What is the calculation for determining the required fuse size?

The correct choice represents the proper approach to sizing a fuse in electrical systems. Determining the required fuse size involves calculating the maximum current that will flow through the circuit under normal operating conditions. This is foundational to ensuring that the fuse can handle the expected load without blowing or tripping unnecessarily.

In the correct calculation, the factor of 1.25 is applied to account for the continuous loading of the circuit. This factor is significant because it allows for a safety margin above the normal operating current to handle transient conditions and ensure reliable operation. Specifically, using 1.25 helps to ensure that the fuse can tolerate brief overloads that may occur during startup or other peak usage scenarios without blowing prematurely.

By utilizing the formula given in the correct choice, which divides the product of 10 and 1000 (representing a power or load value) by 7960 (which is likely a constant relevant to the specific parameters of the system), and then multiplying by 1.25, you arrive at a fuse size that effectively balances safety and functionality. This approach safeguards both the equipment and the overall integrity of the electrical system during operation.