215.4(A) Feeders with Common Neutral Conductor.

[unsaint34]

215.4 Feeders with Common Neutral Conductor.
(A) Feeders with Common Neutral. Up to three sets of 3-wire feeders or two sets of 4-wire or 5-wire feeders shall be permitted to utilize a common neutral.

I don't get it. Let's say my building needs 20 circuits for lights (277V). So, according to the article, I can only run two sets of 4-wire feeders for the total of 6 circuits, and for the remaining 14 circuits, I have to run 14 neutral wires with 14 ungrounded wires. What am I not understanding? Thanks for any help.

 

[kwired]

215.4 Feeders with Common Neutral Conductor.
(A) Feeders with Common Neutral. Up to three sets of 3-wire feeders or two sets of 4-wire or 5-wire feeders shall be permitted to utilize a common neutral.

I don't get it. Let's say my building needs 20 circuits for lights (277V). So, according to the article, I can only run two sets of 4-wire feeders for the total of 6 circuits, and for the remaining 14 circuits, I have to run 14 neutral wires with 14 ungrounded wires. What am I not understanding? Thanks for any help.

That section is talking about feeders, I think you are trying to apply it to branch circuits.

 

[infinity]

Think of a 1? riser where you will tap off of it on three floors. You run 2 phase conductors to each floor and a common neutral for all three floors. This is common in apartment buildings.

 

[unsaint34]

As you can guess, I am not the smartest electrician when it comes to NEC, but I am trying to be better at it.

Let me just clarify the language of this article here. First of all, when I hear the term "4-wire," for example, I assume three ungrounded and one neutral wire. So, when I hear "two sets of 4-wire can utilize a common neutral," I am picturing set A and set B, each set containing three ungrounded wires and one neutral wire. So, I understand the code as saying the set A's ungrounded conductors can use the set A's neutral wire (and the set B's ungrounded conductors can use the set B's neutral wire).

Did I get this right so far?

 

[Dennis Alwon]

As you can guess, I am not the smartest electrician when it comes to NEC, but I am trying to be better at it.

Let me just clarify the language of this article here. First of all, when I hear the term "4-wire," for example, I assume three ungrounded and one neutral wire. So, when I hear "two sets of 4-wire can utilize a common neutral," I am picturing set A and set B, each set containing three ungrounded wires and one neutral wire. So, I understand the code as saying the set A's ungrounded conductors can use the set A's neutral wire (and the set B's ungrounded conductors can use the set B's neutral wire).

Did I get this right so far?

Yes, but for feeders not branch circuits. It is clear in the 2011 that an oversized neutral for more than 3 CCC is no longer acceptable.-- 200.4

 

[Dennis Alwon]

but I am trying to be better at it.

That is the important part- it ain't easy and even the experts do not agree.

 

[unsaint34]

My guess for this restriction's intention --> the chance of unbalanced phase loading is higher on the feeder circuits than the branch circuits. Is it right?


To me, maximum of 5 multiwire feeder circuits for a huge building sounds not enough. But the more I think of it, one multiwire feeder circuit does not mean it feeds one subpanel. I guess, the multiwire feeder circuit can go to multiple sub-panels via a gutter.


Thanks a lot for feedback/education.

 

[darekelec]

rule

rule

so what is the rule of calculating the size of neutral wire? if i have for example 3 apartments fed by 60 amp single phase feeders?how do i size now the common neutral?

 

[Dennis Alwon]

so what is the rule of calculating the size of neutral wire? if i have for example 3 apartments fed by 60 amp single phase feeders?how do i size now the common neutral?

You would do a load calculation based on the 120V loads or any neutral loads connected to that feeder. Look at 220.61

 

[Smart $]

As you can guess, I am not the smartest electrician when it comes to NEC, but I am trying to be better at it.

Let me just clarify the language of this article here. First of all, when I hear the term "4-wire," for example, I assume three ungrounded and one neutral wire. So, when I hear "two sets of 4-wire can utilize a common neutral," I am picturing set A and set B, each set containing three ungrounded wires and one neutral wire. So, I understand the code as saying the set A's ungrounded conductors can use the set A's neutral wire (and the set B's ungrounded conductors can use the set B's neutral wire).

Did I get this right so far?

Yes, but for feeders not branch circuits. It is clear in the 2011 that an oversized neutral for more than 3 CCC is no longer acceptable.-- 200.4

I don't believe that's quite right. For two sets of 4-wire with common neutral there would be a total of 7 wires... two sets of three ungrounded and one common neutral.