Which two currents must be calculated to size overcurrent protection devices correctly?

To size overcurrent protection devices correctly, it's essential to consider both load current and potential fault currents. Load current represents the normal operational load that the circuit is expected to carry under typical conditions. This helps ensure that the overcurrent protection device is adequately sized to handle the ongoing demands of the connected load without tripping unnecessarily.

Potential fault currents, on the other hand, are critical to assess because they represent the maximum current that could flow in the event of a fault, such as a short circuit. The overcurrent protection device must be capable of interrupting this high fault current without failure to ensure safety and protect the circuit and connected equipment. Proper calculation of these two types of currents allows for the selection of an overcurrent protection device that not only protects normal operational conditions but also handles extreme fault situations, thereby preventing equipment damage and enhancing safety.