Fuse
A fuse is a protective device in which the conductive element inside melts under overcurrent and opens the circuit permanently. Its basic job is not to save the device but to protect the cable before it heats up enough to turn into a fire. That is why its rating is chosen below the cable ampacity and above the load's continuous current.
The fuse element heats in proportion to the square of the current; once a certain energy has accumulated it melts. This behaviour is defined by the time-current curve: it can withstand slightly above its nominal rating for minutes, while at several times that current it opens within milliseconds.
- Fast and delayed types: motors and coil loads draw a high inrush current at start; the delayed type tolerates this transient peak, the fast type blows.
- Location: the protection is always at the supply end of the cable to be protected.
- Single use: a blown fuse is replaced, not bridged or wrapped with wire.
In vehicle-mounted installations of AXI remote controls and drivers, a fuse is always fitted in the supply line. If the fuse blows, increasing its rating is not the solution; an oversized fuse does not protect the cable and the source of the fault, a short circuit, a welded contact or an overload, stays where it is. Find the cause first.
Context in which this term is used: Installation, redundancy and field continuity