# multiwire Kitchen branch circuit and shared neutral



## Perfectionist (Mar 26, 2021)

A panel has 2 single pole 20amp breakers for the kitchen with a shared neutral. The house has been there for years so I'm assuming this was done awhile ago. I'm trying to understand how this is ok on the neutral as it makes me nervous due to reading about how multiwire branch circuits should be tied via a handle tie or 2 pole breaker, which they are not. 

Any wisdom on this would be appreciated. Thank you


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## HertzHound (Jan 22, 2019)

It’s fine the way it is. If the electrician spliced the neutral through, and doesn’t rely on the device for continuity, it’s all good. Any qualified mechanic should know to shut off all the breakers of a multiwire branch circuit before opening the neutral splice.

<Rant>
Handle ties put one more nail in the coffin of the conduit trade. Most job specs don’t allow handle ties or multi-pole breakers on branch circuits. This eliminates shared neutrals and increases conduit fill and wire size due to derating. Just yank homerun MC to compensate.


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## LGLS (Nov 10, 2007)

Perfectionist said:


> A panel has 2 single pole 20amp breakers for the kitchen with a shared neutral. The house has been there for years so I'm assuming this was done awhile ago. I'm trying to understand how this is ok on the neutral as it makes me nervous due to reading about how multiwire branch circuits should be tied via a handle tie or 2 pole breaker, which they are not.
> 
> Any wisdom on this would be appreciated. Thank you


There are millions of multiwire branch circuits sharing neutrals in use today, with each circuit on an Edison plug fuse or on breakers not handle tied together. It was until recently perfectly legal and safe.


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## 460 Delta (May 9, 2018)

LGLS said:


> There are millions of multiwire branch circuits sharing neutrals in use today, with each circuit on an Edison plug fuse or on breakers not handle tied together. It was until recently perfectly legal and safe.


Just remember, last year’s safe compliant install is this year’s ticking time bomb.


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## joe-nwt (Mar 28, 2019)

460 Delta said:


> Just remember, last year’s safe compliant install is this year’s ticking time bomb.


I nominate this for post of the month!

Can I use it or is it copyright?


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## just the cowboy (Sep 4, 2013)

Perfectionist said:


> A panel has 2 single pole 20amp breakers for the kitchen with a shared neutral. The house has been there for years so I'm assuming this was done awhile ago. I'm trying to understand how this is ok on the neutral as it makes me nervous due to reading about how multiwire branch circuits should be tied via a handle tie or 2 pole breaker, which they are not.
> 
> Any wisdom on this would be appreciated. Thank you


Theory wise it is the same as incoming power and neutral, current is vectorially added so it can't exceed the current on a single phase ( excluding harmonics).
Safety wise with all wire tight and not working on circuit it is safe.
The issue is feedback when working on it if you open one breaker or open the neutral.
Other issue is if you open neutral while both circuits are hot you will get unstable voltage from 0-240 volts depending on loads connected. This will let the smoke out of 120 volt devices.

Cowboy


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## LGLS (Nov 10, 2007)

460 Delta said:


> Just remember, last year’s safe compliant install is this year’s ticking time bomb.


Will be replacing a friend's panel in a week. Guess how many Arc-faults I'm installing in their 3 bedroom 1968 ranch?


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## 460 Delta (May 9, 2018)

LGLS said:


> Will be replacing a friend's panel in a week. Guess how many Arc-faults I'm installing in their 3 bedroom 1968 ranch?


All of them, as you bow in obeisance to your governmental overlords.


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## kb1jb1 (Nov 11, 2017)

As for the notorious multiwire branch circuits what would you do? I went on a service call for a window AC unit tripping out the circuit breaker. When I took off the cover I noticed several multiwire circuits on twin breakers. The same twin breaker had both the black and red wire. It has been like that for over 20 years and the home owner is elderly and did not understand the problem. The white wire on one of them was brown. The choices were 1. Leave it alone and just fix what I was called for. 2. Put both black and red wires under the same breaker. 3. Keep the black on one leg and move the red to the other. There is no way for me to know where the other ends of the circuits are and there is a concern of sending 240 some where. I haven't used multiwire circuits for over 20 years because of the confusion it might cause down the road.


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## 460 Delta (May 9, 2018)

joe-nwt said:


> I nominate this for post of the month!
> 
> Can I use it or is it copyright?


As a pirate molded in the form of the late PeterD/MTW I believe in open source materials. You are free to use it whenever you feel it’s appropriate.

Please remember PeterD with kind thoughts. We miss you User4818.


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## kb1jb1 (Nov 11, 2017)

LGLS said:


> Will be replacing a friend's panel in a week. Guess how many Arc-faults I'm installing in their 3 bedroom 1968 ranch?


0? Why are you installing AFCI on a panel change unless you are relocating the panel and extending the circuits?


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## LGLS (Nov 10, 2007)

460 Delta said:


> All of them, as you bow in obeisance to your governmental overlords.


Not if they're not reptilian.


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## LGLS (Nov 10, 2007)

kb1jb1 said:


> 0? Why are you installing AFCI on a panel change unless you are relocating the panel and extending the circuits?


Good point, damn and I thought I was a rebel...


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## kb1jb1 (Nov 11, 2017)

LGLS said:


> Good point, damn and I thought I was a rebel...


I got scared there for a bit. I thought I missed something. They keep on adding or changing the codes and sometimes I do not know which one we are on.


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## 460 Delta (May 9, 2018)

LGLS said:


> Not if they're not reptilian.


Your need a “refresher” at the socio-political awakening camp. You are slipping into conservatism.


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## LGLS (Nov 10, 2007)

kb1jb1 said:


> I got scared there for a bit. I thought I missed something. They keep on adding or changing the codes and sometimes I do not know which one we are on.


Well it sure as hell doesn't help that we're not all on the same page now does it? I mean, someone asks a code question in 2021 and is like "We're on the 2015 but our unique amendments are still 2009..." Not to mention that some here claim if they touch anything in an older house their inspectors make them update totally unrelated things, and for sure some here believe that a panel change requires the arc-fault updates which I kinda knew didn't but in some jurisdictions they make you do it anyway.


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## LGLS (Nov 10, 2007)

460 Delta said:


> Your need a “refresher” at the socio-political awakening camp. You are slipping into conservatism.


I need a shower now.


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## 460 Delta (May 9, 2018)

LGLS said:


> I need a shower now.


I see.


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## Dennis Alwon (May 9, 2009)

Perfectionist said:


> A panel has 2 single pole 20amp breakers for the kitchen with a shared neutral. The house has been there for years so I'm assuming this was done awhile ago. I'm trying to understand how this is ok on the neutral as it makes me nervous due to reading about how multiwire branch circuits should be tied via a handle tie or 2 pole breaker, which they are not.
> 
> Any wisdom on this would be appreciated. Thank you



If the conductors are on different phase- usually next to each other- then the neutral will never seen more than 20 amps. The formula is N = Line 1- Line 2

put 20 amps on both hot conductors and the neutral will read 0-- strange but true.

Put 20 amps on 1 and 0 on the other and the neutral will see 20 amps. As you can see you will never see more than 20 amps. If both hot conductors were on the same phase then the Neutral current would be added. 20 amps on both then the Neutral would see 40 amps.... That's would be the problem


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## joe-nwt (Mar 28, 2019)

Dennis Alwon said:


> If the conductors are on different phase- usually next to each other- then the neutral will never seen more than 20 amps. The formula is N = Line 1- Line 2
> 
> put 20 amps on both hot conductors and the neutral will read 0-- strange but true.
> 
> Put 20 amps on 1 and 0 on the other and the neutral will see 20 amps. As you can see you will never see more than 20 amps. If both hot conductors were on the same phase then the Neutral current would be added. 20 amps on both then the Neutral would see 40 amps.... That's would be the problem


Don't you find it odd you have to explain that to a journeyman electrician?


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## Easy (Oct 18, 2017)

Lets just say you have an old office building with a 120/208v 3 phase service. All of the branch circuits are multi wire and feed lights and receptacles for computers. No tie bars on any of the breakers.
A group of 15 scientist are working on a cure for the next pandemic and have not yet backed up their data and a breaker trips. At least 10 of them can still keep working until an electrician can schedule a time to come in and pull in two more neutrals after they back up their files. I only mention this goofy scenario because there are *lots of places* wired like this and we just need to be cautious of the hazards of involving shared neutrals.


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## Dennis Alwon (May 9, 2009)

joe-nwt said:


> Don't you find it odd you have to explain that to a journeyman electrician?


Joe, we all have different abilities. I have seen members that have master electrician and they ask some basic questions. Since I never had any electrical classes it was years later that I really understood this..actually it is still voodoo to me. BBQ or Bob Badger knew ever code backwards and forward but he couldn't spell.... I know that is not quite the same but you get my point. 

I learned many things throughout my years but it wasn't until later on that I really tried to understand the physics of it. I wired hundreds of homes some 12,000 sq. ft and more and never even look at a code book for years. It wasn't until 2006 or so that I started getting serious about the code. 

I had a learning disability thru my life and reading was very hard for me. I still tend to scan and miss things so I understand, usually when questions are asked that seem simple to me.


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## yankeejoe1141 (Jul 26, 2013)

kb1jb1 said:


> As for the notorious multiwire branch circuits what would you do? I went on a service call for a window AC unit tripping out the circuit breaker. When I took off the cover I noticed several multiwire circuits on twin breakers. The same twin breaker had both the black and red wire. It has been like that for over 20 years and the home owner is elderly and did not understand the problem. The white wire on one of them was brown. The choices were 1. Leave it alone and just fix what I was called for. 2. Put both black and red wires under the same breaker. 3. Keep the black on one leg and move the red to the other. There is no way for me to know where the other ends of the circuits are and there is a concern of sending 240 some where. I haven't used multiwire circuits for over 20 years because of the confusion it might cause down the road.


Which option did you go with? I see this same situation at times also, I usually go with option 1, even though most won't agree I figure that it hasn't failed yet and if I touch it, I own it. And I also don't want to be accused of fishing for add ons, trying to explain why it's wrong to a novice is hard, especially when they say "well it's been working for 20 years".

I remember going into a basement once with someone new who kept pointing out all sorts of things, I had to tell him focus on the task at hand, we're not here to re-wire the whole house.


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## kb1jb1 (Nov 11, 2017)

Easy said:


> Lets just say you have an old office building with a 120/208v 3 phase service. All of the branch circuits are multi wire and feed lights and receptacles for computers. No tie bars on any of the breakers.
> A group of 15 scientist are working on a cure for the next pandemic and have not yet backed up their data and a breaker trips. At least 10 of them can still keep working until an electrician can schedule a time to come in and pull in two more neutrals after they back up their files. I only mention this goofy scenario because there are *lots of places* wired like this and we just need to be cautious of the hazards of involving shared neutrals.


I like what you said about we need to be cautious around multiwire circuits. Years back I was working on a pull box with many circuits. As I was pulling out the wires the wire nut came off and the white wires separated. Fortunately nothing was on at the time.


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## kb1jb1 (Nov 11, 2017)

yankeejoe1141 said:


> Which option did you go with? I see this same situation at times also, I usually go with option 1, even though most won't agree I figure that it hasn't failed yet and if I touch it, I own it. And I also don't want to be accused of fishing for add ons, trying to explain why it's wrong to a novice is hard, especially when they say "well it's been working for 20 years".
> 
> I remember going into a basement once with someone new who kept pointing out all sorts of things, I had to tell him focus on the task at hand, we're not here to re-wire the whole house.


The multiwire circuit that had the white wire turn brown, I separated it. That one I know fed two dedicated AC receptacles. The others I left alone because of time constraints.


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## dspiffy (Nov 25, 2013)

Dennis Alwon said:


> Joe, we all have different abilities. I have seen members that have master electrician and they ask some basic questions. Since I never had any electrical classes it was years later that I really understood this..actually it is still voodoo to me. BBQ or Bob Badger knew ever code backwards and forward but he couldn't spell.... I know that is not quite the same but you get my point.
> 
> I learned many things throughout my years but it wasn't until later on that I really tried to understand the physics of it. I wired hundreds of homes some 12,000 sq. ft and more and never even look at a code book for years. It wasn't until 2006 or so that I started getting serious about the code.
> 
> I had a learning disability thru my life and reading was very hard for me. I still tend to scan and miss things so I understand, usually when questions are asked that seem simple to me.


I started with engineering classes long before I ever read a code book. The amount of code that has little or no bearing on science will hurt your head.


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## Greg Sparkovich (Sep 15, 2007)

LGLS said:


> Will be replacing a friend's panel in a week. Guess how many Arc-faults I'm installing in their 3 bedroom 1968 ranch?


All of them -if you want to be sure that there aren't any shared neutrals (_especially_ on the same pole) and you care enough about your friend/they can afford it. I use AFCIs as a diagnostic tool for just this reason (all the houses I work on are 1880s-1920s, lots of K&T, so I laugh at your dates).


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## Greg Sparkovich (Sep 15, 2007)

yankeejoe1141 said:


> Which option did you go with? I see this same situation at times also, I usually go with option 1, even though most won't agree I figure that it hasn't failed yet and if I touch it, I own it. And I also don't want to be accused of fishing for add ons, trying to explain why it's wrong to a novice is hard, especially when they say "well it's been working for 20 years".


It's easy to make a drawing of a straight line (Neutral), a wave that intersects the line (Hot), and then another wave that is 180 out of phase (another Hot). That shows how a neutral is shared by trading between the 2 hots.
But what if both of the hots were on the neutral at the same time and pushing twice the amount of electricity that the neutral was designed to handle? Do you think that might be a reason for the wire to burn up? 

All of us should know this:
Don't be afraid of your customers or what they "might" think. Be the expert who is on THEIR side.

A simple explanation like the one above gets you gratitude (you're a hero to every mother of a child in that house!), loyalty, a 5-star review wherever they found you, and more business than you can handle.
And yeah, every one of my reviews is 5-stars or "A" rating on every site I'm on. Which means I never pay for advertising, only work within 20 minutes of my house, don't take jobs I don't like, never work 40 hours a week, am booking into September for people who want to wait that long...and I charge whatever I want (including that I can afford to do charity work and not worry about how much time it takes).
_Everybody_ hates hiring contractors; be the contractor people like and trust. If/when the next guys comes in and explains what you left undone, your name is going to be ****-posted all over the internet.


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## just the cowboy (Sep 4, 2013)

I had an EC come in and do work in our lab one time, panel replacement. It was all 3 phase MWBC, he landed all the hots and was going to land all the neutrals, after lunch. A lab boss asked if he could power everything up while he was at lunch. EC took all neutrals and twisted them together and just jammed them under main neutral lug and powered up and went to lunch. Whole thing popped out of lug creating open neutral and crazy voltage to a about 42 circuits in a lab. SMOKE , POOF, FLASH $300,000 just like that.

Cowboy


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## Easy (Oct 18, 2017)

just the cowboy said:


> I had an EC come in and do work in our lab one time, panel replacement. It was all 3 phase MWBC, he landed all the hots and was going to land all the neutrals, after lunch. A lab boss asked if he could power everything up while he was at lunch. EC took all neutrals and twisted them together and just jammed them under main neutral lug and powered up and went to lunch. Whole thing popped out of lug creating open neutral and crazy voltage to a about 42 circuits in a lab. SMOKE , POOF, FLASH $300,000 just like that.
> 
> Cowboy


Computers and electronics hate open or floating neutrals. That guy really took a financial beating. I wonder if his insurance would even cover something like that.
I'm not sure about the rest of you guys but I personally land my grounds, then my neutrals and finally my hots. I do the same in reverse when I demo circuits.


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## just the cowboy (Sep 4, 2013)

Easy said:


> Computers and electronics hate open or floating neutrals. That guy really took a financial beating. I wonder if his insurance would even cover something like that.
> I'm not sure about the rest of you guys but I personally land my grounds, then my neutrals and finally my hots. I do the same in reverse when I demo circuits.


He was fired for it, turns out he was a drinker.


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## 460 Delta (May 9, 2018)

just the cowboy said:


> I had an EC come in and do work in our lab one time, panel replacement. It was all 3 phase MWBC, he landed all the hots and was going to land all the neutrals, after lunch. A lab boss asked if he could power everything up while he was at lunch. EC took all neutrals and twisted them together and just jammed them under main neutral lug and powered up and went to lunch. Whole thing popped out of lug creating open neutral and crazy voltage to a about 42 circuits in a lab. SMOKE , POOF, FLASH $300,000 just like that.
> 
> Cowboy


Ouch, but really, how long would it have taken to just land 12 neutrals on a neutral bus? By the time he skinned 12 wires and twisted them together in some fashion, then crammed them in a big lug, he could have about done it right.
Likely was getting the shakes and couldn’t think clearly.


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## Easy (Oct 18, 2017)

just the cowboy said:


> He was fired for it, turns out he was a drinker.


That was common years ago. Lot's of people I worked with came to work drunk. Some of the workers had stashes of alcohol they would hide at strategic locations throughout plant. The executives had mini bars in their offices. 50% of the desks had ash trays because smoking was common place. Things sure have changed.


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