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#97009 - 01/17/06 08:43 PM sharing neutral  
sparkync  Offline
Member
Joined: Oct 2002
Posts: 828
NC
Is there any conditions for 120 volt circuits where you can't share the neutral?
I am wiring circuits for computers in a customer's new business location. I have a 3 phase service and am planning on pulling 3 phase conductors and 1 neutral. Wondering if I am missing something on these computer circuits. Also have some copiers that I am planning on doing the same with. Any comments yea or nay will be appreciated. I believe I'm right according to code, but just double checking. Thanks, Steve


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#97010 - 01/17/06 08:51 PM Re: sharing neutral  
Dnkldorf  Offline
Member
Joined: Dec 2004
Posts: 1,064
nowhere usa
I'll tell you don't do it.

I Don't share nuetrals in a commercial enviroment for many reasons, from harmonics, to burning the place down due to a loose nuetral on one of the multiwire circuits you ran..


Dnk...


#97011 - 01/17/06 09:02 PM Re: sharing neutral  
Roger  Offline
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Joined: May 2002
Posts: 1,716
N.C.
Steve, for electronic circuits it is a good idea to use an oversized neutral (super neutral) for three phase multi-wire branch circuits or use two wire circuits.

Other than that, multi-wire branch circuits are some of the most sensible wiring methods used.

Roger


#97012 - 01/17/06 09:24 PM Re: sharing neutral  
renosteinke  Offline
Cat Servant
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Joined: Jan 2005
Posts: 5,316
Blue Collar Country
A lot of attention has been given to "isolated grounds" for computers and the like. This also a real market sor surge suppression and UPS (back-up power) systems.

While not required by code, nor ever mentioned in the specs for any such system, it is my practice to NOT share the neutral between separate circuits.
By running a dedicated nuetral, I avoid the whole harmonics issue. More important, to me, is that I also eliminate one source of a voltage surge- a loose neutral connection. I'll even go so far as to identify the neutrals in the panel and junction boxes.

You are correct in your understanding of the code- this is just one area where I chose to go "beyond" code minimums.


#97013 - 01/17/06 09:41 PM Re: sharing neutral  
Dnkldorf  Offline
Member
Joined: Dec 2004
Posts: 1,064
nowhere usa
Typically, for commercial applications, I will also run oversized wiring too.

By doing that, you avoid the multiwire disasters, and you also reduce line losses, where some believe, this is an advantage of a multiwire cicuit.


Dnk...


#97014 - 01/17/06 09:45 PM Re: sharing neutral  
iwire  Offline
Moderator
Joined: Jan 2003
Posts: 4,391
North Attleboro, MA USA
Gee I have no disasters and I run a lot of multiwire branch circuits.

Quote
By running a dedicated nuetral, I avoid the whole harmonics issue.


What do you do at the panel?

[This message has been edited by iwire (edited 01-17-2006).]


Bob Badger
Construction & Maintenance Electrician
Massachusetts

#97015 - 01/17/06 09:54 PM Re: sharing neutral  
Dnkldorf  Offline
Member
Joined: Dec 2004
Posts: 1,064
nowhere usa
Bob, went on one last week, someone ran a 3 circuit, one nuetral to multiple outlets, simlilar to what the poster is asking.
Aparently, a nuetral connection came loose in a recptacle box. All the surge protectors plugged in smoked and melted, the printer/copier burnt up, and needed boards, fire dept called, the whole mess.

For the cost of wire, and the potential for disaster, I don't do it.

Just for fairness, multiwires are good for lighting, if both circuits are matched closely.


Dnk...


#97016 - 01/17/06 10:05 PM Re: sharing neutral  
Roger  Offline
Member
Joined: May 2002
Posts: 1,716
N.C.
Dnk, it's not just the cost of wire, it's also natural resources including fuel for generation.

We literally install thousands of multi-wire circuits every year and I only know of one open neutral problem we have had in the last ten years, which had been tampered with by the particular facilities maintenance staff.

John, a dedicated grounded conductor to one ungrounded conductor is not a neutral. [Linked Image]

I have seen more open service neutrals than branch circuit or feeder neutrals by far.

Roger

[This message has been edited by Roger (edited 01-17-2006).]


#97017 - 01/17/06 10:06 PM Re: sharing neutral  
iwire  Offline
Moderator
Joined: Jan 2003
Posts: 4,391
North Attleboro, MA USA
I will install what the specifications allow or require.

My preference on longer circuits is multiwire. [Linked Image]


Bob Badger
Construction & Maintenance Electrician
Massachusetts

#97018 - 01/17/06 11:20 PM Re: sharing neutral  
gfretwell  Offline


Member
Joined: Jul 2004
Posts: 9,123
Estero,Fl,usa
Reno is right about IG.
I was an installating planning rep at IBM for 5 of my years there. Isolated Ground is a waste of money. IBM stopped mentioning it in the Carter administration but the legend lives on in the mind of "experts". If you like the customer, save them some money and talk them out of it. If they really insist, money is not an issue for them so sell them "monster" super neutrals at the appropriate price. Then you can take the family to Hawaii this summer.


Greg Fretwell

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