wire gauge?

System
System Posts: 2,511 admin
in General Solar Power Topics #1
trying to figure out what gauge of wire to use running from a bank of 4 s460's to a 3524 panel...any suggestions are appreciated...shane
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #2
    Re: wire gauge?
    cdncam wrote: »
    trying to figure out what gauge of wire to use running from a bank of 4 s460's to a 3524 panel...any suggestions are appreciated...shane

    Use the voltage drop calculator listed in this post:
    http://forum.solar-electric.com/showthread.php?t=29

    http://www.uwgb.edu/nevermab/voltage_drop_calculator_.xls
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  • crewzer
    crewzer Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
    #3
    Re: wire gauge?

    Here’s my take on this question using the 2005 US National Electrical Code:

    (1) NEC 690.8(A)(4): maximum inverter current = ((3500 VA / 85% efficiency) / 21 VDC min) = 196 A.
    (2) NEC 690.8(B)(1): Conductors and overcurrent protection devices must be rated for 125% of maximum current, so 196 A x 125% = 245 A.
    (3) Recommended DC input breaker is 250 A, which is next standard size up from 245 A; looks OK to me.

    (4) Wire ampacity based on conditions of use (inverter max power spec based on 25 C ambient):
    (a) 90 C wire corrected for 25 C ambient and two conductors run in conduit between battery box and breaker panel: Ampacity requirement = 250 A / 1.05 = 238 A; 4/0 AWG wire (260 A) meets requirement per NEC 310.16.
    (b) 90 C wire corrected for 25 C ambient, derated for 75 C breaker terminal spec and “free air” (not in conduit) connection to breaker: Ampacity requirement = 250 A / 1.05 = 238 A; 2/0 AWG wire (265 A) meets requirement per NEC 310.17.
    Worst case condition of use is (a), so 4/0 wire is required. Looks like this is in agreement with recommendations from OutBack forum.

    HTH,
    Jim / crewzer
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