Wire Sizing

Wire Sizing Intro

Wire Sizing

Solar Design Calculator: Calculate NEC-compliant wire sizes for PV source circuits and AC output circuits. Determine minimum conductor gauge with automatic temperature derating, conductor bundling adjustments, terminal temperature limits, and OCPD selection. Ensures compliance with NEC 690.8, 310.15, 240.4(D), and 110.14(C) for safe solar installations.

Circuit Configuration
PV uses Isc x 1.56 / AC uses Imax x 1.25
Isc for PV circuits / Imax for AC
How strings are connected
Environmental Conditions (COU)
Installation environment (10-50C)
Total in raceway (min 2)
Equipment terminal rating
THWN-2 90C insulation
Minimum Wire Size
-
OCPD Rating
-
Imax (Max Current)
-
Icont (Continuous)
-
Derated Ampacity
-
FIRST CHECK: Continuous Load (Steps 1-5)
-
SECOND CHECK: Conditions of Use (Steps 6-10)
-
NEC Compliant
Wire size meets all NEC requirements including 690.8 (PV), 240.4(D) (OCPD limits), 310.15 (temperature/bundling), and 110.14(C) (terminals).
About 10-Step NEC Wire Sizing
Steps 1-5 determine base ampacity using Icont (PV: Isc x 1.56, AC: Imax x 1.25) for terminal and OCPD checks. Steps 6-10 apply COU deratings using Imax (PV: Isc x 1.25, AC: Imax) to verify derated ampacity. PV circuits use 156% (1.25 x 1.25) per NEC 690.8(B)(1) for continuous loads, while AC uses 125% per standard continuous load rules.