NEC Commercial Electrical Practice Test

What must happen to the ampacity when the number of current-carrying conductors in a raceway exceeds allowable limits?

1. It must be increased

2. It must remain the same

3. It must be reduced

4. It must be doubled

The correct answer is: It must be reduced

When the number of current-carrying conductors in a raceway exceeds allowable limits, the ampacity must be reduced to prevent overheating and ensure safety. This is due to the heat generated by the current flowing through the conductors; as more conductors are placed in a confined space like a raceway, the heat dissipation is decreased. The National Electrical Code (NEC) outlines specific derating factors that must be applied when the number of conductors exceeds certain thresholds. This means that when multiple conductors are grouped together, their individual ampacities can be compromised due to the cumulative heat they produce. By reducing the ampacity, the system can operate safely within thermal limits, helping to prevent failure, fires, or other hazards that might arise from overheating. Understanding this requirement is crucial for electrical installations and ensuring compliance with safety standards in the NEC.