200.3

[Smart $]

Install a neutral bus in Panel 'B'. Then take the neutral from the bus in 'B' and supply 'C'. No one will have issues at this point, although I do not see an issue with the install as described by the OP.

While installing a neutral bus in panel B would solve one [pseudo]problem, it may create a real problem if the panel marking says 3? 3W.

I too see no problem with the install as described.

 

[hassaf]

While installing a neutral bus in panel B would solve one [pseudo]problem, it may create another if the panel marking says 3? 3W.

I too see no problem with the install as described.

The name plate indicate 3ph 3w

 

[hurk27]

I have always thought all conductors have to originate from the same panelboard?

210.4 address branch circuit conductors, but I can't find this for feeders?

If this is true, then the neutrals for panel C can't feed from panel A if panel C ungrounded conductors are fed from panel B?

 

[Pierre C Belarge]

The name plate indicate 3ph 3w

I thought that what paint is for.....:roll:

 

[hassaf]

I have always thought all conductors have to originate from the same panelboard?

210.4 address branch circuit conductors, but I can't find this for feeders?

If this is true, then the neutrals for panel C can't feed from panel A if panel C ungrounded conductors are fed from panel B?

That's true for branch circuits. You cannot connect the hot for lights or receptacle from one panel 'x' and neutral from a different panel 'y', and especially if both panels are fed separatly from a switchboard. Beacuse you can turn panel 'y' off, but one of the neutrals in panel 'y' is still hot and have 120V.

 

[curt swartz]

Is there only a single raceway between Panel A and Panel B or are there multiple raceways with parallel conductors?

 

[hassaf]

Is there only a single raceway between Panel A and Panel B or are there multiple raceways with parallel conductors?

parallel raceway/conductors

 

[jim dungar]

I have always thought all conductors have to originate from the same panelboard?

I am always amazed at how much stuff "I remember wrong".:grin::roll:

 

[curt swartz]

parallel raceway/conductors

If you only installed a neutral in one of the raceways between A and B you would not comply with 310.4(C)

 

[hassaf]

If you only installed a neutral in one of the raceways between A and B you would not comply with 310.4(C)

this might be a voilation (I'm not sure), but this neutral is not part of the parallel conductors to panel B!! My understanding of intent of Parallel conductors is to have to same impedence (conductors have to be same number & length), and the additional neutral will not affect the current balance in both parallel runs.

What if we install 1 #2 AWG (for panel C neutral) in each conduit from A to B, and join them together in Panel B, and run (1) #2 (panel C neutral)from B to C.

 

[kwired]

But isn't there current flowing due to other things in that panel? So doesn't that mean that the neutral would have to be sized according to the "circuit" in which it is was run with? Otherwise you are running a neutral sized for a 100A circuit in with a 800A circuit.

I don't see them being on the same circuit in this case. If they are the same circuit, then wouldn't the neutral need to be sized properly?

Absolutely the neutral needs to be sized correctly, just like the phase conductors need to be. The code requirement is to size the neutral to carry the unbalanced loading. The NEC clearly allows the neutral to be a different size than the phase conductors. Also, there is no requirement that a neutral conductor be terminated anywhere it is not being used (service equipment does require the grounded service conductor to be terminated)

215.2(A)(1) requires minimum size of grounded conductor in a feeder circuit to be sized to 250.122.

For the 800 amp feeder that means a minimum size of 1/0 copper. After panel "B" it can be reduced to as small as 8 AWG if there is no more load than 8 AWG will carry.

You want your grounded conductor to be able to carry any faults imposed on it without compromising the conductor just like you would with an equipment grounding conductor.

 

[Smart $]

this might be a voilation (I'm not sure), but this neutral is not part of the parallel conductors to panel B!! My understanding of intent of Parallel conductors is to have to same impedence (conductors have to be same number & length), and the additional neutral will not affect the current balance in both parallel runs.

What if we install 1 #2 AWG (for panel C neutral) in each conduit from A to B, and join them together in Panel B, and run (1) #2 (panel C neutral)from B to C.

It is a violation of 310.4(B) [2008]. Each conductor must be paralleled.

(B) Conductor Characteristics. The paralleled conductors
in each phase, polarity, neutral, grounded circuit conductor,
or equipment grounding conductor shall comply
with all of the following:
(1) Be the same length
(2) Have the same conductor material
(3) Be the same size in circular mil area
(4) Have the same insulation type
(5) Be terminated in the same manner

If you already have a #2 in one conduit, a #2 in the other would be the wiser choice IMO. As kwired posted:

215.2(A)(1) requires minimum size of grounded conductor in a feeder circuit to be sized to 250.122.

For the 800 amp feeder that means a minimum size of 1/0 copper. After panel "B" it can be reduced to as small as 8 AWG if there is no more load than 8 AWG will carry.

You want your grounded conductor to be able to carry any faults imposed on it without compromising the conductor just like you would with an equipment grounding conductor.

However, the grounded conductor is not subject to 250.122(F), so you do not have to run a 1/0 in each conduit. Yet the Code does not provide a designated method for splitting a grounded conductor's size into two equivalent-ampacity conductors (i.e. 250.122 specifies size based on ocpd rating, not ampacity). If we use 110.14(C) 75?C termination temperature limitations as the basis, you would have to run two #4 at a minimum... so two #2 should suffice.

 

[acrwc10]

It is a violation of 310.4(B) [2008]. Each conductor must be paralleled.

​

If you already have a #2 in one conduit, a #2 in the other would be the wiser choice IMO. As kwired posted:

​

However, the grounded conductor is not subject to 250.122(F), so you do not have to run a 1/0 in each conduit. Yet the Code does not provide a designated method for splitting a grounded conductor's size into two equivalent-ampacity conductors (i.e. 250.122 specifies size based on ocpd rating, not ampacity). If we use 110.14(C) 75?C termination temperature limitations as the basis, you would have to run two #4 at a minimum... so two #2 should suffice.

Except you can not run parallel conductors unless they are 1/0 or larger. 310.4(A)

 

[acrwc10]

I don't see an issue with NOT landing the neutral in panel "B" but you are stuck as far as being code compliant, you say #2 AWG is the largest conductor you are allowed in each conduit without over filling and 1/0 AWG is the smallest you can parallel. I think it is time to actually look at the size of the wire (cross sectional mils.) and do the math to see is you can get away with it, possibly use a compact conductor to get a little extra out of it. Good luck. OR since the inspector only wants the neutral landed in panel "B" and he obviously isn't a member here, Well Ya might get away with a little, uh, HACK work :roll: (I am just kidding, do it right or don't do it at all)

 

[Smart $]

Except you can not run parallel conductors unless they are 1/0 or larger. 310.4(A)

...but what about....

Exception No. 2: Under engineering supervision,
grounded neutral conductors in sizes 2 AWG and larger
shall be permitted to be run in parallel for existing
installations.

 

[hassaf]

...but what about....

I think that would work. Thanks!!!

 

[acrwc10]

Hassaf,
What is the conduit size, type and what are the conductors type and their sizes? Just so we can have a little more fun with it.

 

[kwired]

this might be a voilation (I'm not sure), but this neutral is not part of the parallel conductors to panel B!! My understanding of intent of Parallel conductors is to have to same impedence (conductors have to be same number & length), and the additional neutral will not affect the current balance in both parallel runs.

What if we install 1 #2 AWG (for panel C neutral) in each conduit from A to B, and join them together in Panel B, and run (1) #2 (panel C neutral)from B to C.

The neutral between A and B is carrying unbalanced current from a breaker in panel B (the one that feeds panel C) it is part of the feeder circuit. A neutral bus does not necessarily need to be installed in panel B. I would use Polaris or other similar connectors unless you see the need for future neutral loads from panel B

I agree that feeder conduit between A & B should have been designed with provisions to add a neutral conductor, and the feeder conduits should have been sized accordingly. But in our case we have existing conduits & feeders that are sized for three conductors and a ground between A & B, and we can barely fit another conductor (#2 AWG) for panel C without going over conduit fill limit. Otherwise, we would have to provide new 800 Amp feeder conduit between A & B.

A possibility if you have metal raceways is to use the raceway as the equipment ground and the old grounding conductor for the neutral. There have been threads on this with a lot of debate over whether or not this would be a good idea. Only you can see the condition of the raceways and have an idea of whether or not they are electrically continuous (which they are supposed to be anyway), and decide if this is a good idea.

 

[hassaf]

The neutral between A and B is carrying unbalanced current from a breaker in panel B (the one that feeds panel C) it is part of the feeder circuit. A neutral bus does not necessarily need to be installed in panel B. I would use Polaris or other similar connectors unless you see the need for future neutral loads from panel B



A possibility if you have metal raceways is to use the raceway as the equipment ground and the old grounding conductor for the neutral. There have been threads on this with a lot of debate over whether or not this would be a good idea. Only you can see the condition of the raceways and have an idea of whether or not they are electrically continuous (which they are supposed to be anyway), and decide if this is a good idea.

Yes. You're right. And I like your idea about the grounding conductor, but we do not have a grounding conductor, they're already using the conduit for that.

The distance between A & B approx 600ft, 3" Metal Codnuit -(3) #600 MCM, with no grounding conductor. The load in panel C approx 45Amps, and it looks like we can add up to 250 MCM, but I do not think that they can pull it all the way thru becuase of age of feeder. we do not care about future capacity at this point, next guy who comes in, or the next project they do, will have to replace this feeder.

It seems that a #2 in both conduit is the most correct approach at this point.

 

[hassaf]

Yes. You're right. And I like your idea about the grounding conductor, but we do not have a grounding conductor, they're already using the conduit for that.

The distance between A & B approx 600ft, 3" Metal Codnuit -(3) #600 MCM, with no grounding conductor. The load in panel C approx 45Amps, and it looks like we can add up to 250 MCM, but I do not think that they can pull it all the way thru becuase of age of feeder. we do not care about future capacity at this point, next guy who comes in, or the next project they do, will have to replace this feeder.

It seems that a #2 in both conduit is the most correct approach at this point.

Correction: 60ft not 600ft