What does 'continuous load' mean and how does it affect protection sizing?

What does 'continuous load' mean and how does it affect protection sizing?

• A. A load that stops at regular intervals; it has no effect on protection sizing.
• B. A load expected to run for three hours or more; it affects the sizing and selection of overcurrent protection.
• C. A load that is intermittent; it decreases conductor gauge.
• D. A load that only runs during peak periods; it increases protection rating.

Answer: (B)

Continuous load is a load expected to operate for three hours or more. Because it runs for extended periods, the conductors and protection must be sized to handle the sustained current without overheating. That’s why protection sizing uses 125% of the continuous current—to provide a safety margin for heat buildup. In practice, you multiply the continuous current by 1.25 to find the minimum overcurrent protection rating (and then select a standard-size device at or above that value). For example, a 20 A continuous load needs at least 25 A protection (or the next standard size) and conductors with an ampacity of at least 25 A. This 125% rule mainly applies to continuous loads; noncontinuous loads don’t require that same margin, which is why the factor isn’t used for those.

Continuous load is a load expected to operate for three hours or more. Because it runs for extended periods, the conductors and protection must be sized to handle the sustained current without overheating. That’s why protection sizing uses 125% of the continuous current—to provide a safety margin for heat buildup. In practice, you multiply the continuous current by 1.25 to find the minimum overcurrent protection rating (and then select a standard-size device at or above that value). For example, a 20 A continuous load needs at least 25 A protection (or the next standard size) and conductors with an ampacity of at least 25 A. This 125% rule mainly applies to continuous loads; noncontinuous loads don’t require that same margin, which is why the factor isn’t used for those.