Grounded Conductor Size Reduction

[rroark0003]

Guys,

I have heard that the neutral can be reduced 12.5% or 70% of the size of the ungrounded conductors. I'm not sure which is right or if either one is. My question is, on a 200 amp service using 4/0 aluminum ungrounded condutors would it be acceptable to use a 2/0 aluminum neutral conductor on a 120/240volt single phase service supplying a moblile home.

Thanks

 

[bphgravity]

Reduction of the Grounded (Neutral) conductor is based on calculation and not a vague rule of thumb. See Section 220.61 of the NEC.

 

[petersonra]

you can skip it altogether if you have no neutral current.

 

[Dennis Alwon]

you can skip it altogether if you have no neutral current.

Not for a service. A neutral must be supplied to the building.

There is a minimum size but as Bryan stated you must calculate the load. In most residential jobs there is the unwritten rule of reducing the grounded conductor by one size. Most services have many 240 volt loads and thus do not need a grounded conductor. This is where the reductions come into play.

 

[Pierre C Belarge]

Not for a service. A neutral must be supplied to the building.

There is a minimum size but as Bryan stated you must calculate the load. In most residential jobs there is the unwritten rule of reducing the grounded conductor by one size. Most services have many 240 volt loads and thus do not need a grounded conductor. This is where the reductions come into play.

250.24(C) in reference to the above post.

250.24(C)(1) for sizing in some applications or 220.61 as Bryan has mentioned.

 

[bphgravity]

Section 250.24(C) identifies the minimum...

 

[rroark0003]

The permitted reductions in Article 220.61 are dependant on a load calculation to determine the unbalance of load or the current that may be present in the neutral conductor. Is this correct?

Some SE and USE cables manufactures are reducing the neutral conductor to half the size of the ungrouded conductors without knowing the unbalance of the load.

 

[Dennis Alwon]

Some SE and USE cables manufactures are reducing the neutral conductor to half the size of the ungrouded conductors without knowing the unbalance of the load.

I have never seen an se cable with a neutral that was 1/2 the size. The grounding conductor may be based on 250.122 but not the neutral conductor. Here is a southwire chart

 

[miller2009]

CLARIFY ON 22.61(b)2

CLARIFY ON 22.61(b)2

Was looking for a little bit of help on permitted reductions of a nuetral conductor of a 3 phase system. Have a 1200 amp service with a 200,00 kw load of heating which comes out to 921 amps i think. Was just tryingto better understand that article because the inspector couldn't tell me wheter it was legal or not