240V outlet to 120V using existing neutral

Reply

  #1  
Old 04-15-11, 11:52 AM
Member
Thread Starter
Join Date: Apr 2011
Location: USA
Posts: 3
240V outlet to 120V using existing neutral

Hello, I have a 1979-1980 condo which the bank conveniently painted over every single outlet making me go through and swap everyone out (damn low bid painters). Did all that but noticed the 240v outlet for the thru the wall ac has some conveniently located lines for all the daisy chained outlets in the room.

Specifically, there are 2-yellow lines going to the 240v outlet. And through the box are cut and pigtailed black and white lines for all the 120v outlets daisy chained together through the room. In the breaker the 240v is on a dual pole 15 amp circuit and the daisy chained outlets are on a single 15 amp circuit.

What I propose is to use one of the yellow hots from the 240v outlet with the neutral from the daisy chained to make a 120v multi wire branch circuit MWBC.

I kept going back and forth on it till I did additional research. At first I thought it would be fine, then I though it could overload the neutral with too much amperage, then researched it and found it cancels out the amperage so should be fine, then found it could be either depending on the polarity of the hots used.

As the 240v outlet uses a dual pole breaker I already know one of the wires is good and one is wrong for correctly wiring it. The question is how to determine which yellow wire is the correct yellow wire.

Now I have a multimeter and from playing with it this is what I understand. hot(+ or -) w/ neutral = 120v, hot (+) w/ hot (-) = 240 v, hot (+) w/ hot (+) = 0 v. Therefore when comparing the voltages across the yellow wires with the daisy chained black, I want the one which goes to 240V. That would be the yellow hot with the correct polarity to use in the MWBC such that the amperage is canceling instead of adding over the neutral line?

(I could always get a 230v air conditioner but they tend to be more expensive then their 115v counterparts. I still might in the end, I just want to know if this is a viable methodology to providing a dedicate 15amp 120v outlet for the AC separate from the other outlets. I am an engineer, just not in electricity =p )
 
Sponsored Links
  #2  
Old 04-15-11, 12:22 PM
Forum Topic Moderator
Join Date: Feb 2005
Location: Near Lansing, Michigan
Posts: 10,288
Are the yellow wires for the 240V circuit in conduit? You could pull a neutral to make the 240V circuit a proper 120/240V multiwire.
 
  #3  
Old 04-15-11, 12:26 PM
chandler's Avatar
Banned. Rule And/Or Policy Violation
Join Date: Dec 2005
Location: USA
Posts: 39,968
Welcome to the forums! With Alternating Current there are no + or -, so we'll skip that. Most likely what you have is two yellow wires which carry 120 volts each from the panel, making a total of 240 volts when measured across the two yellow wires. Do you also have a white neutral wire??
Basically with changes in the panel box and in that receptacle box, you can attain what you want to do. Now the real question. Why? Aren't there enough receptacles close enough to this one to accommodate what you need? The 240 volt air conditioners are much more cost efficient than the 120 volt ones, and some will offer a heat mode, similar to a heat pump.
Methodology is there, but you will have to disable the double breaker supplying that receptacle, cap off one of the yellow wires, buy a new single breaker depending on the size of wire you have, cap off the same yellow wire in the receptacle box, marking it for the future owner, and use only the yellow wire and the neutral you have.
Others may have different ideas, but I say leave well enough alone, use the receptacles you have and plan for the future.
 
  #4  
Old 04-15-11, 12:50 PM
ray2047's Avatar
Group Moderator
Join Date: Mar 2006
Location: USA
Posts: 32,636
what you have is two yellow wires which carry 120 volts each from the panel, making a total of 240 volts
I know you know that isn't true. Each wire is one side of the 240v feed to your house. 120v comes one of those and the neutral.
 
  #5  
Old 04-15-11, 01:06 PM
pcboss's Avatar
Forum Topic Moderator
Join Date: Jul 2002
Location: Maryland
Posts: 14,354
It sounds like you have a conduit system. This would make it fairly easy just to pull in new conductors and leave the existing 240 volt alone for future use.
 
  #6  
Old 04-15-11, 01:50 PM
chandler's Avatar
Banned. Rule And/Or Policy Violation
Join Date: Dec 2005
Location: USA
Posts: 39,968
"I know you know that isn't true." Maybe I missed something. Sorry if I did.
 
  #7  
Old 04-15-11, 03:06 PM
Member
Thread Starter
Join Date: Apr 2011
Location: USA
Posts: 3
Originally Posted by chandler View Post
With Alternating Current there are no + or -, so we'll skip that. Most likely what you have is two yellow wires which carry 120 volts each from the panel, making a total of 240 volts when measured across the two yellow wires. Do you also have a white neutral wire?? Basically with changes in the panel box and in that receptacle box, you can attain what you want to do. Now the real question. Why? Aren't there enough receptacles close enough to this one to accommodate what you need? The 240 volt air conditioners are much more cost efficient than the 120 volt ones, and some will offer a heat mode, similar to a heat pump.
Methodology is there, but you will have to disable the double breaker supplying that receptacle, cap off one of the yellow wires, buy a new single breaker depending on the size of wire you have, cap off the same yellow wire in the receptacle box, marking it for the future owner, and use only the yellow wire and the neutral you have.
Others may have different ideas, but I say leave well enough alone, use the receptacles you have and plan for the future.
I only mentioned + and - in reference to the opposing poles of the two hot lines, easier then me drawning the sine waves out for inversing waves _/-\_ vs -\_/- =p However the inversed waves are fundamentally important for this to work.

As I said there is a neutral wire but its for a seperate circuit which comes off the daisy chained outlets. That was the task at determining which hot has the correct polarity to go with the the other circuits neutral.

240v AC's tend to be more expensive. As for efficiency from what I see the 120v AC's tend to have higher EER. Also they have a larger range of units, 240v outlets typically come in 10,000btu+ configurations, while 120V start at 5000btu and up. My room doesn't need that large of one. But I still want the AC on its own breaker separate from my other equipment.

Why would I need to change the dual pole breaker to a single one? It still provides 15amp over a single line, the 2nd hot would just be capped off and unused essentially turning the dual breaker into a single breaker in purpose. Just because its unused means it needs to be removed and changed?

@iBrooks Pulling a new line in to add a netural is about the most time consuming and largest amount of effort out of possible solutions, so would prefer not to. Especially if all it takes is taking a couple minutes to swap wires that are already in the outlet. (conduit is also pretty full with all the other daisy chained lines and this condo also has no attic or crawlspace so running new lines would really be a b....)
 
  #8  
Old 04-15-11, 03:33 PM
Member
Join Date: Mar 2006
Location: Wet side of Washington state.
Posts: 18,356
What I would do is to disconnect one of the yellow wires from the two-pole circuit breaker and then connect it to the ground bus. Disconnect both yellow wires from the 240 volt receptacle and then use an ohmmeter or continuity tester to determine which wire was connected to ground. Wrap a piece of white tape on this wire and remove the wire from the ground bus and also wrap some white tape on it. Then connect it to the neutral bus.

Then reconnect both wires onto a 120 volt receptacle being sure to put the wire with the white tape on the silver-colored terminal. Now you have a dedicated 120 volt receptacle.

While it is not technically allowable to "re-identify" conductors smaller than #4 I wouldn't let that stop me from doing so. It is also not a good practice to use only one pole of a two-pole circuit breaker but that is also a minor infraction in my mind. You could replace the two-pole circuit breaker with a single-pole and a blanking plate if you so desired.
 
  #9  
Old 04-15-11, 04:17 PM
chandler's Avatar
Banned. Rule And/Or Policy Violation
Join Date: Dec 2005
Location: USA
Posts: 39,968
If you are leaving this receptacle dedicated to the future air conditioner and want a 120 volt unit, then as Furd says, you can reidentify one of the yellows as as a neutral, while not technically correct to do so. + and - would only last a fraction of a second before they changed, so we just indicate whether they wire is energized or neutral or ground. For $5 I would change the breaker not only to leave space for another circuit, but to alleviate confusion. Sure you can do it with one leg of a 240v breaker.
Seems you had your mind set before asking questions and get upset at the answers you are given. You obviously have a knack for electrical work. So with the suggestions given, good luck with the project.
 
  #10  
Old 04-15-11, 08:08 PM
Member
Thread Starter
Join Date: Apr 2011
Location: USA
Posts: 3
Thanks for your input, not so much of upset as me not defining the question well. Perhaps I gave too much information and should have left the question posed as, how to verify a MWBC is wired correctly using a multimeter. Type of ac to use or running wire across the entire unit were a little beyond scope.

I thought the same as Furd's for the most common sense solution. I was just trying to avoid opening up the breaker panel if possible. And use the solution with the least amount of work.

Didn't know about the re-labeling a wire as against code for under a #4 tho but I also don't think its too large of an issue as long as everything is technically sound.

Other option I thought of is to cut the daisy chained black hot closest to the breaker at the last outlet. Then use one yellow hot to the black pigtail at the existing 240v outlet, and the other hot yellow to the new 120v dedicated AC outlet. Essentially the breaker on the existing daisy chained is no longer connected and the dual breaker is powering both the daisy chain and the AC. I would know for a fact both hots are on opposite polls. Also a little more legal as to my understanding MWBC's need to be on dual breakers so if one circuit trips the whole MWBC trips, but that might be another one which is minor.
 
  #11  
Old 04-18-11, 08:37 AM
Forum Topic Moderator
Join Date: Feb 2005
Location: Near Lansing, Michigan
Posts: 10,288
Originally Posted by enlight10ment View Post
how to verify a MWBC is wired correctly using a multimeter.
To verify the voltage is correct, the two hot legs should measure 240VAC between them and each hot should measure 120VAC to neutral.

I thought the same as Furd's for the most common sense solution.
Yes it is the most straightforward, but as Furd mentioned not a completely compliant option. If you take it I would recommend a little note on the wire "converted 240V air conditioner to 120V" to indicate what happened. That type of information helps tremendously in future troubleshooting.

Other option...Also a little more legal as to my understanding MWBC's need to be on dual breakers so if one circuit trips the whole MWBC trips, but that might be another one which is minor.
The problem with this proposed option is that MWBCs also require mechanical fasteners independent of the device on the shared neutral conductors, so you would have to visit each receptacle and switch on the circuit to verify that the neutral was spliced with wirenuts instead of using the device screws. This is to ensure integrity of the neutral conductor in the event of a broken receptacle. The double-pole breaker for MWBC is also required.

Of the given options, I think your best course is to re-identify one of the yellows as a neutral and move it to the neutral bus in the panel. This option also allows you or a future owner to easily convert back to a 240V air conditioner if necessary.
 
  #12  
Old 04-18-11, 07:05 PM
Justin Smith's Avatar
Member
Join Date: Dec 2010
Location: Cressona, Pa, USA
Posts: 2,546
What room is this in? Afci may also be req'd.
 
Reply

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread
Display Modes
'