DERATING OF CONDUCTORS

[scotty]

I JUST READ MIKE'S QUESTION, AND I WAS IN THE PROCESS OF MINE. WHEN WE FEED ARE WIRES FROM A SINGLE PHASE PANEL 240/120 DO WE NEED TO COUNT THE NEUTRALS? ARE WE ABLE TO HAVE 9 12AWG HOTS AND 9 NEUTRALS AND BE FUSE AT 20 AMPS? OR 8 12AWG
HOTS AND 4 NEUTRALS AND BE FUSE AT 20AMPS? I UNDERSTAND ABOUT HARMONICS AND THERE IS NONE ON THESE CIRCUITS AND THREE PHASE WYE CONNECT SYSTEMS. I'VE READ THE HANDBOOK AND WOULD LIKE TO KNOW IF THE IS A BETTER WAY TO UNDERSTAND THESE CODE RULES!! :roll:

 

[russ]

Re: DERATING OF CONDUCTORS

310.15(B)(4)(a)-(b)and(c).

Nine circuit conductor and nine grounded conductors is 18 conductors.

120/240 single phase:
Eight circuit conductors each neutral conductor shared between a pair of A&B phase conductors, with mostly linear loads, equals 8 conductors. 310.15(B)(4)(a)

120/208 3phase
Eight circuit conductors each neutral conductor shared between an A&B phase, B&C phase or C&A phase conductors, even with mostly linear loads, equals 12 conductors.310.155(B)(4)(b)

 

[dnbob]

Re: DERATING OF CONDUCTORS

Basically the only time that you do not have to count the neutrals is on a 120/240 v. 3 wire circuit. (two hots on opposite phases sharing one neutral) (single phase)
-------------------------------------------------
If you have a 3 wire circuit on 120/208 v. 3 phase then you will always count neutrals.

If you have a 4 wire circuit from a 120/208 v. 3 phase source, then only if the "major portion" of the loads are nonlinear, (mostly computers & fluorescent lights, then you would count the neutrals. If you have, say incandescent lights, or gen. purpose receptacles then you would not have to count your neutrals.