# 120/208V Three Phase Neutral Sharing



## Big John (May 23, 2010)

Sounds like the old scare of either "It's gonna open and burn everything!" or "Harmonics everywhere are causing overloads!" 

Those are hogwash 99% of the time. MWBCs are fine, especially for your small appliance loads.


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## sparky80 (Aug 1, 2016)

That is what I was thinking. Using the proper three phase breaker I see no issue, but wanted to make sure I'm not "out of the loop" with my thinking. Thanks again.


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## Signal1 (Feb 10, 2016)

Agree with John. Where did you read this article?


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## HackWork (Oct 2, 2009)

sparky80 said:


> That is what I was thinking. Using the proper three phase breaker I see no issue, but wanted to make sure I'm not "out of the loop" with my thinking. Thanks again.


 Using a 3-pole breaker is new and it was only put into the code to keep people who don't know what they are doing safe. There is no other issue, the breaker doesn't even have to be common trip, so you can use a handle tie.



Signal1 said:


> Agree with John. Where did you read this article?


+1

I was wonder where the article came from and what reasons they gave.


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## frenchelectrican (Mar 15, 2007)

sparky80 said:


> I recently read an article that stated the method of sharing the neutral from three phase 120 volt is no longer a good practice. I have a job that I would like to add two hots to a pipe and share the neutral on a three pole breaker. The loads involved are for a break area so items like microwaves, toaster ovens, etc. Thanks in advance.


Where did you find that article ??

basically as Hackwork saying I am in same situation as he is.

I am aware of one part about multiwire branch circuit they will required handle tie or common tripping on multipole breakers. 

The cost of three pole breaker vs three single pole breakers with handle tie is pretty wide margin depending on what brand breaker ya facing.,,

I been running full boat system pretty often and I dont useally see much issue beside some unqualifed dolts try to work on multiwire system which it get them hard.


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## sparky80 (Aug 1, 2016)

Found the article in a google search while looking for a 3 phase neutral load calculator. It was mostly mentioning noise and excessive loading from fluorescent and computer loads. I will see if I can find it again.


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## Bird dog (Oct 27, 2015)

sparky80 said:


> Found the article in a google search while looking for a 3 phase neutral load calculator. It was mostly mentioning noise and excessive loading from fluorescent and computer loads. I will see if I can find it again.


Third order harmonics (180hz) from nonlinear loads are a different issue. It depends on the load. "Generally speaking" you can balance A, B & C phase on a neutral.


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## RePhase277 (Feb 5, 2008)

Bird dog said:


> Third order harmonics (180hz) from nonlinear loads are a completely different issue.


And as an issue themselves, also completely overblown.


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## Big John (May 23, 2010)

I'm not even sure harmonics are a huge deal anymore. Seems like the folks who know that would be an issue are building in mitigation: 

Just looked at a site where they had about 4,000A of LED and discharge lighting, all electronic ballasts, and THD was still <5%.


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## Byte (Oct 3, 2016)

sparky80 said:


> Found the article in a google search while looking for a 3 phase neutral load calculator. It was mostly mentioning noise and excessive loading from fluorescent and computer loads. I will see if I can find it again.


Use a clamp-on?


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## Spark Master (Jul 3, 2012)

There are 10 zillion of these installations, with single pole breakers.


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## Switched (Dec 23, 2012)

Big John said:


> Sounds like the old scare of either "It's gonna open and burn everything!" or "Harmonics everywhere are causing overloads!"
> 
> Those are hogwash 99% of the time. MWBCs are fine, especially for your small appliance loads.


One day in the future they will theorize about the lost cities.... the ones that burnt to the ground over MWBC's, lack of AFCI protection, and NM cable installed in a basement.......

But... I just saved 10% on my auto insurance, so I am good!


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## active1 (Dec 29, 2009)

Must have been reading some Fkn liberal hating Edison circuit propaganda.

You are correct.
Our legal right to share whitty has been under attack.
Handel ties, not on these circuits, no more standard SP breakers.
Got those dang alternative lifestyle SP ark fault breakers.
Put everything else on GFIs with child proof receptacles.

96 NEC was more than plenty safe.
Bring back the super neutrals.

The way things are they may ban anything with exposed terminals when opened.
Can't use those receptacles no more cause they don't have screw covers.

And ballets disconests. Don't get me started.


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## Frasier (Jun 9, 2017)

sparky80 said:


> I recently read an article that stated the method of sharing the neutral from three phase 120 volt is no longer a good practice. I have a job that I would like to add two hots to a pipe and share the neutral on a three pole breaker. The loads involved are for a break area so items like microwaves, toaster ovens, etc. Thanks in advance.


The only significant potential problem I see is when you have one of the phases feeding another space and you drop the shared neutral. But a good electrician is supposed to know what all of the wires are feeding before he disconnects them.


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## Spark Master (Jul 3, 2012)

I used to call it an apprentice killer.


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## jjosuejimrod (Jun 14, 2017)

The use of different forms of wiring depends on the original design of the building. If the building was designed for use of incandescent lamps you can not replace those lamps with LED or electronic ballasts. Because you run the risk of polluting your neutral with harmonics.


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## frenchelectrican (Mar 15, 2007)

jjosuejimrod said:


> The use of different forms of wiring depends on the original design of the building. If the building was designed for use of incandescent lamps you can not replace those lamps with LED or electronic ballasts. Because you run the risk of polluting your neutral with harmonics.


Do you have anything to proof this claim ??


All the conversion I done and with flourscent or LED the THD I ran into are very low numbers and I am not really worry about it too much at all.

and I am not the only one I done this and many other done the same pattern as i did.,, 

just look up few posting above me and one guy say one large place have over 4K amps of ballasted load plus LED and the THD is less than 5% so that is a good number.


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## Spark Master (Jul 3, 2012)

jjosuejimrod said:


> The use of different forms of wiring depends on the original design of the building. If the building was designed for use of incandescent lamps you can not replace those lamps with LED or electronic ballasts. Because you run the risk of polluting your neutral with harmonics.


Only in theory......

10 zillion buildings converted to LED, no problems. 
The current draw is so low, harmonics would be insignificant.


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## brian john (Mar 11, 2007)

jjosuejimrod said:


> The use of different forms of wiring depends on the original design of the building. If the building was designed for use of incandescent lamps you can not replace those lamps with LED or electronic ballasts. Because you run the risk of polluting your neutral with harmonics.


I have literally completed 100's if not 1000's of load studies utilizing Line Disturbance analyzers and not one showed a high level of voltage harmonics. 

I hear this all the time and while I'll gladly complete a study for the customer I have yet to see an issue from lighting.


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## active1 (Dec 29, 2009)

jjosuejimrod said:


> The use of different forms of wiring depends on the original design of the building. If the building was designed for use of incandescent lamps you can not replace those lamps with LED or electronic ballasts. Because you run the risk of polluting your neutral with harmonics.


Incandescent to LED conversion reduces the load 80-90%.
Your plenty fine with that.
To go the other way around wouldn't work but who would go that direction.

Building design???
That's a hoot.


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## brian john (Mar 11, 2007)

sparky80 said:


> I recently read an article that stated the method of sharing the neutral from three phase 120 volt is no longer a good practice. I have a job that I would like to add two hots to a pipe and share the neutral on a three pole breaker. The loads involved are for a break area so items like microwaves, toaster ovens, etc. Thanks in advance.


Where did you read this article and who was the author? Typically the authors of such articles work for firms that manufacture Harmonic mitigation devices.


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## ggratecc (Mar 25, 2008)

About 8 months ago I was called to trouble shoot site lighting and Commercial sign outage. An open neutral was found in a buried JB for this 3 phase 120/208 circuit.

I found that the circuit was supplied by 3 single CB's no handle ties. Of course, I found 208v on one leg and about 50v on another leg, causing the commercial sign ballast damage and all LED site lighting bulbs to blow. 

In this case I just repaired/replaced bad neutral wiring (waterproof wire nuts), made JB cover raised above ground, with bolt on the cover and engraved "electrical" on cover, replace cb's with a 3-pole cb single handle.

Also, created a documentation file (with photos) on this circuit to make it easier for the facility manager.
Bottom line, I would never propose a new 3-phase MWBC circuit with single phase loads like this, although it is allowed.


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## Byte (Oct 3, 2016)

*Kudos*



ggratecc said:


> About 8 months ago I was called to trouble shoot site lighting and Commercial sign outage. An open neutral was found in a buried JB for this 3 phase 120/208 circuit.
> 
> I found that the circuit was supplied by 3 single CB's no handle ties. Of course, I found 208v on one leg and about 50v on another leg, causing the commercial sign ballast damage and all LED site lighting bulbs to blow.
> 
> ...


Good job. Yes, unfortunately, a 3 phase beaker does not isolate only 3 phase loads


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## B-Nabs (Jun 4, 2014)

Sometimes things break. That is not a reason to eschew a completely functional and economical wiring method. I love sharing neutrals. I also love that in Canada we don't have to deal with that handle tie nonsense. 

Sent from my SM-G920W8 using Tapatalk


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## brian john (Mar 11, 2007)

B-Nabs said:


> Sometimes things break. That is not a reason to eschew a completely functional and economical wiring method. I love sharing neutrals. I also love that in Canada we don't have to deal with that handle tie nonsense.
> 
> Sent from my SM-G920W8 using Tapatalk


 . I agree

It is a simple wiring method that works and when installed by a professional is perfectly fine. If we can't handle MWBC then we need to outlaw Fused Safety Switches.


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## telsa (May 22, 2015)

jjosuejimrod said:


> The use of different forms of wiring depends on the original design of the building. If the building was designed for use of incandescent lamps you can not replace those lamps with LED or electronic ballasts. Because you run the risk of polluting your neutral with harmonics.


Haha. :thumbsup:

What a troll post.


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## telsa (May 22, 2015)

ggratecc said:


> About 8 months ago I was called to trouble shoot site lighting and Commercial sign outage. An open neutral was found in a buried JB for this 3 phase 120/208 circuit.
> 
> I found that the circuit was supplied by 3 single CB's no handle ties. Of course, I found 208v on one leg and about 50v on another leg, causing the commercial sign ballast damage and all LED site lighting bulbs to blow.
> 
> ...


I've installed more of them than I can count.

They happened because of late-in-the job extras....

Suddenly, they became naughty -- so as to increase the $$$ for the NEMA players.

BTW, a screwed up neutral is a screwed up neutral. 

Breaker games are not going to cure a screwed up neutral.


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## Byte (Oct 3, 2016)

brian john said:


> . I agree
> 
> It is a simple wiring method that works and when installed by a professional is perfectly fine. If we can't handle MWBC then we need to outlaw Fused Safety Switches.


All I maintain is that a neutral of a three phase system for lighting or receptacles is great; however, if for mechanical, heating, or other dedicated circuits that require no neutral, the CB should be tandem.


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## telsa (May 22, 2015)

L-L loads demand coupled breakers.

As do L-L-L loads. ( ie 3-phase motor loads, etc. )


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## active1 (Dec 29, 2009)

ggratecc said:


> I found that the circuit was supplied by 3 single CB's no handle ties
> [or] waterproof wire nuts
> made JB cover raised above ground,
> with bolt on the engraved "electrical" on cover
> ...


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## ggratecc (Mar 25, 2008)

active1;4607810
If it was possible a better fix would have been to re-pull the circuits so there is no splice underground or anywhere else between the sign and source (building?). Less splices = less problems.[/QUOTE said:


> I'm glad you reminded me about this idea. I could have re-pulled as you said to the very end of the line.


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## Going_Commando (Oct 1, 2011)

brian john said:


> I have literally completed 100's if not 1000's of load studies utilizing Line Disturbance analyzers and not one showed a high level of voltage harmonics.
> 
> I hear this all the time and while I'll gladly complete a study for the customer I have yet to see an issue from lighting.


God damnit. I am on a job now where I did all the lighting circuits with separate neutrals since that is what they taught me in trade school. I could have saved quite a bit of work if I could have shared neutrals. Bastards.


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## PokeySmokey (Nov 14, 2017)

Going_Commando said:


> God damnit. I am on a job now where I did all the lighting circuits with separate neutrals since that is what they taught me in trade school. I could have saved quite a bit of work if I could have shared neutrals. Bastards.


Whoever the instructor was did not have knowledge and experience with 3 phase lighting circuits. I started my apprenticeship in the early 1960's and we were thoroughly informed about multi-phase circuits and where you could and could not use common neutrals rather than separate commons.

You know now!


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