Use A Shared Nuetral Or Not? That Is The Question. - Electrical - DIY Chatroom Home Improvement Forum

 DIY Chatroom Home Improvement Forum Use a shared nuetral or not? That is the question.
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05-22-2008, 03:59 PM   #1
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## Use a shared nuetral or not? That is the question.

I am pulling out #12 wire, two circuits with a shared neutral and replacing with #10 wire. What are the benefits of keeping a shared neutral verses running each circuit with its own neutral?

It seems to me that when you run a shared neutral, it limits you to the usage because you have to make sure the loads are always balanced on the two circuits, you have to make sure that the two circuits are on opposite legs of the panel and use a common trip.

Would it be less complicated to run each circuit with its own neutral so that you don't have to be concerned about the loads??

What is the main reason that two circuits are run with a shared neutral..is it to save on wire costs or utility costs??

Thanks. Cyndi

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05-22-2008, 04:21 PM   #2
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What you're talking about is called a multiwire branch circuit, and what you've said is dead-on. Having the hot wires on opposite phases is critical. Balancing loads isn't critical because a pair of properly phased multiwire branch circuits act as two separate circuits, although they share the neutral...As long as the loads are within the limits of the circuit I think you're find.

Electricians run multiwire branch circuits to save on wire (for 3 wire you're only paying for 1 extra wire over 2 wire) costs and time it takes to pull two runs instead of one. It simplifies things in a lot of cases...Some people make it complicated though, and for them two separate 2 wire circuits are often best! It will not affect utility costs in any way.

 05-22-2008, 06:20 PM #4 Licensed Electrical Cont.     Join Date: Feb 2004 Location: NY State Posts: 7,811 Rewards Points: 1,972 Use the MWBC. There is not that much to think about and they can and do lessen voltage drop. The ONLY thing to remember is to keep the breakers on different legs. If you use a 2-pole breaker (now required if you are under the 2008 NEC) this is a non-issue. Balancing the loads on the circuits is also a total non-issue. We use MWBC's for more than just cost savings. There are other more important reasons as well. __________________ Sometimes I feel like if I answer any more questions it is like someone trying to climb over a fence to jump off a bridge and me giving them a boost.
 05-22-2008, 06:39 PM #5 Member   Join Date: Apr 2008 Location: Washington Posts: 146 Rewards Points: 75 Thank you for the info Speedy Petey! Also, do both circuits need to be #10 wire or can I run #12 for the 170 foot run and #10 for the 370 foot run with the shared neutral??? The only reason I ask is because I have plenty of #12 wire and need to buy all of the #10 wire as needed. I just need to know how much to put on the shopping list !!!! In other words...can the #10 share the same neutral with the #12 wire or should I run all #10 for these two long runs?? Cyndi __________________ Student of the great electrical GURU.....Stubbie!
 05-22-2008, 06:53 PM #6 Licensed Electrical Cont.     Join Date: Feb 2004 Location: NY State Posts: 7,811 Rewards Points: 1,972 I would do #10 all the way. 170' is far enough to justify it. __________________ Sometimes I feel like if I answer any more questions it is like someone trying to climb over a fence to jump off a bridge and me giving them a boost.
 05-22-2008, 06:59 PM #7 Member   Join Date: Apr 2008 Location: Washington Posts: 146 Rewards Points: 75 Thanks again!!! Cyndi __________________ Student of the great electrical GURU.....Stubbie!
 05-23-2008, 09:46 AM #9 Licensed Electrician     Join Date: Feb 2008 Location: central wisconsin Posts: 989 Rewards Points: 514 I was wondering how this project was coming. Hello all. __________________ John
 05-23-2008, 11:18 AM #10 Member   Join Date: Apr 2008 Location: Washington Posts: 146 Rewards Points: 75 Good Morning Stubbie!!! I get it now. Thanks a million!!! The project is going slower than I had hoped but since the inspector was out, I have been pretty sick and am still recovering. It's all good though. I have also been delaying somewhat until you are not so busy because I am sure that I will need your input!! Hope that's o.k. I will have some help pulling the #2 wire this weekend and then the rest will fall into place....I hope!!! I am so glad to see you post again. I miss you when you are not there!!!!! Cyndi __________________ Student of the great electrical GURU.....Stubbie!
 05-23-2008, 11:32 AM #11 Member   Join Date: Apr 2008 Location: Washington Posts: 146 Rewards Points: 75 I read somewhere in this forum that some GFCI's don't work on MWBC's. I had planned on putting GFCI receptacles at each location on the MWBC's that run out to all of the pastures. Would it be better to install GFCI breakers in the panel for these circuits or should I proceed as planned?? __________________ Student of the great electrical GURU.....Stubbie!
 05-23-2008, 11:34 AM #12 UAW SKILLED TRADES     Join Date: Jan 2007 Location: Kansas Posts: 5,341 Rewards Points: 2,652 I am incredibly busy at the present time but I check in almost every day. Seems the forum runs without missing a beat whether I'm here or not.... I'm also glad someone misses me.........
05-23-2008, 11:39 AM   #13
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Quote:
 Originally Posted by Cyndi I read somewhere in this forum that some GFCI's don't work on MWBC's. I had planned on putting GFCI receptacles at each location on the MWBC's that run out to all of the pastures. Would it be better to install GFCI breakers in the panel for these circuits or should I proceed as planned??
No. Use the receptacles. When you wire the gfcis to the line side, then continue to the next gfci, you no longer have a mwbc.
This is done all the time.

You would really hate being 370 feet from the panel and have to walk back to reset the breaker.
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 05-23-2008, 11:49 AM #14 Member   Join Date: Apr 2008 Location: Washington Posts: 146 Rewards Points: 75 jbfan- Just for clarification.....are you saying that when I install GFCI's at each location on MWBC's I will no longer have MWBC's or if I put GFCI breakers for the MWBC's I will no longer have MWBC's? Also, like I said.......someone on this forum stated that Some GFCI's don't work on MWBC's. Is there a certain type that I should get in exchange for the standard ones that I already purchased?? __________________ Student of the great electrical GURU.....Stubbie!
05-23-2008, 11:57 AM   #15

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Hi Cyndi

Here are your options I really have no preference. I would gfci with a double pole breaker. Only disadvantage is if it nuisance trips it is a long way back to the panel to reset it. I usually wire in an indicator light somewhere so you can monitor the condition of the multiwire circuit at the house or barn. If the light is on gfci is not tripped.... if off gfci is tripped.
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