Low Voltage Cable Ampacity with Four or More Conductors in Rigit Galvanized Steel Conduit

The allowable ampacity of four or more low voltage conductors in isolated rigid galvanized conduit in air can be practically determined from ICEA S-135 if the cables are identical. The National Electrical Code (NEC) has been used to determine the derated ampacity of four or more low voltage conductors in conduit, but the theoretical or empirical basis for the derating factors is not contained or referenced in the NEC.