Generally, the Art. 210 requirements for branch circuits are prerequisites for applying requirements found elsewhere. This fact is exemplified by the overcurrent protection requirements [Sec. 210.20]. These focus on characterizing and calculating the load, something you must do before sizing the overcurrent protection devices (OCPDs) and conductors.
A continuous load is one that can be expected to operate three hours or more [Art. 100]. Lighting (for example) is a continuous load, unless there are specific circumstances such as controls that prevent it from ever operating continuously.
You don’t have to apply the “125% rule” to an assembly (including the OCPD) that’s listed for operating at 100% of its rating. But for branch circuits, apply the 125% rule. Here’s how:
- Identify which loads are continuous.
- Add them up and multiply by 125%.
- Add to that sum the total of the noncontinuous loads [210.20(A)].
Use the resulting number to size the branch circuit OCPD. But make sure the OCPD will protect the conductors against overcurrent in accordance with their ampacities per Sec. 310.15, except where Sec. 240.4 overrides that. For flexible cords apply the requirements of Sec. 240.5.
You may have to move some loads to other circuits, because the OCPD rating can’t exceed the rating specified in:
- The applicable Article(s) in Table 240.3 for equipment.
- Table 210.21 for devices.
