Need 240 volt receptacle for window A/C

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Old 07-23-15, 08:14 AM
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Need 240 volt receptacle for window A/C

I am considering taking an almost new 230V air conditioner from my deceased parents house and using it where I have a smaller 110V unit where the AC plug is currently 20A 125V. However, I have a very old kitchen range I have been considering replacing with natural gas. The receptacle for the range is a NEMA 10-50R, but the two cartridge fuses are 30A each? If I get rid of the electric range can I reroute the wire [10-3 Romex type in good condition] from the range to the AC location [only a few feet away in an open bay basement ceiling and replace the 115A receptacle with a NEMA 16-6R receptacle without messing with the electrical box? Thank you!
 
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Old 07-23-15, 08:45 AM
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With a few conditions, it sounds reasonable. The cable must have a ground wire. The breaker or fuses needs to match the size required by the A/C unit (probably 15A or 20A). The receptacle you need is probably a 6-15R or 6-20R. I don't see how you could use the existing receptacle box as it already has wiring in it that would need to go somewhere. The best option is to leave the existing receptacle as-is, and install the new 240V receptacle in an old-work box nearby the window.

The cable is wrong for the range anyway -- best to not use it there.
 
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Old 07-23-15, 09:33 AM
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Thanks Ben:

A couple clarifications:

Regarding: The best option is to leave the existing receptacle as-is, and install the new 240V receptacle in an old-work box nearby the window.

I really don't need the existing 20A receptacle; there are more than I need in the room. The existing 20A one was specifically installed near the window for a window AC. So, I would like to put the 6-15R there since there is already a hole to run the wire up from the basement once I remove the existing wire. If I need to cut the existing hole in the baseboard larger to accommodate a larger box, not a problem.

Regarding: The breaker or fuses needs to match the size required by the A/C unit (probably 15A or 20A)

This is the big question for me. It calls for 15A. So, all I need to do at the box is swap the 30A fuses with 15A and I will be OK? Out of curiosity, what is the risk? My understanding was that as long as the wire and fuse are greater than or equal to the appliance youíre OK. I am willing to swap fuses at the box, but beyond that I will hire somebody. Thanks again!
 
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Old 07-23-15, 10:18 AM
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[10-3 Romex type in good condition] from the range to the AC location... So, all I need to do at the box is swap the 30A fuses with 15A and I will be OK?
You don't need 10-3 but if this is old wiring the real problem is it may not have a ground. As Ben wrote no ground it can't be used. You can not re-purpose one of the wires as ground because code says wires that small must be factory marked.

A NEMA 6-20r also accepts a 6-15p so I would run 12-2 and use the 6-20r with 15 amp fuses. If you ever get an A/C that needs a 20 amp circuit you will only need to change the fuses.
 

Last edited by pcboss; 07-23-15 at 05:08 PM.
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Old 07-23-15, 10:33 AM
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The current 20A receptacle was installed for and has been used for a small window AC. Iím looking to upgrade with a free much larger AC from my deceased parents house.

Iím not going to mess with changing the wires at the box myself. The information on the existing 220V wire in question is legible. What markings do I look for to determine if it has a ground wire? The previous work was done by a Pro, but now long retired, so Iím sure that if there was a ground wire he used it.

Thank you!
 
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Old 07-23-15, 10:56 AM
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A ground wire, if any, entering the box under the windowsill would be bare or green.

Tiny lettering printed on the wires themselves may include "250v" or "600v" or something like that. Something like "125v" would mean the wires cannot handle the 240 volts you want to convert the circuit to.
 
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Old 07-23-15, 11:50 AM
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I guess I'll have to kill the power and take a look at what wires are in the receptacle at the electric range end. A reference on this site indicates that if there is a ground wire it should have a G after the 10-3. For example, 10-3/G. I don't remember it saying that.

Or, I can just leave the AC at my deceased parents house for the buyer. The closing is next week and I don't want to take the AC if it's going to just sit around unused.

Thank you all for your direction. I guess this isn't as simple as I had hoped!
 
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Old 07-23-15, 12:32 PM
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Yes, the cable will have a G in the designation if it is type NM and if there is a ground wire. All type NM (Romex) since about the mid 80s should have a ground, and most NM since the 60s will have a ground. However sometimes electric stoves were installed with the slightly cheaper SER cable -- it looks a lot like NM but probably will not have a ground.

You can re-use the existing box as long as the existing wiring is also terminated in a covered box. Pull the old 120V circuit back down into the basement rafters and nail up a junction box there. Pull the cable into that box, wirenut off the wires and close the box with a blank plastic cover. I usually Sharpie the circuit number on it for future reference.
 
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Old 07-23-15, 12:40 PM
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Thanks IBPOOKS! I'll take a close look at that wire this weekend and go from there.
 
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