How is the allowable ampacity of each conductor affected in a raceway or cable with more than three current-carrying conductors?

The allowable ampacity of each conductor in a raceway or cable with more than three current-carrying conductors must be reduced to account for the increase in heat generated by the electrical current. This adjustment is necessary because when multiple conductors are bundled together, they can create a situation where they cannot dissipate heat effectively.

The National Electrical Code (NEC) stipulates that as the number of current-carrying conductors increases beyond three, a derating factor must be applied. This means that the ampacity of each individual conductor is decreased to ensure safe operation and to prevent overheating, which could lead to insulation failure or even fire hazards.

For example, if a raceway contains more than three conductors and each is rated for a certain current, the overall thermal conditions lead to a need to lower the effective current that each conductor can safely carry. Thus, recalibrating the ampacity based on the number of conductors in the raceway or cable is a critical practice in electrical installations to maintain safety and reliability.