Fuse wires. Three different strengths of fuse wire wrapped around a cardboard holder. The different strengths are for use in different types of electrical circuit in the home. The strength of the wire depends upon it thickness. The weakest, and thinnest, is the five ampere (amp) fuse, with the thirty amp fuse being the strongest, and thickest. Fuse wire is a safety feature used to protect electrical circuits from excessive currents. At a specific current the fuse wire melts, or 'blows', breaking the circuit.