What should the total ampacity consideration be for continuous loads on a circuit?

When dealing with continuous loads in an electrical circuit, the total ampacity should be considered at 80% of the circuit’s maximum capacity. This guideline arises from the National Electrical Code (NEC), which defines continuous loads as those that operate continuously for three hours or more.

The reasoning behind the 80% rule is to provide a safety margin that accounts for the potential heat buildup and to ensure the conductors are not overloaded. By using only 80% of the ampacity of the circuit components, including wires and breakers, the electrical system is less likely to experience overheating, potentially leading to failures or fires. This conservative approach is critical for maintaining a safe and reliable electrical installation.

If the load were to be calculated at 100% of the circuit’s capacity, it would leave no headroom for variations in load dynamics, increases in demand, or other unforeseen factors, which could pose significant safety risks. Therefore, utilizing 80% as the guideline maximizes safety while ensuring that the circuit performs effectively within its designed limits.