fault return path.

Your comment about red and black being associated with 'hot' wires is correct. A 240V circuit has _2_ hot wires.

-Jon
 
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