Enter a wire's base ampacity, ambient temperature, and number of conductors bundled together to see its real derated capacity.
This uses standard NEC-style derating tables (simplified) — always verify against the current NEC and local code for a final design, especially for permitted installations.
A wire's ampacity rating from a standard table assumes a specific ambient temperature (typically 86°F) and free air with no other current-carrying conductors nearby — hot attics, conduit runs, and bundles of multiple circuits all reduce a wire's real-world safe capacity because heat can't dissipate as easily. This matters especially for solar combiner boxes and conduit runs across a hot rooftop, which routinely see both high ambient temperature and multiple conductors bundled together — cross-check the result against the wire gauge calculator if you're sizing from scratch rather than checking an existing run.
Rooftop-mounted conduit exposed to direct sun can reach ambient temperatures well above standard tables assume, sometimes requiring an additional temperature adder specified in the NEC beyond simple air temperature.
Often yes — if the derated ampacity falls below your circuit's required current, stepping up to a larger gauge (or reducing the number of bundled conductors) restores adequate capacity.