Is it considered standard practice to permanently install a line fuse on the source side of an OCR under normal conditions?

The practice of permanently installing a line fuse on the source side of an Over Current Relay (OCR) is generally not considered standard practice because it can create unnecessary risks and complications. The primary function of an OCR is to monitor and detect overcurrent conditions to protect the circuit. Installing a fuse on the source side can prevent the OCR from performing its job effectively.

If a fault occurs downstream, the OCR is designed to trip and isolate the faulted section. However, if a line fuse is in place, it could potentially blow before the OCR can act, which could affect the overall protection coordination of the system. Additionally, in many regulatory standards and codes, equipment should be designed to allow for reliable operation without the interference of a fuse in that location.

In summary, the correct choice highlights the impracticalities and risks associated with such an installation under normal conditions, reinforcing safe and effective practices in electrical distribution systems.