Fuses
The simplest protection: a wire that melts when current exceeds its rating for long enough.
Easy
A fuse element melts under overcurrent and the arc is quenched (often by sand in HRC fuses). Key ratings: rated current, breaking capacity and time–current characteristic (fast-acting vs time-delay/slow-blow for motors and transformers with inrush).
The let-through energy is the value — HRC (high rupturing capacity) fuses limit fault current very quickly. Fuses are cheap and fast but must be replaced after operating; always replace a blown fuse with the same rating and type — never with wire.
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