Branch Circuit Neutrals

[ryguy1116]

I have a question in regards to neutral distribution.

I have a 400VAC(pri)/230VAC(sec) 5kva transformer.

The "hot" line goes to a distribution block and then is distributed to 4 branch circuits each branch circuit is protected with a 10A circuit breaker.

The neutral is grounded then goes to a distribution block.

Is it ok to isolate each branch circuit with its own neutral?

The intent is not to overload the neutral and be forced into running a larger gauge wire. Each branch neutral line would be identified with a specific branch tag and specific wire #.

Example:
The first branch circuit "CB1" would be identified as "Control #1 (#1)". It's neutral would be identified as "Control Neutral #1 (#1A)"

The second branch circuit "CB2" would be identified as "Control #2 (#2)". Its neutral would be identified as "Control Neutral #2 (#2A)".

Is this addressed in NEC?

 

[wareagle]

The neutral from the transformer must be sized to hanfle the max unbalanced load. Each ckt must have it own
neutral and connected to the main neutral from the transformer. I am not sure what you mean by isolate.
"Is it ok to isolate each branch circuit with its own neutral?"

 

[rbulsara]

If you mean running "separate" neutral conductor for each branch circuit, but connected to a common neutral block/bus at the distribution block, then the answer is Yes.

The word isolation could be misleading.

 

[waross]

Are you in the UK or EU? The answer may be different in North America. The neutrals are defined differently.
respectfully.

 

[EEJaime]

I assume you are merely wishing to run individual branch circuit neutrals in lieu of running a four-wire branch circuit feed wherein three circuits share a neutral. If that is the case then you are perfectly ok doing so. We have used this as our standard design for several years now as the office/school/hospital environments have become heavily laden with switched power supplies, electronic ballasts, etc.... As you mentioned this eliminates the need for oversizing branch neutrals, but it does increase the amount of wire used in a building.

You should also get a read from your local AHJ as to how they consider this application insofar as wire count. Does your 3/4" conduit with three circuits now have SIX current carrying conductors? Will instances occur where you have to derate your conductors due to wire counts? If so this may not be the cost saving item you might have thought. But it will work fine.

Best,

Jaimexx

 

[waross]

Are you using 115/230 volt circuits, or 230 volt circuits?
115/230 volt circuits have a neutral conductor which in NEC land must also be the grounded conductor. One common neutral may serve two circuits of opposite polarity. The neutral does not need to be larger than the circuit conductors.

If you are using 230 volts from a 230 volt transformer then you don't have a neutral. You may have a grounded circuit conductor but it is not a neutral. It must have the same ampacity as the "Hot" wire. I don't think that the code expressly addresses the case of multiple two wire circuits using a common grounded circuit conductor. (Note: The grounded circuit conductor is NOT the grounding conductor. It is usually but not always the neutral.)
If you do use a common grounded circuit conductor it will the return for 4 x 10 amp circuits and should have an ampacity of 40 amps.
respectfully