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#179650 - 07/25/08 04:13 PM Double up on a phase  
wiking  Offline
Junior Member
Joined: Dec 2002
Posts: 32
Florida, USA
I found a run that feeds three circuits of recepticles while sharing a neutral. The problem is that when I looked, the blue circuit is actually landed on the black phase, unbalancing the neutral I would imagine. Evidently it's been operating that way for awhile without any problems that are known about. It might help that the neutral is #10 on 20amp circuits, but are there any bad effects that might be coming about because of this?


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#179654 - 07/25/08 05:36 PM Re: Double up on a phase [Re: wiking]  
SolarPowered  Offline
Member
Joined: Jul 2004
Posts: 625
Palo Alto, CA, USA
The configuration you describe can result in as much as 40 amps on the #10 neutral, which is only allowed to carry 30 amps. So, yes, the installation is unsafe, and in violation of code.


#179655 - 07/25/08 06:42 PM Re: Double up on a phase [Re: wiking]  
junkcollector  Offline
Member
Joined: Apr 2007
Posts: 36
Central MN
Originally Posted by wiking
The problem is that when I looked, the blue circuit is actually landed on the black phase...


So is it just doubled up on the same breaker (black and blue on the same breaker), or is the breakers on the same phase in the panel? If it is on the same breaker, then it is considered the same circuit and there isn't really a problem. I assume otherwise...
Originally Posted by wiking

Evidently it's been operating that way for awhile without any problems that are known about.


There probably wasn't enough load on the circuit to load the nuetral wire to the point of overheating.

let us know...

Last edited by junkcollector; 07/25/08 06:42 PM.

#179656 - 07/25/08 06:47 PM Re: Double up on a phase [Re: junkcollector]  
SolarPowered  Offline
Member
Joined: Jul 2004
Posts: 625
Palo Alto, CA, USA
A clarifying question: It appears that you're saying that two of the three circuits (black and blue) actually land on the black phase. Is that correct? (That is what my above answer is based on.)


#179671 - 07/26/08 08:12 AM Re: Double up on a phase [Re: SolarPowered]  
wiking  Offline
Junior Member
Joined: Dec 2002
Posts: 32
Florida, USA
To clarify, there are three circuits on three different breakers sharing one neutral. The black wire is on the black phase, red on red, but the blue wire is landed on a black phase breaker on the other side of the panel.
This also brings up another point that I see all the time. I was told when I first came up that on a three phase panel if you shared a neutral that it better go with it's specific group. For instance there is one neutral for circuits 1,3,5 if they went to the same place. I wasn't allowed to use the same neutral to share with, say, 1,3, and 11, which would give you a neutral that has a black, red and blue phase on it, even though the 11 is out of sequence.
Is this common or do you find it acceptable to share any circuit numbers as long as they don't double up the phase?


#179672 - 07/26/08 08:54 AM Re: Double up on a phase [Re: wiking]  
renosteinke  Offline
Cat Servant
Member
Joined: Jan 2005
Posts: 5,316
Blue Collar Country
Funny you should ask ....

Prior to the 2008 NEC, you could use any breaker combination- at least, strictly according to the rules. The 2008, however, wants them grouped together, on a three-pole breaker, and the four wires (including neutral) zip tied together in the panel.


#179690 - 07/27/08 08:04 AM Re: Double up on a phase [Re: renosteinke]  
electure  Offline


Member
Joined: Dec 2000
Posts: 4,262
Fullerton, CA USA
Quote
on a three-pole breaker,


See 210.4 Multiwire Branch Circuits

The requirement is for:
"(B) Disconnecting Means. Each multiwire branch circuit
shall be provided with a means that will simultaneously
disconnect all ungrounded conductors at the point where
the branch circuit originates."

That seems to allow the use of listed handle ties as well.

And (D) "Exception: The requirement for grouping shall not apply if the circuit enters from a cable or raceway unique to the circuit that makes the grouping obvious"


#179691 - 07/27/08 09:04 AM Re: Double up on a phase [Re: electure]  
leland  Offline
Member
Joined: Aug 2007
Posts: 853
Lowell area, Ma. USA
210.4 (B)--
This is a common misconception. I've had many discussions on it.
The KEY: Common "DISCONNECT"- not trip.
Once this is pointed out I get the ole'..."Ohhh-Ya".

As far as "D", I still group a single conduit, For "Justin".. Just in case some one adds ckts to it.
How many times have you seen a pipe added to a disco,because it's closer,then conductors added to the original pipe?

Last edited by leland; 07/27/08 09:06 AM.

#179692 - 07/27/08 01:02 PM Re: Double up on a phase [Re: electure]  
renosteinke  Offline
Cat Servant
Member
Joined: Jan 2005
Posts: 5,316
Blue Collar Country
I can't argue with that, Scott. Perhaps it's my own bad grammar, but I have never made a distinction between a three pole breaker that had an internal trip mechanism, and one that had three handles tied together.

I agree that either would meet this particular code requirement.

I'm sure that everyone had already been grouping such conductors together, wherever possible. The 'common disconnect' is a new requirement, but not that big of a deal. Where practice gets changed is the requirement to literally tie the hots, as well as the neutral, together in their own bundle.
That's bound to be fun, especially in panels with only one neutral buss.


#179700 - 07/27/08 08:12 PM Re: Double up on a phase [Re: renosteinke]  
electure  Offline


Member
Joined: Dec 2000
Posts: 4,262
Fullerton, CA USA
John,
The price of a 3 Pole breaker with a common trip is substantially higher than 3 single pole units and a handle tie.


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