A wire made to fail
Too much current can melt the plastic in a plug. Home circuits have a safety part for this.
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Step 1 of 3
- The loop is closed. Everything is cool.
- Too much current. The fuse warms up.
- The fuse melts. The loop is open.
The rule
A fuse is a thin wire that melts easily. It sits in the circuit. Its size is chosen to suit the circuit's normal current.
Too much current makes every part warm. A fuse of the right size melts first. The fuse is thin, and a thin wire warms more. The loop opens, and the current stops.
Watch out!
A thicker fuse is not safer. It may never melt. Then another part gets damaged.