will solidify into an amalgam of glass and
partly fused sand, known as fulgurite, which has excellent insulating properties. The
sudden rapid rise in circuit impedance results in the fault current being driven down
towards zero well within the first loop of fault current. This sudden collapse of fault
current flowing through the inductance in the circuit will produce a voltage spike.
Fuse standards require that the fuse is designed to limit this voltage to a maximum
specified value, which for a 12 kV fuse is 38 kV peak