What should I do if the fuse keeps blowing?
A fuse is a symptom, not a cause. First distinguish how it blows: blowing instantly means a short circuit, blowing after running for a while means overload or heating, blowing only at start means an inrush current problem. Disconnect the device and test the line on its own, measure the voltage drop under load and treat every connection above 0.5 V as faulty. Enlarging the fuse is not a solution.
Start the diagnosis from the timing of the blow:
- Blows as soon as it is fitted: there is a short circuit. Disconnect the device from the line. If the fuse still blows, the fault is in the cable; look for a point that is chafing on sheet metal, crushed or pinched. If it does not blow, the fault is on the device side.
- Blows after a while: the current is close to the limit. Measure the real current with a clamp meter. If the device is drawing more than normal, the mechanical load may have increased; if the current is normal, the fuse or holder may be heating up and fatigued.
- Blows only at start: the inrush current does not suit the fuse type.
Then make a physical check. Inspect the fuse holder terminals and cable lugs visually; a blackened, overheated or corroded terminal is both a source of resistance and a source of heat. The drop measured across the holder under load should be below 0.2 V; if it exceeds 0.5 V the holder must be replaced.
What not to do:
- Fitting a fuse one step larger: it leaves the cable unprotected.
- Bridging the fuse or wrapping it with wire: this is a fire risk.
- Replacing the device without finding the cause: a cable fault will hit the new device too.
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