When several AC, MC, or NMC cables are installed close together, how does it affect the current-carrying capacity of the conductors?

When multiple AC, MC, or NMC cables are installed in close proximity to one another, the current-carrying capacity of the conductors is reduced due to the phenomenon known as grouping or conduit fill effect. This occurs because the heat generated by each conductor can accumulate when cables are closely packed, leading to higher temperatures than those experienced by a single conductor operating alone.

As temperature increases, the resistance of the conductors also increases, resulting in a lower permissible current-carrying capacity in order to prevent overheating and potential damage. Therefore, when installing multiple cables together, engineers and electricians must reference ampacity tables and consider derating factors to ensure they do not exceed the reduced current-carrying capacity of the combined cables. This consideration is critical for maintaining safety and reliable operation of electrical systems.