Conductor Ampacity and Voltage Drop Calculator

Circuit type

Module/string Isc (A)

One-way length (ft)

System voltage (V)

Max voltage drop target

Conductor material

Insulation rating

Ambient air temp

Current-carrying conductors in raceway

Conduit run on or above a rooftop (310.15(B)(3)(c) adder)

Recommended size

Corrected ampacity

Voltage drop

Size	Corrected ampacity	Ampacity ok	VD percent	VD ok

Base ampacity from NEC Table 310.16, DC resistance from Chapter 9 Table 8 (uncoated), two-way voltage drop. PV source/output circuits apply Isc x 1.25 (690.8(A)(1), irradiance factor) x 1.25 (690.8(B)(1), continuous duty) = 1.5625x. Ambient correction uses sqrt((Tc-Ta)/(Tc-30)) so the rooftop adder stacks precisely. Educational estimate only, not a substitute for a licensed engineer's stamped design.