Fuse wire is an uninsulated conductor, usually made of tinned copper or a lead-tin alloy, rated to melt at a specific current. It is manually wound between terminal screws in traditional porcelain fuse carriers. While largely superseded by enclosed cartridge fuses and circuit breakers, it is still found in legacy industrial installations and older distribution boards.
Heard on the job
The lighting circuit went dark again, so grab the card of 5 amp fuse wire and rewire the carrier.
Insider tip
Replacing a blown fuse wire with a thicker gauge or a random piece of copper wire is a classic, highly dangerous error that destroys the circuit's protection.