i screwed this up, so you probably should skip to the next message, but i'll leave it here in case someone wants to see what's wrong with it
i think you just have to do both calculations because voltage drop will have different reductions than derating reductions.
430.6 >>> table 430.150 >>> 52a
since fedup started with #3 i assume this is single motor each b.c. so..
430.22(A) says to use 125% of flc for continuous duty from T430.150
430.22(E) uses other than 125% if not continuous duty so it could be different here
430.150 >>> 52a FLC
430.22 >>> 52x1.25= 65a
310.13 assuming 350 ft is underground or piped underground so it's wet >>> xhhw/90*C
310.16 >>> 6awg Cu
Chapter 9 Table 9 6awg Cu in pvc
is .49ohms/1000ft but upsized once to 4awg is .31ohms/1000ft
for 6awg Cu:
L-N drop [.49] [350ft/1000] [65] = 11.15v
L-L drop [11.1475] [1.732] = 19.3v
19.3v/480v = 4% is more than the fpn 3%/b.c.
for 4awg Cu:
L-N drop [.31] [350ft/1000] [65] = 7.05v
L-L drop [7.0525] [1.732] = 12.21v
12.21v/480v = 2.5% is less than the fpn 3%.
210.19 fpn4 says 3% is ok for VD on bc's
so 480v x .03 = 14.4v would be an allowable VD for this b.c. using 4awg Cu..... but if you use 3+ bundled wires then adjustment factors are more restrictive than VD.....
using 70% from Table 310.15(B)(2)(a) Adjustment Factors for More Than Three Current-Carrying Conductors in a Raceway or Cable.......
75*C column wire for 6awg is 65amps, so..
[.7] [65] = 45.5amps is the adjusted maximum ampacity for 6awg. too low, we need 65amps [to meet the 52amps x 1.25, per 430.22]
75*C column wire for 4awg is 75amps, so....
[.7] [75] = 52.2amps, still too low.
75*C column wire for 3awg is 100amps, so..
[.7] [100] = 70amps is ok.
90*C column wire for 4awg is 95amps, so..
[.7] [95] = 66.5amps, also works.
so my choice is 4awg Cu XHHW [ok to use 90*C column at 95amps if underground], or in a dry location then XHHW-2 at 90*C
[This message has been edited by Cindy (edited 11-16-2002).]
