All Neutrals together multi-circuit

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Cletis

Senior Member
Location
OH
I've been noticing over the years in commercial and industrial facilities the placing of ALL the neutrals under 1 wirenut ?? Where there are say 3 or more circuits in a jbox, whether it be multiwire circuits or just multiple circuits (3 phase and Single Phase) someone got in there and modified and just put all the neutrals under 1 nut. I have several questions about this illegal act.

Why would someone do that?

What actually happens to the current path back to the panel ? (which path does the current take ?)

Does the current return path generally balance out back to panel via less resistance ?

Why is this dangerous or is it ?

I've seen it done alot and generally never observe burnt or browning neutrals at jboxes or at the panel neutral/ground bar either.

I was told by many old timers that this "Balances the Load" Any thoughts on this too ?
 

kwired

Electron manager
Location
NE Nebraska
Answers to questions within the quote:
I've been noticing over the years in commercial and industrial facilities the placing of ALL the neutrals under 1 wirenut ?? Where there are say 3 or more circuits in a jbox, whether it be multiwire circuits or just multiple circuits (3 phase and Single Phase) someone got in there and modified and just put all the neutrals under 1 nut. I have several questions about this illegal act.

Why would someone do that? They don't know any better.

What actually happens to the current path back to the panel ? (which path does the current take It takes all connected paths,

Does the current return path generally balance out back to panel via less resistance ? If all paths are same impedance (same size and length) then they will generally balance out.

Why is this dangerous or is itI can't absolutely say it is dangerous, but it certainly doesn't comply with parallel conductor rules if less then 1/0AWG conductors are involved. It effectively is creating a MWBC with parallel conductors for the neutral.

I've seen it done alot and generally never observe burnt or browning neutrals at jboxes or at the panel neutral/ground bar either. And I wouldn't expect to see those issues - open one conductor back to the source and you just increase the current on the others so if you had three conductors carrying total of say 30 amps - that would be 10 amps each lose one and you raise the current in the remaining two to 20. If it were a 30 amp multiwire circuit (I used this value for simplicity of calculations more then real world applications) you are not overloading the remaining conductors.

I was told by many old timers that this "Balances the Load" Any thoughts on this too ?It does, so does a traditional MWBC with a single neutral but uses less copper.
 

Cletis

Senior Member
Location
OH
Great. Let me throw out 1 real world example below in the 2 scenarios

Ex. 1
2 - 3 pole breakers (3p) each having their own neutral going to a jbox for branch cir distribution
The jbox would have 6 circuits, 2 main neutrals kept seperate to 3 branch neutrals. So 4 neutrals on 1 wirenut and 4 neutrals on another. Lets say cir 1,2,3 (1st 3 pole breaker) is A=14 amps, B=13 amps, C=18 amps. Lets say 2nd 3 pole breaker is following A=17 amps, B=8amps, C=15amps. It would be nice if someone felt like figuring out neutral current ? If not, no big deal.

Here is the big question of the day. In the ex. above if you keep neutrals seperate v.s. putting neutrals "all together" would the return current balance out better in the legal way or illegal method ??
 

rlundsrud

Senior Member
Location
chicago, il, USA
So you are saying they ran seperate neutrals for each circuit, then someone modified that by connecting all them together?

I suppose that you are effectively creating a parallel set for the neutral, which while completely against code for parallel conductors as they aren't large enough to parallel, should still work. I am not saying it's right, just that it should work as a single neutral for a MWBC. I assume they put a common tie on the breaker that feeds it (JK).

As to the path the electricity takes in a parallel system, it takes all of them regardless of the impedance.

As to the "balances the load" part, that to me is the same mentality as electricity only takes the path of least resistance. I hear some old timers spouting that litany fairly often as well.

*I should have waited, the previous posters pretty much summed it up.
 

Cletis

Senior Member
Location
OH
So you are saying they ran seperate neutrals for each circuit, then someone modified that by connecting all them together? YES

I suppose that you are effectively creating a parallel set for the neutral, which while completely against code for parallel conductors as they aren't large enough to parallel, should still work. I am not saying it's right, just that it should work as a single neutral for a MWBC. I assume they put a common tie on the breaker that feeds it (JK). NO, not usually

As to the path the electricity takes in a parallel system, it takes all of them regardless of the impedance.

As to the "balances the load" part, that to me is the same mentality as electricity only takes the path of least resistance. I hear some old timers spouting that litany fairly often as well.

*I should have waited, the previous posters pretty much summed it up.

I would love to do a real world experiment with this if I can find the time with a clamp meter, this would probably be much simplier.

What I"m asking in scenario 1 (legal way) say you have 8 amp on neutral 1 and 6 amps on neutral 2, if you put them all together will you get less say 4 amps and 4 amps or something like that ?
 

kwired

Electron manager
Location
NE Nebraska
I would love to do a real world experiment with this if I can find the time with a clamp meter, this would probably be much simplier.

What I"m asking in scenario 1 (legal way) say you have 8 amp on neutral 1 and 6 amps on neutral 2, if you put them all together will you get less say 4 amps and 4 amps or something like that ?
It depends on impedances of each path, but if we assume each neutral is same size, length, and has other similar conditions that effect impedance - then each path will have equal impedance and current will divide evenly among all paths. End up with one conductor that has significantly lower impedance for some reason and it may carry the bulk of all current, but the other paths will still carry some current.
 
The main danger with shared neutrals from separate circuits is working on a circuit that you have de energized and not realizing that it shares neutral with one serving a load.

I know that's only a very small part of your question
 

Cletis

Senior Member
Location
OH
The main danger with shared neutrals from separate circuits is working on a circuit that you have de energized and not realizing that it shares neutral with one serving a load.

I know that's only a very small part of your question

Yes, valid point but this question is not about safety. It's highly unsafe to those who don't know what they are doing. In example above there is not a 6 pole handle tie so someone not familiar could get hurt pretty bad. I'm just concentrated on how the return current balances out in this thread.
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
Two reasons it happens:

1) A guy who doesn't know much reasons that because all the neutrals are tied together on the neutral bar, it's okay to tie them together at a junction box. In a lot of cases this has no consequences but it matters when working on circuits or modifying them, or if the neutrals happen to go back to different places or through different raceways.

2) The original installers don't group and mark the circuits, and when someone else comes along and modifies or services them he either forgets to mark them before he disconnects stuff, or he has no way of telling to begin with. And it would take him more hours to trace the circuits than the rest of his job is supposed to take. So he reverts to the logic of reason (1) and either figures it's someone else's problem or he'll wait to deal with it if/when he has to.

I thought that there was a code section that requires the conductors of each circuit to be grouped (unless otherwise indicated by where they enter and exit). But I can't find it right now. Anyone know?

As far as consequences, lots and lots of potential variations, but I think they would all come down to 3 categories:

1) An electrician getting shocked when he removes a neutral termination that's supposedly for a circuit he turned off, and it turns out that neutral is also energized from a different circuit.

2) Losing track of neutrals for MWBCs, along with losing track of MWBCs themselves, and thus putting the hots for MWBCs on the same phase and charring the neutrals. I deal with this problem frequently when trying to make space for an additional breaker.

3) Inductive heating because not all the neutrals follow the same raceway back to the same panel and thus neutral current is travelling in a different raceway than the ungrounded conductor.
 

donaldelectrician

Senior Member
As to the why would some one do that ?


The only time I have seen that done throughout the job was an eye opener for me . They were installing Energy Management Systems in chain stores throughout the Country . They modified the correct wiring on all the lights and neutrals were mixed up everywhere after they installed there equipment .

It is a Safety Issue . When i see a system in a chain store now , I know what to expect .




Don
 

kwired

Electron manager
Location
NE Nebraska
If there are neutrals returning to the source(s) via multiple raceways or cables it would allow for more hazards then it would for just multiple neutrals in same raceway that are tied together. If all in same raceway they have better chance of being roughly same impedance and will result in nearly balancing load across all of them. You still need to turn off every circuit involved before opening those neutrals though or you will have backfeed voltage that will wake you up when you open the connection and happen to contact those exposed conductor ends.
 

kwired

Electron manager
Location
NE Nebraska
Two reasons it happens:

1) A guy who doesn't know much reasons that because all the neutrals are tied together on the neutral bar, it's okay to tie them together at a junction box. In a lot of cases this has no consequences but it matters when working on circuits or modifying them, or if the neutrals happen to go back to different places or through different raceways.

2) The original installers don't group and mark the circuits, and when someone else comes along and modifies or services them he either forgets to mark them before he disconnects stuff, or he has no way of telling to begin with. And it would take him more hours to trace the circuits than the rest of his job is supposed to take. So he reverts to the logic of reason (1) and either figures it's someone else's problem or he'll wait to deal with it if/when he has to.

I thought that there was a code section that requires the conductors of each circuit to be grouped (unless otherwise indicated by where they enter and exit). But I can't find it right now. Anyone know?

As far as consequences, lots and lots of potential variations, but I think they would all come down to 3 categories:

1) An electrician getting shocked when he removes a neutral termination that's supposedly for a circuit he turned off, and it turns out that neutral is also energized from a different circuit.

2) Losing track of neutrals for MWBCs, along with losing track of MWBCs themselves, and thus putting the hots for MWBCs on the same phase and charring the neutrals. I deal with this problem frequently when trying to make space for an additional breaker.

3) Inductive heating because not all the neutrals follow the same raceway back to the same panel and thus neutral current is travelling in a different raceway than the ungrounded conductor.
200.4(B) in 2014 NEC was expanded from previous requirements to include separate identification or grouping so that it is apparent which grounded conductor goes with which ungrounded conductors and must be done in pretty much all raceways, cables or enclosures now. Before it was just required to do so in cases like multiple multiwire circuits to help identify which multiwire circuit the grounded conductor went with.

Since we are in this area of the NEC 200.4(A) specifically prohibits installing per the topic of this thread.
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
Since this is a commercial job we are talking ferrous raceways, I assume, therefore art. 300.3 (B). This section also comes into [play since the neutrals will have a parallel path so that all neutral current is going everywhere. This could potential overload a neutral, create electromagnetic field's - lets not go there- and heat up the conduits.
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
In the example you gave there is 4.58 amps on neutral cir#1 and 8.19 on cir 2. Of course this depends on the fact that the circuits are constant. There is no way to determine how much is going which way without more info. It will probably work fine but still a violation
 

charlie b

Moderator
Staff member
Location
Lockport, IL
Occupation
Retired Electrical Engineer
I have tried to sketch out the example described in post #3. I am not certain I have it right. But let me ask this: Suppose I designed a 3-pole MWBC to serve three single phase heaters located in three adjacent rooms. I leave the panel with 3 ungrounded wires, 1 grounded (neutral) wire, and 1 EGC. When I get to the first load, I need to connect 1 ungrounded wire, 1 neutral, and the EGC. Then I have to continue the run towards the next load. How do I do that? I have to imagine that there is a junction box in which I use a wire-cap to connect 3 neutral wires (the incoming, the one to the load, and the one that continues to the next load). How is that different from the example given in post #3? If I leave the junction box in three separate directions with three separate conduits going to the three loads, it seems to me that the only way to complete the circuit is to connect 4 neutral wires with a wire -cap, in exactly the manner described in the example. Why is this illegal? If a MWBC is legal, how else can it be wired, in the almost universal circumstance that the various loads are not immediately adjacent to each other? Other than my second cup of coffee this morning, what am I missing?:?
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
I have tried to sketch out the example described in post #3. I am not certain I have it right. But let me ask this: Suppose I designed a 3-pole MWBC to serve three single phase heaters located in three adjacent rooms. I leave the panel with 3 ungrounded wires, 1 grounded (neutral) wire, and 1 EGC. When I get to the first load, I need to connect 1 ungrounded wire, 1 neutral, and the EGC. Then I have to continue the run towards the next load. How do I do that? I have to imagine that there is a junction box in which I use a wire-cap to connect 3 neutral wires (the incoming, the one to the load, and the one that continues to the next load). How is that different from the example given in post #3? If I leave the junction box in three separate directions with three separate conduits going to the three loads, it seems to me that the only way to complete the circuit is to connect 4 neutral wires with a wire -cap, in exactly the manner described in the example. Why is this illegal? If a MWBC is legal, how else can it be wired, in the almost universal circumstance that the various loads are not immediately adjacent to each other? Other than my second cup of coffee this morning, what am I missing?:?

Charlie, he has 2 multiwire branch circuit each with 3 hots and a neutral then leaves that jb with 2 other circuits but the 4 whites are tied together from both 3 wire circuits from the panel.
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
200.4(B) in 2014 NEC was expanded from previous requirements to include separate identification or grouping so that it is apparent which grounded conductor goes with which ungrounded conductors and must be done in pretty much all raceways, cables or enclosures now. Before it was just required to do so in cases like multiple multiwire circuits to help identify which multiwire circuit the grounded conductor went with.

Since we are in this area of the NEC 200.4(A) specifically prohibits installing per the topic of this thread.

Thanks, that's what I was looking for.

Everyone really needs to follow this for the guy who comes after you, which often enough is yourself or someone working for you.
 

kwired

Electron manager
Location
NE Nebraska
I have tried to sketch out the example described in post #3. I am not certain I have it right. But let me ask this: Suppose I designed a 3-pole MWBC to serve three single phase heaters located in three adjacent rooms. I leave the panel with 3 ungrounded wires, 1 grounded (neutral) wire, and 1 EGC. When I get to the first load, I need to connect 1 ungrounded wire, 1 neutral, and the EGC. Then I have to continue the run towards the next load. How do I do that? I have to imagine that there is a junction box in which I use a wire-cap to connect 3 neutral wires (the incoming, the one to the load, and the one that continues to the next load). How is that different from the example given in post #3? If I leave the junction box in three separate directions with three separate conduits going to the three loads, it seems to me that the only way to complete the circuit is to connect 4 neutral wires with a wire -cap, in exactly the manner described in the example. Why is this illegal? If a MWBC is legal, how else can it be wired, in the almost universal circumstance that the various loads are not immediately adjacent to each other? Other than my second cup of coffee this morning, what am I missing?:?
I guess I don't know exactly what he has, but as I understand it he was describing it as though there were multiple neutrals pulled for a "home run" or even multiple "home runs" some installer just tied all of them together at any junction boxes in the run instead of keeping them isolated to the circuit they are supposed to go with. General operation wise - shouldn't even be noticed as long as no wire connectors end up coming loose. Still is in violation of 200.4(B) and can cause some shock hazards for someone working on this at some time if they don't realize what circuits all need to to be turned off before there is no risk of back feed voltage on an open neutral.
 

charlie b

Moderator
Staff member
Location
Lockport, IL
Occupation
Retired Electrical Engineer
Charlie, he has 2 multiwire branch circuit each with 3 hots and a neutral then leaves that jb with 2 other circuits but the 4 whites are tied together from both 3 wire circuits from the panel.
I don't think so, Dennis. I think he has two MWBCs that have no connection to each other. Here is how he describes it:
So 4 neutrals on 1 wirenut and 4 neutrals on another.
For each of the two separate MWBCs, you have one neutral leaving the panel connecting to three neutrals leaving in three separate directions. The fact that the two wire nuts, each connecting the 4 white wires from its own MWBC, are installed in the same junction box does not change the (apparent - to me at least - but I still may be missing something) fact that the two MWBCs are independent of each other.



 
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