Xantrex Technology PV225S-480-P - Manual (Page 46)

Planning
2–12 152606
Step 3. Size the cable.
This example assumes that the conduit length is less than 24 inches. NEC
Table 310.16 (Ninth Edition) indicates the Temperature Correction Factor for
90 °C THHN cable in a 50 °C ambient is 0.82. With a required ampacity from
Step 1 above of 780.6 amps, it can be calculated that the required cable ampacity
at 50 °C in this application is 952 amps. (780.6 divided by 0.82)
In this example, four cables per phase termination are used, so from NEC Table
310.17 (Ninth Edition) it is apparent that the 90 °C THHN cable must be
262 kcmil or larger. Four each 262 kcmil conductors at 50°C have an allowable
ampacity of 984 amps (246 multiplied by 4).
Step 4. Size the conduit.
In this step, the cross sectional area of all the individual cables is first calculated.
Once calculated, the total cross sectional area of the cables is determined by
summing their values. In this example, 262 kcmil DLO, 2000 V cable is selected
for the AC Phase connections:
DLO 262 Phase Cable:
262 MCM DLO, 2000V, 90 °C per Phase
262 MCM has an O.D. of 0.973
0.973 x 0.973 x 12 x 0.7854 = 8.923 in²
Ground Cable:
1 Each #2 AWG (per NEC Table 250.122 (Ninth Edition),
using 400 A Breaker)
#2 AWG has an O.D. of 0.384 for THHN and 0.565 for DLO
0.565 x 0.565 x 0.7854 = 0.250 in²
Sense/Control Wires:
8 Each #16 AWG, UL1015, THHN, Hook-up Wire
#16 AWG has an O.D. of 0.096
0.096 x 0.096 x 8 x 0.7854 = 0.058 in²
Total:
DLO 262 Phase Cable = 8.923 in² (8.923 divided by 2 = 4.46)
Ground Cable = 0.250 in²
Sense/Control Wires = 0.058 in²
2 runs of conduit between the Isolation Transformer (T6-X1, T6-X2, and T6-
X3) and the Main Inverter Enclosure (TB5, TB6, and TB7)
1st conduit run; 4.46 + 0.25 = 4.71 in²
2nd conduit run; 4.46 + 0.058 = 4.52 in²