I'm working on figuring a neutral calculation for a 120/208 volt 400 amp feeder. I have looked through the code , but i think i have confused myself more than any thing. Does #3 neutral sound correct? I'm pulling 500 kcmil to the Sub panel and #3 just seems small . Thx
Neutral Calculations
- Thread starter mavrck
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So I’m little confused. I understand you have to figure you loads for the neutral but why wouldn’t you just use this table if that works? I think that’s my confusion.
And does any wye connected neutral have be sized the same as the ungrounded conductors or is it only the 3 wire getting fed from a wye. 220.61c1
And does any wye connected neutral have be sized the same as the ungrounded conductors or is it only the 3 wire getting fed from a wye. 220.61c1
- Location
- New Jersey
- Occupation
- Journeyman Electrician
We very rarely see reduced size neutrals in feeder conductors for panels but they are permitted. As Augie stated the neutral is sized based on the calculated neutral load but cannot be smaller than in your case #3 AWG.
Because in that 3-wire circuit the neutral can carry current equal to that of the ungrounded conductors.
Because in that 3-wire circuit the neutral can carry current equal to that of the ungrounded conductors.
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
Yes that would be the case. In residential it is common to see the neutral sized one size down from the hot conductors because there are usually many 240 volt circuits without, or with limited use, neutral current.
- Location
- New Jersey
- Occupation
- Journeyman Electrician
IMO yes unless unknown means that there is no neutral load at all and just a feeder to a panel. Then you could use the minimum size.
- Location
- Illinois
- Occupation
- retired electrician
You need to look at the 120 volt loads to do the neutral calculation. The more 120 volt loads you have on a single phase, the larger the neutral has to be.
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