With a fault occurring, which device should be the first to isolate the fault?

• A. Sectionalizer
• B. Recloser
• C. Fuse
• D. Circuit Breaker

Answer: (C)

When a fault happens on a distribution line, the first device to isolate the fault is placed right at the fault location and is designed to clear quickly and permanently. A fuse cutout serves this purpose: it carries normal load but blows open in the presence of fault current, removing just the faulty section from service. This fast, local action minimizes damage to equipment downstream and confines the outage to the smallest possible area.

Upstream devices like reclosers are used to restore service after transient faults by attempting to reclose, or to coordinate protection over a larger area. A sectionalizer helps segment the network but does not clear the fault by itself. A circuit breaker can protect the system, but it typically sits farther from the fault and would clear a larger portion of the network or require additional steps to isolate only the faulted section.

So, the fuse is the best first element to isolate the fault because it provides immediate, selective, permanent isolation right at the fault.