When is a neutral a current carrying conductor for 3 phase systems

[jar546]

Is there a difference between 3 phase services and 3 phase circuits?

When does the neutral count as a current carrying conductor for service entrance cable?

 

[rnapier]

1) There are differences in how the codes apply but there is no differences in the electrical principles.

2) Always and would be sized according to these sections.

230.23 Size and Rating and 230.31 Size and Rating.

© Grounded Conductors. The grounded conductor shall

not be less than the minimum size as required by

250.24©.

250.24©.

(1) Sizing for a Single Raceway. The grounded conductor

shall not be smaller than the required grounding electrode

conductor specified in Table 250.66 but shall not be required

to be larger than the largest ungrounded serviceentrance

conductor(s). In addition, for sets of ungrounded

service-entrance conductors larger than 1100 kcmil copper

or 1750 kcmil aluminum, the grounded conductor shall not

be smaller than 121⁄2 percent of the circular mil area of the

largest set of service-entrance ungrounded conductor(s).

230.42 Minimum Size and Rating.

(A) General. The ampacity of the service-entrance conductors

before the application of any adjustment or correction

factors shall not be less than either 230.42(A)(1) or

(A)(2). Loads shall be determined in accordance with Part

III, IV, or V of Article 220, as applicable. Ampacity shall be

determined from 310.15. The maximum allowable current

of busways shall be that value for which the busway has

been listed or labeled.

(1) The sum of the noncontinuous loads plus 125 percent

of continuous loads

 

[Gregg Harris]

I think he is asking if a three phase service is required to have a neutral, and does a three phase circuit require a neutral.

And when is a neutral considered to be a current carrying conductor, is a clear question.

 

[raider1]

Is there a difference between 3 phase services and 3 phase circuits?When does the neutral count as a current carrying conductor for service entrance cable?

Are you asking when a neutral counts as a CCC for ampacity adjustments?

Chris

 

[markw]

3 p. service-weatherhead to meter/panel/dissconnect

3 p. circuit-overcurrent protection device to final receptacle/appliance/etc...

neutral is the grounded conductor-used to calculate load,carrier of the current between phases

 

[gfretwell]

The neutral needs to be brought to the service disconnect if this is a wye or center tapped delta but it does not need to go beyond that if there is no neutral load.

Things get a little different if this is a corner grounded delta since the grounded conductor is not really a neutral, although you still identify it with white.

Then there is ungrounded delta but that is not very common in most venues.

 

[Uncle Bob]

nec 310.15 b?

 

[Gregg Harris]

310.15 (B) (4) (a) (b) ©

(5) Neutral Conductor

(a) A neutral conductor that carries only the unbalanced current from other conductors of the same circuit shall not be required to be counted when applying the provisions of 310.15(B)(3)(a).

(b) In a 3-wire circuit consisting of two phase conductors and the neutral conductor of a 4-wire, 3-phase, wye-connected system, a common conductor carries approximately the same current as the line-to-neutral load currents of the other conductors and shall be counted when applying the provisions of 310.15(B)(3)(a).

© On a 4-wire, 3-phase wye circuit where the major portion of the load consists of nonlinear loads, harmonic currents are present in the neutral conductor; the neutral conductor shall therefore be considered a current-carrying conductor.

 

[BSSTG]

The neutral needs to be brought to the service disconnect if this is a wye or center tapped delta but it does not need to go beyond that if there is no neutral load.Things get a little different if this is a corner grounded delta since the grounded conductor is not really a neutral, although you still identify it with white.

Then there is ungrounded delta but that is not very common in most venues.

Greetings,

I've been an electrician for almost 40 years and I recall a corner grounded delta only 1 time in the Houston area. I do recall seeing a few ungrounded deltas way back when.

BSSTG

 

[jar546]

Are you asking when a neutral counts as a CCC for ampacity adjustments?Chris

Yes I am. That is the point of my post but of course I rushed to get this posted this morning.

 

[gfretwell]

A place I saw corner delta was sewer lift stations. The main load is a big 3p pump and then a controller that is L/L across 2 of the phases.

They end up using equipment that looks exactly like a single phase service with 2 ungrounded conductors and a white grounded conductor.

It just needs to be rated for 240 delta.

It is confusing the first time you see one.

 

[Dennis]

It would be a rare situation where the neutral would count on a 3 phase wye system. If 50% + of the loads are nonlinear then it would count but this is usually only found in computer areas . Generally florescent lights are nonlinear , although the newer electronic ones are not so bad, but that would not usually count for more than 50%-- perhaps in an unheated warehouse it would be

 

[north star]

# = = = #

markw,

Welcome to the Building Codes Forum !

# = = = #

 

[gfretwell]

Back in the olden days when we really had computers (not a rack full of PCs) we did not even extend the neutral into the computer room. Everything was L/L or 3p