When a branch circuit powers continuous loads, what must the rating of the overcurrent device accommodate?

The correct answer is that the rating of the overcurrent device must accommodate the noncontinuous load plus 125% of the continuous load. This requirement is vital for ensuring safety and preventing the overcurrent device from tripping under normal operating conditions.

When dealing with branch circuits that supply continuous loads, it’s crucial to recognize that continuous loads are those that are expected to operate for three hours or more. If an overcurrent device were to trip due solely to the draw from these loads, it could lead to an interruption in critical services or processes that rely on continuous power.

By specifying that the overcurrent device must be rated for the noncontinuous load plus 125% of the continuous load, the NEC ensures that there is adequate capacity to handle the continuous draw without nuisance tripping. This provision effectively allows for the continuous operation of devices without risking an overload and accommodates any potential inrush or transient currents that may occur when equipment is first powered on.

In essence, this approach prioritizes system reliability and safety, making it clear that care must be taken to accommodate both continuous and noncontinuous loads in the sizing of overcurrent protection devices.