Fuse Sizing
Determining the fuse rating that will protect the supply line. The general rule is to take roughly 125% of the continuous load and then round up to the next standard value. For the AXI LFT20 the manufacturer declares an average current of 10 A; from this value 12.5 A is calculated and a 15 A fuse is recommended in practice.
A fuse protects the cable, not the load. That is why the selection is made between two limits: it must be above the normal operating current so that it does not blow needlessly, and below the current the cable can carry so that in a short circuit the circuit is broken before the cable heats up.
- Calculation: start with continuous current × 1.25 and round the result up to the next standard value (7.5 / 10 / 15 / 20 A).
- Inrush current: DC motors draw several times the continuous current at the first instant. This brief peak must not cause the fuse to blow immediately; a time-delay type fuse suits this behaviour better.
- Location: the fuse is placed as close as possible to the battery post; the section in between is left unprotected.
A frequent mistake is to fit a fuse of a higher rating in place of one that has blown. This does not fix the fault; it only disables the protection and puts the cable at risk. Repeated blowing always has a cause: mechanical binding, a short circuit or a wrongly chosen rating.
The context where this term is used: Converting a tractor hydraulic lever to electronic control