Multiwire circuit question

Reply

  #1  
Old 03-01-07, 09:31 PM
Member
Thread Starter
Join Date: Jun 2005
Location: USA
Posts: 106
Multiwire circuit question

In the process of some wiring cleanup, I noticed that someone had ran a multiwire circuit in our home. It appears to be ran correctly (on different legs in the panel).

I needed to re-do some circuits so I thought I would do the same thing (to save some wire/time/etc.) However, after reading some other posts on the web, I'm now concerned about what happens if one of the neturals comes loose. From what I read, it sounds like the entire circuit can go to 240V ?

I guess I'm confused - I ran 12/3 from the panel into a new JB and pulled all the branch feeds into that box. At the panel it is connected to 2 breakers on different legs (the breakers aren't tied yet, but they will be shortly). In the JB I connected all neturals together and split the 2 hots between the branch feeds (about 3 for each hot). Everything seems to be working correctly.

Also, I read something about not being able to use the passthrough on an outlet for the neutrals (they have to be pigtailed?) Not sure how that would affect my situation.

Thanks.
 
Sponsored Links
  #2  
Old 03-01-07, 09:49 PM
Member
Thread Starter
Join Date: Jun 2005
Location: USA
Posts: 106
Originally Posted by swallman View Post
In the process of some wiring cleanup, I noticed that someone had ran a multiwire circuit in our home. It appears to be ran correctly (on different legs in the panel).

I needed to re-do some circuits so I thought I would do the same thing (to save some wire/time/etc.) However, after reading some other posts on the web, I'm now concerned about what happens if one of the neturals comes loose. From what I read, it sounds like the entire circuit can go to 240V ?

I guess I'm confused - I ran 12/3 from the panel into a new JB and pulled all the branch feeds into that box. At the panel it is connected to 2 breakers on different legs (the breakers aren't tied yet, but they will be shortly). In the JB I connected all neturals together and split the 2 hots between the branch feeds (about 3 for each hot). Everything seems to be working correctly.

Also, I read something about not being able to use the passthrough on an outlet for the neutrals (they have to be pigtailed?) Not sure how that would affect my situation.

Thanks.
OK - I answered part of my question about pigtailing by searching for prior posts. From what I understand I shouldn't have to pigtail since I am splitting into the 2 circuits at the JB. From the JB on there should be no reason to pigtail.

Still a bit concerned about the possiblity of the 240V problem however.
 
  #3  
Old 03-01-07, 10:40 PM
Member
Join Date: Aug 2005
Location: San Francisco, CA
Posts: 749
aside from the 'about 3' branches you are attaching to the home run (just make sure you are not overloading the circuit), you do need to pigtail every neutral at every receptacle on any multiwire circuit.

The neutral, all the way from the panel to the last receptacle on the branch, is shared. Not just where you split off the 12/3.

It's not hard to do, and if it comes loose it won't cause a problem; not as much of a problem as if it wasn't pigtailed.
 
  #4  
Old 03-02-07, 05:31 AM
Member
Join Date: Sep 2003
Location: Central New York State
Posts: 13,973
Once you split the circuit, you do not need to pigtail the neutrals. Pigtails only need to be used on the neutral where it is shared.
 
  #5  
Old 03-02-07, 09:40 AM
Member
Join Date: Aug 2005
Location: San Francisco, CA
Posts: 749
I must be interpreting this wrong then, and everything that has been stated on this site about multi-wire circuits.

300.13(B) Device Removal. In multiwire branch circuits, the grounded conductor [neutral] shall not depend on device connections such as lampholders, receptacles, and so forth, where the removal of such devices would interrupt the continuity.
 
  #6  
Old 03-02-07, 09:46 AM
Member
Join Date: Sep 2003
Location: Central New York State
Posts: 13,973
Once you split a multi-wire circuit into two circuits, each with it's own neutral and hot, it is no longer multi-wire. If the neutral wire should happen to open, there would be no danger of (up to) 240 volts on the circuit, it would be just the same as the neutral failing on a plain two wire circuit.

The code is trying to prevent the unsafe and potentially damaging situation where a device may get up to 240 volts across it. Once you separate the multi-wire circuit, the 240 volt situation is no longer possible.
 
  #7  
Old 03-02-07, 09:52 AM
Member
Join Date: Aug 2005
Location: San Francisco, CA
Posts: 749
Thanks for the clarification Bob. From a response you made to a similar question on another thread:

"For a multiwire circuit you are not allowed to feed the neutral through a device. Instead the neutral must be pigtailed. This is because the neutral is very important. If the neutral gets disconnected then you could (depending on the circumstances) end up with 240 volts on your 120 volt devices, which would generally cause them to fail and possibly burn up.".

Don't take this the wrong way, I appreciate all the great advice that you have given to both myself and others on the board, but maybe in the future a clarification could be made as to when the neutral doesn't need to be pigtailed.

I know it would have saved me a ton of time, as I went around and pigtailed every neutral..
 
  #8  
Old 03-02-07, 10:20 AM
Member
Join Date: Sep 2003
Location: Central New York State
Posts: 13,973
fuente,

Without knowing what thread that came from it's hard to comment. However, I can only guess that the thread dealt with a multi-wire circuit that continued as multi-wire the whole length, or the comment was made in general.
 
  #9  
Old 03-02-07, 10:29 AM
Member
Join Date: Sep 2000
Location: United States
Posts: 18,497
This gives me a chance to emphasize to everyone that all advice given in any thread applies only to the specific situation being discussed in that one thread. It is very risky to apply advice given to someone else to yourself, unless you have exactly--in every minute detail--the same situation. When in doubt, ask you own question.
 
  #10  
Old 03-02-07, 11:02 AM
Member
Join Date: Aug 2005
Location: San Francisco, CA
Posts: 749
Here is the thread:

http://forum.doityourself.com/showthread.php?t=279139&highlight=shared+neutral
 
  #11  
Old 03-02-07, 03:23 PM
Member
Join Date: Sep 2000
Location: United States
Posts: 18,497
That other thread is a theoretical discussion. It did not attempt to cover all situations. There are always exceptions.
 
  #12  
Old 03-02-07, 03:25 PM
Member
Join Date: Aug 2005
Location: San Francisco, CA
Posts: 749
Talking

ok, if you say so...
 
  #13  
Old 03-02-07, 03:32 PM
Member
Join Date: Sep 2000
Location: United States
Posts: 18,497
You must pigtail the neutrals on a multiwire circuit...except when you don't have to. You must use a double-pole breaker on a multiwire circuit...except when you don't have to.
 
  #14  
Old 03-02-07, 03:40 PM
Member
Join Date: Aug 2005
Location: San Francisco, CA
Posts: 749
ok John. It just seemed like I asked a specific question in that thread, and got a specific answer.
 
  #15  
Old 03-02-07, 03:41 PM
Member
Thread Starter
Join Date: Jun 2005
Location: USA
Posts: 106
Talking

John,

I don't know you, but maybe you should run for political office! That sounds like an appropriate answer.
 
  #16  
Old 03-02-07, 03:46 PM
Member
Join Date: Sep 2000
Location: United States
Posts: 18,497
As long as everything is clear now, we're good.
 
  #17  
Old 03-02-07, 04:41 PM
Member
Join Date: Sep 2003
Location: Central New York State
Posts: 13,973
Not to further muddy the waters (I've caused enough trouble already), SOME people would say that once you separate the hot wires and have separate neutrals, you no longer have a multi-wire circuit.
 
  #18  
Old 03-02-07, 05:48 PM
Banned. Rule And/Or Policy Violation
Join Date: Feb 2006
Location: North of Boston, MA.
Posts: 2,113
Originally Posted by fuente View Post
ok John. It just seemed like I asked a specific question in that thread, and got a specific answer.
You did get a great answer. (i whent back).

"John,

I don't know you, but maybe you should run for political office! That sounds like an appropriate answer."

PLEASE!!! Why wreck a good honest inteligent man? Appropriate and honest answers are different. (from MA., need I say more?)

Don't do it John!
 
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