# Dumb shared neutral question



## five.five-six (Apr 9, 2013)

dspiffy said:


> But I am curious: other than it being against code, what is the argument against simply tying all three neutrals together in the junction box?


Electrolysis, 1 of the neutrals will have a lower resistance than the others, assuming that you are talking about an armored 12/3, eventually the current imbalance will burn through the armor.


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## dspiffy (Nov 25, 2013)

It's actually romex. Most of this building is wired in romex. I am converting it to EMT in most of the areas I've been working on.


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## five.five-six (Apr 9, 2013)

dspiffy said:


> It's actually romex. Most of this building is wired in romex. I am converting it to EMT in most of the areas I've been working on.


You still run the risk of overloading a nuter. I don't see a lot of romex in 3∅ locations


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## dspiffy (Nov 25, 2013)

This building went up around 1980, and was originally 3 floors of offices. 600 amp 3 phase service, 200 amp main panel and a 150 amp sub panel on each floor. EVERYTHING original to the building was romex, involving some of the thickest romex I've ever seen, and quite a few rats nests of wires. Over the years, as previous owners/tenants remodeled, there were a lot of changes made, and a lot of BX wire added. Also a lot of walls that were cut through, wire and all. Most of the work original to the building appears to have been done very well, but there were clearly some subsequent hack jobs. This shared neutral error is the first thing I've seen that's clearly original to the building and clearly . . . bad.

I'm trying to understand why anything would overload if they're all three tied together at both ends.


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## five.five-six (Apr 9, 2013)

Because it is impossible for all 3 nuters to have the exact same resistance. One of them will take more load than the others.


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## dspiffy (Nov 25, 2013)

How great a resistance difference would it need to be for one cable to carry more than 20 amps? Especially given that there are 3 opposing phases canceling each other?

I've seen this done on 2 phase before, I didnt touch it.


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## five.five-six (Apr 9, 2013)

Just don't be a hack, do it correctly. If the circuits are fully loaded, it won't take much imbalance to cause a heat issue.


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## dspiffy (Nov 25, 2013)

As stated earlier in the thread, I'm going to do it right, but I'd like to learn why.


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## Deep Cover (Dec 8, 2012)

Is there no one overseeing your work with the experience to answer that question?


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## BBQ (Nov 16, 2010)

Again I ask are you legally qualified to be doing this work?

Here is an example of what can happen.




http://www.christianitytoday.com/ct/2005/novemberweb-only/14.0.html


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## EBFD6 (Aug 17, 2008)

five.five-six said:


> Just don't be a hack, do it correctly. If the circuits are fully loaded, it won't take much imbalance to cause a heat issue.


I agree. Move the circuits around in the panel so the mwbc's are wired correctly.


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## hardworkingstiff (Jan 22, 2007)

dspiffy said:


> How great a resistance difference would it need to be for one cable to carry more than 20 amps? Especially given that there are 3 opposing phases canceling each other?
> 
> I've seen this done on 2 phase before, I didnt touch it.


I'm curious, what is it about your education level that allowed you to feel comfortable leaving code violating parallel neutral/sharing neutral circuits uncorrected?

Here is the thing, you really don't have the choice to decide which code you follow and which one you ignore without accepting the consequences of your decisions. You may never have a problem, but you don't know when you might. Karma can be a b1tch.


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## BBQ (Nov 16, 2010)

five.five-six said:


> Electrolysis,



:blink::001_huh::blink:


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## bkmichael65 (Mar 25, 2013)

BBQ said:


> :blink::001_huh::blink:


He may not be the most skilled electrician, but he has perfectly sculpted eyebrows


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## brian john (Mar 11, 2007)

five.five-six said:


> *Electrolysis*, 1 of the neutrals will have a lower resistance than the others, assuming that you are talking about an armored 12/3, eventually the current imbalance will burn through the armor.


 
Electrolysis-Explanation please.


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## five.five-six (Apr 9, 2013)

try it, running neutral in 1 conduit and your load in another conduit come back in 10 years and you will see accelerated corrosion


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## Ultrafault (Dec 16, 2012)

brian john said:


> Electrolysis-Explanation please.


I believe he meant to say subhodroxinatingelectoparanesis


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## HawkShock (Nov 27, 2012)

five.five-six said:


> try it, running neutral in 1 conduit and your load in another conduit come back in 10 years and you will see accelerated corrosion


So we have to go out of our way, do some hack work and then..... wait a decade for an answer?
uhmm, I'll just believe you.


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## BBQ (Nov 16, 2010)

five.five-six said:


> try it, running neutral in 1 conduit and your load in another conduit come back in 10 years and you will see accelerated corrosion


I find that unlikely.


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## gnuuser (Jan 13, 2013)

brian john said:


> Electrolysis-Explanation please.


heres a wiki on it
http://en.wikipedia.org/wiki/Electrolysis


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## hardworkingstiff (Jan 22, 2007)

gnuuser said:


> heres a wiki on it
> http://en.wikipedia.org/wiki/Electrolysis


From your link


> Electrolysis is the passage of a *direct electric current* through an ionic substance that is either molten or dissolved in a suitable solvent, resulting in chemical reactions at the electrodes and separation of materials.
> The main components required to achieve electrolysis are :
> An electrolyte : a substance containing free ions which are the carriers of electric current in the electrolyte. If the ions are not mobile, as in a solid salt then electrolysis cannot occur.
> A *direct current (DC) supply* : provides the energy necessary to create or discharge the ions in the electrolyte. Electric current is carried by electrons in the external circuit.
> Two electrodes : an electrical conductor which provides the physical interface between the electrical circuit providing the energy and the electrolyte


I've always been taught that AC does not cause electrolysis.


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## dspiffy (Nov 25, 2013)

hardworkingstiff said:


> I'm curious, what is it about your education level that allowed you to feel comfortable leaving code violating parallel neutral/sharing neutral circuits uncorrected?
> 
> Here is the thing, you really don't have the choice to decide which code you follow and which one you ignore without accepting the consequences of your decisions. You may never have a problem, but you don't know when you might. Karma can be a b1tch.


Are you referring to the circuits I just discovered, or the ones I had I had seen years ago? If the latter, it wasnt on a job of any kind. The former, as already addressed, I plan to repair.


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## dspiffy (Nov 25, 2013)

BBQ said:


> Again I ask are you legally qualified to be doing this work?
> 
> Here is an example of what can happen.
> 
> ...


Please explain to me how shared neutrals can result in an electrified baptismal pool.


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## dspiffy (Nov 25, 2013)

I'm looking forward to the answers to others' questions. I cannot see how, on paper, this would cause a real issue.


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## Chrisibew440 (Sep 13, 2013)

We run parallel neutrals or "super neutrals"in schools all the time. As long as they're the same length you should be good.


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## five.five-six (Apr 9, 2013)

Chrisibew440 said:


> We run parallel neutrals or "super neutrals"in schools all the time. As long as they're the same length you should be good.


Do you put more than one round robin per "super neutral"


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## Chrisibew440 (Sep 13, 2013)

five.five-six said:


> Do you put more than one round robin per "super neutral"


Well. Sub panels are fed this way only. We'll oversize a neutral on a lot of circuits but panels will have a parallel.


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## Chrisibew440 (Sep 13, 2013)

Actually I'm not quite sure why either, the only thing I can come up with is that it cleans up the electricity for computers and some sensitive equipment. I'd like more info, someone have a fact about this?


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## RIVETER (Sep 26, 2009)

dspiffy said:


> I have an area fed by 6 20 amp circuits, from a distant panel, all into the same junction box. It's 3 runs of 12/3.
> 
> I finally took a look at this today and discovered that each run of 12/3 has two circuits on the same phase. All three phases are represented, but with three different neutrals, and each neutral could theoretically see 40 amps.
> 
> ...


None


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## Shock-Therapy (Oct 4, 2013)

hardworkingstiff said:


> From your link
> 
> I've always been taught that AC does not cause electrolysis.


Thats correct.:thumbsup: Polarity changes back and forth fast enough to neutralize the process.


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## BBQ (Nov 16, 2010)

dspiffy said:


> Please explain to me how shared neutrals can result in an electrified baptismal pool.


The point was poor wiring can result in deaths. You don't sound like a guy with the experience that should be doing this work in a public building.


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## five.five-six (Apr 9, 2013)

BBQ said:


> I find that unlikely.


Think about how the windings in a transformer work, running cable inside a ferrous conduit does the same thing, albeit less efficiently and takes up a lot more space but the same principles apply.


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## dspiffy (Nov 25, 2013)

Is there an argument to be made that it would allow more harmonic distortion (from dimmers, ballasts, etc) back onto the grid?


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