Xantrex Technology PV100S-480 - Manual (Page 46)

Planning
2–12 152315 Rev C
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 347 amps, it can be calculated that the required cable ampacity at
50 °C in this application is 423 amps. (347 divided by 0.82)
In this example, two cables per phase termination are used, so from NEC
Table 310.16 (Ninth Edition) it is apparent that the 90 °C THHN cable must be
3/0 AWG or larger. Two each 3/0 AWG conductors at 50°C have an allowable
ampacity of 450 amps (225 multiplied by 2).
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, 3/0 AWG, 2000 V cable is selected for the
AC Phase connections:
DLO 3/0 AWG Cable:
3/0 AWG DLO, 2000V, 90 °C per Phase
3/0 AWG has an O.D. of 0.789
0.789 x 0.789 x 6 x 0.7854 = 2.93 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:
2.93 + 0.250 + 0.058 = 3.238 in²
Using the "Over 2 Wires" column per NEC Chapter 9, Table 4, (Ninth Edition)
indicates that the following minimum permitted conduit trade size is acceptable
for the 15 wires in this exercise:
EMT = 3" Trade size
IMC = 3.5" Trade size
RMC = 3.5" Trade size