Individual Branch Circuit

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ken44

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I am putting together an estimate to provide a customer in a commerical building with 8 IBC's, they will be NEMA 5-20's originating from a 120/208 volt, 3 phase panel, there is an existing conduit that may be able to handle these 8 IBC's depending on the answer to this question, does each circuit have to have its own neutral wire or can 3 circuits share 1 neutral and still be considered as an IBC? IMO, if multiple circuits are sharing a neutral, I have a multi-wire branch circuit. I have looked at a bunch of the post under this subject but did not find an answer my question.
 
Call them what you will. You can have all three phase ungrounded conductors to one Neutral. If you are not sure, oversize the neutral.

8 circuits in a pipe...watch 310.15(B)(2)(a).
 
This is more of a theory question than a NEC question. Think of eight rooms, in a group on one side of a building and think of the supply panel being on the other (far) side of the building with only a single conduit running between the panel and a junction box located in the vicinity of the four rooms. Each room is provided 120 V receptacles and 120 V lights on an individual branch circuit.

Instead of sending the homerun of the individual branch circuit, on its own, all the way to the panel on the other side of the building, the installing electrician goes first to the local j-box on the end of the conduit run.

In the j-box, the electrician connects the individual branch circuits together to form 208/120 V 3? MWBCs. In so doing, s/he reduces the number of neutrals, reducing the current carrying conductor count, and reducing the number of wires for conduit fill.

The rooms are wired as individual branch circuits. The circuit path between the panel overcurrent protective device and the first outlet is broken into two parts. The MWBC part has a neutral that carries the unbalance current of the hot conductors, and the voltage drop along the circuit resistance is reduced.

The scenario I describe above has all 120 V loads on individual branch circuits. . . .there are no 208 V, 208/120 V or 3? loads.

The presence of the MWBC in a portion of the homerun between the OCPD and the first outlet on the individual branch circuit is a design consideration only. If, after derating for current carrying conductors in a raceway, and the sizing of the conductor for any other concerns, this portion of the path that is multiple MWBCs still squeezes into the existing conduit, then, hey! . . . good on ya! :smile:
 
Yes IMO each circuit of a MWBC can be an IBC based in the NEC.

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210.4 Multiwire Branch Circuits.
(A) General. ​
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Branch circuits recognized by this article
shall be permitted as multiwire circuits. A multiwire circuit
shall be permitted to be considered as multiple circuits.
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Branch Circuit, Individual.​
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A branch circuit that supplies
only one utilization equipment.​

 
Twoskinsoneman said:
Branch Circuit, Individual.
A branch circuit that supplies
only one utilization equipment.​
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Nicely done, Twoskins.

I'm hung on the petard of Article 100, again. I'd edit out some of the "individual" in my post above, if the privilege hadn't timed out.

My point, I think, remains still clear enough.

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Thanks for the input but this brings up another question, what are you calling current carrying conductors, I have been taught to only consider the hot's as current carrying conductors for derating purposes, if I do it that way then I can run #10 THHN and meet the derating and conduit-fill requirements.
 
I agree with the others that per the NEC you could call them individual branch circuits. However if this meets the customers expectations is another mater all together.

Don't forget a common disconnecting means for these circuits at the panel.
 
Whether the neutral counts as current carrying or not depends on the nature of the load (linear vs non-linear) {See 310.15(b)(4) }

If you don't need to count the neutrals, you should be able to use #12 THHN even with derating for 8 circuits..
 
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One thing you might want to keep in mind is that if you are under the 08 Code those MWBC will require common disconnect. You may still meet the literal definition of individual, but your customer may be disappointed when he needs to turn off one circuit (or one trips) and he looses three.
 
As a fan of MWBC's, I agree with the others. If I were doing this job, I'd run three 4-wire MBC's and reserve the 9th hot wire as a spare. Better to pull it in with the others now.
 
ericsherman37 said:
The original job was for 8 circuits... two full boat MWBCs and one 3 wire one... or just pull three full boat MWBCs and have a spare hot left over. Right? One extra wire?
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Sorry it WAS a stupid question and I was thinking the senario was different...I don't know what I was thinking...something about adding a two wire circuit and having to pull a neutral putting the count over the limit or something....Sorry please disregard the stupid question.
 
iwire said:
I agree with the others that per the NEC you could call them individual branch circuits. However if this meets the customers expectations is another mater all together.

Don't forget a common disconnecting means for these circuits at the panel.
Click to expand...

And that tie handle just might break the camels back. Individual has just been joined.
 
ericsherman37 said:
The original job was for 8 circuits... two full boat MWBCs and one 3 wire one... or just pull three full boat MWBCs and have a spare hot left over. Right? One extra wire?
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Right, and the loaded neutral would take the place of the unused conductor as the 9th CCC.
 
LarryFine said:
Right, and the loaded neutral would take the place of the unused conductor as the 9th CCC.
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Until someone came along and used the spare hot - at which point the neutral would only be carrying unbalanced load and wouldn't be a CCC for the purposes of adjustment factors.. am I correct? (Still learning this stuff too :smile:)
 
ericsherman37 said:
Until someone came along and used the spare hot - at which point the neutral would only be carrying unbalanced load and wouldn't be a CCC for the purposes of adjustment factors.. am I correct? (Still learning this stuff too :smile:)
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That's correct, 310.15(B)(4).
 
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