Page 91
©
2017 Sensata Technologies
Appendix D – Sizing Worksheet
b)
Find the PV circuit’s conductor size after derating factors have been applied:
Look at Table 310.15(B)(16) and select the insulation temperature rating column that corresponds to the lowest
temperature rating of any terminal the conductor is terminated on, regardless of the insulation of the selected
conductor. Select the smallest conductor that exceeds the derated current (I
DERATE
) calculation from Step 3a.
PV circuit derated current:
PV
SOURCE
-l
DERATE
=
PV
OUTPUT
-l
DERATE
=
Temperature rating of selected conductor:
(AWG @Temp)
(AWG @Temp)
Lowest terminal temperature:
Conductor sized after derating factors:
(AWG @Temp)
(AWG @Temp)
Step 4)
Determine the minimum required conductor size:
Compare the conductor sized to the continuous current (Step 2b) against the conductor sized after derating
factors (Step 3b); the largest conductor size between the two is the minimum required conductor.
Conductor Sized to the Continuous
Current (AWG @Temp):
Conductor Sized after Derating
Factors (AWG @Temp):
Minimum Required Conductor
Size (AWG @Temp):
PV
SOURCE
-l
CONT
=
PV
SOURCE
-l
DERATE
=
PV Source =
PV
OUTPUT
-l
CONT
=
PV
OUTPUT
-l
DERATE
=
PV Output =
Step 5)
Size the Overcurrent Protection Device (OCPD) to protect the selected conductor:
Ensure the size of the OCPD is equal to or greater than the Continuous Current (Step 2) and equal to or less than
the ampacity of the Minimum Required Conductor (Step 4) using a commonly available size (NEC Article 240.6).
Continuous Current
(l
MAX
x 125%):
Minimum Required Conductor:
Size of the Overcurrent
Protection Device (OCPD)*
(l
MAX
x 125%)
Size (AWG @
Temp)
Ampacity
**PV
SOURCE
-l
CONT
=
PV
OUTPUT
-l
CONT
=
*If the OCPD is rated for 100% operation, then it can be sized to the lower l
MAX
current (Step 1).
**The OCPD for each PV source conductor cannot exceed the “Series fuse” listed on the module label.
Note:
Consult manufacturer for OCPD rating if exposed to temperatures greater than 40°C.