200 amp 3 phase 4 wire delta 120/208/240 - wire size

Status
Not open for further replies.
J

Jamespcboyd

Member
Location
California
Occupation
Training
What is the proper size of wire? For a roughly 6 ft run I'm torn between 3/0 and 4/0.. between the ambient temperature and the fact you could possibly or could not possibly account for the neutral as a conductor.. THHN or XHHW-2.. of course it has to be sized for the temperature of 75C.. hottest ambient temperature of 106.. Just Need a secondary Opinion?
 
95% of the time here it would be 3/0 with no questions but the devil is in the details.
The 106 ambient isn't going to make much difference, brings the 3/0 to just under 200 amps.
So few services that size actually have a major portion of the load as non-linear the neutral rarely counts as a current-carrying conductor.
IF the neutral is counted 40 /wound be required, For a 6 ft run, if it was questionable, I'd run 4/0 rather than have to show calculations.
 
For a Delta system would you ever count the neutral as a CCC for derating purposes?
 
augie47 said:
95% of the time here it would be 3/0 with no questions but the devil is in the details.
The 106 ambient isn't going to make much difference, brings the 3/0 to just under 200 amps.
Click to expand...

To add onto this, the reason why you commonly can still accept an ampacity that is slightly less than 200A, is that 240.4(B) likely can apply. The wire needs to have enough ampacity for the calculated load, and "round up" to the 200A rating.
 
infinity said:
For a Delta system would you ever count the neutral as a CCC for derating purposes?
Click to expand...

If the line-to-neutral loads on the A-N-C winding were harmonic-intensive, and in particular contained even harmonics, then yes. The line-to-line loads and three phase loads that don't touch the neutral wouldn't make a difference.

Unlike wye systems where triplen harmonics are the ones that accumulate on the neutral, even harmonics are what will accumulate on the neutral in a 120/240V split phase system, or the A-N-C winding of a high leg system.
 
So basically all that's 3 phase on this property is the water well... and a large air compressor... the rest is lighting, swamp coolers, ac units, hand held power tools, 2 pole air compressors, and welders.. some 110 welders.. lighting is florescent.. which is being changed to led... very little computer equipment.. Don't know how the 200 amp delta service appears to be for the most part under utilized.. Of Course it's never all on at once.. in this case would the neutral count as a conductor? Cause the way its written in the NEC confuses me a little..
 
Neutral need not ce counted as a CCC.

Best way to utilize the high leg is to use it for L-L loads that don't need the neutral.
 
Man without this forum I would be lost! I want to thank all of you for replying.. I try to use common sense for all wiring.. and then I read the nec code.. it confuses my common sense factor.. thank you all
 
There is nothing in 310.15(B)(5) that would require you to count the neutral as a CCC in a Delta system.

310.15(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).
(c) 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.
Click to expand...
 
Status
Not open for further replies.
Top