200.3

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hassaf

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I have a situation where we have panel A (3phase 4w) feeding panel B (3ph 3w), and panel B feeding another panel C (3ph 4w). Neutral for Panel C was connected to panel A neutral Bus, and routed from A via Panel B feeder conduit, then routed via Panel C feeder conduit to panel C. Does this installation violate NEC 200.3?

I tried to explain to inspector that this should be safe, since if someone turns off panel B feeder breaker (that is located in panel A), then the neutral in Panel A will be dead for Panel C. But the inspector is red tagging it since it voilate 200.3? Please advise.

My understanding of 200.3 is that it applies to utility supply, and that it is required that we have a neutral from utility that is solidly grounded.

Is there anywhere in the code that permit this installation?
 
lakee911 said:
Seems kind of an odd set-up. Was it accidentally done this way and you're trying to justify it or was this a design decision?

Thx,
Jason
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Panel B is located in an existing building that is served from panel A with 3ph 3w system @ 480, but we have a new 277V load in the building now, so we need a neutral, so we provided a new panel C 480/277V 3ph 4w, and we brought the neutral from source panel A.
 
hassaf said:
Panel B is located in an existing building that is served from panel A with 3ph 3w system @ 480, but we have a new 277V load in the building now, so we need a neutral, so we provided a new panel C 480/277V 3ph 4w, and we brought the neutral from source panel A.
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Okay. I see where you are coming from. Feeding panel C from panel A would have been a little more standard as would adding a transformer between B and C to get a nuetral, but it would be more expensive. I was thinking that adding the nuetral to panel B would also be acceptable, but that's essentially what you've done...minus the bus.
 
lakee911 said:
Okay. I see where you are coming from. Feeding panel C from panel A would have been a little more standard as would adding a transformer between B and C to get a nuetral, but it would be more expensive. I was thinking that adding the nuetral to panel B would also be acceptable, but that's essentially what you've done...minus the bus.
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That is correct. But the electrical sub-contractor was worried that if he added a neutral bus in panel B, that it would compromise the UL listing and name plate of that panel.

FYI...Panel A is 1200 Amp, panel B is 800 amps, panel C is 100 Amps.
 
Dennis Alwon said:
I am not sure this is an issue but 300.3(B) could be the code that is being violated.
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The neutral conductor is routed in the same raceway with the supply conductor from Panel A to panel B, and in the same raceway as supply conductors from Panel B to C.

I think this would be a voilation 300.3(B) if the neutral from Panel A is not in the same raceway as supply conductors to Panel B.

For Example, let say the neutral is routed in a separate raceway from A to B, then there no way to tell which breaker would make that particular neutral "dead". The only way to make that neutral dead is to turn off the entire panel A, or turn off all breakers. But since we have the neutral in same raceway, then you can tell which breaker is associated with which neutral since the "hot" conductors from the breaker is routed in same racway as neutral.
 
hassaf said:
The neutral conductor is routed in the same raceway with the supply conductor from Panel A to panel B, and in the same raceway as supply conductors from Panel B to C.

I think this would be a voilation 300.3(B) if the neutral from Panel A is not in the same raceway as supply conductors to Panel B.

For Example, let say the neutral is routed in a separate raceway from A to B, then there no way to tell which breaker would make that particular neutral "dead". The only way to make that neutral dead is to turn off the entire panel A, or turn off all breakers. But since we have the neutral in same raceway, then you can tell which breaker is associated with which neutral since the "hot" conductors from the breaker is routed in same racway as neutral.
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But, the neutral routed back to panel A that is with the conductors of A isn't part of the circuit that feeds panel A. The install should work when you turn it on, but it's a weird way of doing it. I can see a case for 300.3(B) but I'm new at this so there might be something I'm missing.
 
I agree with the Handbook narrative in that 200.3 deals with the connectikon of the premises wiring system to the utility supply and, to me, has nothing to do with internal wiring.

"Grounded conductors of premises wiring must be connected to the supply system (service or applicable separately derived system) grounded conductor to ensure a common, continuous, grounded system."
 
IF
All of the circuit conductors 'start' at Panel A.
As they leave, all of the conductors are contained in the same raceway.
The phase conductors are stopped at Panel B, where they are reduced in size (with proper protection).
The reduced size phase conductors and the neutral continue on to Panel C.

End result - any current flowing on a the neutral originated from a phase conductor located in the same raceway. Therefore there is no violation of 300.3(B).
 
jim dungar said:
IF
All of the circuit conductors 'start' at Panel A.
As they leave, all of the conductors are contained in the same raceway.
The phase conductors are stopped at Panel B, where they are reduced in size (with proper protection).
The reduced size phase conductors and the neutral continue on to Panel C.

End result - any current flowing on a the neutral originated from a phase conductor located in the same raceway. Therefore there is no violation of 300.3(B).
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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?
 
200.3

We do that all the time when we have 120/240 3ph4w stinger leg.

For example, when we have a 120/240 3ph4w service on site, we bring a 3ph 4w to a building on site from Main Switchboard to panel 'X' 3ph 3w, but we do not land the neutral in that panel, so no one can use it for 120V loads becuase of the liklehood of using the high leg with neutral, but rather, we would route the neutral thru the panel to another sub-panel 120/240 1ph 3w.

No one used to question this installation in the past, and it did not seem to be a contraversial issue at the time.

I could not find anything in the code that would prohibit this, but also, could not find anything that would allow it. but the inspector is hitting me over the head to find something in the code that would allow this.
 
bluesmoke...oops said:
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?
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The neutral would only carry the unbalanced loads of Panel C (100 Amps), I don't see why to oversize it for 800Amps. The breaker feeding panel C will open if there is is an oveload in access of 100Amps, and it would protect the neutral conductor from overloads.
 
hassaf said:
The neutral would only carry the unbalanced loads of Panel C (100 Amps), I don't see why to oversize it for 800Amps.
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I think good design practice in this case would be to size it for 800A between A and B and size it for 100A between B and C. Then, in the event that panel B is ever replaced with a 4W panel it would already be sized appropriately (in my opinion, full size is appropriate), or if someone comes along in the existing panel and decides to tap it for a 4W device, or feed another 4W panel, it would be of the correct size.
 
bluesmoke...oops said:
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?
Click to expand...
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)
 
lakee911 said:
I think good design practice in this case would be to size it for 800A between A and B and size it for 100A between B and C. Then, in the event that panel B is ever replaced with a 4W panel it would already be sized appropriately (in my opinion, full size is appropriate), or if someone comes along in the existing panel and decides to tap it for a 4W device, or feed another 4W panel, it would be of the correct size.
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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.
 
hassaf said:
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.
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Well, you do have to do what you have to do. :) You're lucky you could pull the wire into an existing filled conduit anyhow!

Jason
 
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