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Question

An industrial panel uses a cartridge fuse rated at 250V, 32A. If a technician replaces it with a 16A fuse of the same voltage rating, what is the likely outcome during normal operation at 28A?

This question was previously asked in
RRB NTPC 2025 Graduate Level CBT 1 Question Paper (25-Mar-2026) (Shift 3)
The correct answer is

The fuse will blow even during normal load conditions.

A fuse is a protective device whose thin element melts and breaks the circuit when the current through it exceeds its rated value for a sufficient time; the rating is chosen a little above the normal load current.

Here the circuit normally operates at 28 A, and the original fuse was correctly rated at 32 A, comfortably above the running current so it does not blow in normal use.

Replacing it with a 16 A fuse sets the trip level well below the 28 A working current, so the element carries almost twice its rating during ordinary operation.

At 28 A through a 16 A element the fuse wire overheats and melts, so the fuse blows even under normal load conditions, causing nuisance tripping and loss of supply.

It certainly cannot let the equipment run at higher current safely; a lower rating means less current capacity, not more.

It does not give improved overload protection without drawback, because a fuse that opens during normal running is unusable, and the voltage rating (unchanged at 250 V) has nothing to do with the melting, so no insulation breakdown occurs.

Hence, the answer is The fuse will blow even during normal load conditions.

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