DODGY FUSES

[malc_edward]

Be warned of cheap blade fuses .

a friend of mine asked me to look at his fuse box after changing a blown fuse it appeared that the replacement fuse had melted but not blown connections in the base of the fuse box were clean and tight but still no operation of the water pump the fault turned out to be shorted turns in the armature of the waterpump. but why did the fuse not blow? well a little more testing on the faulty pump in its faulty condition the pump was drawing 21.6 amps @12 volt dc. The fuse was rated at 10 amp and was quite happly drawing over twice its rated current and not failing instead just getting hotter and melting the plastic.

Fuses can have more current drawn through them than they are rated at (for a while) before blowing to compensate for surge currents on startup of equipment.

but this fuse has had this overload for more than 25 mins in fact it took 38.4 amps before blowing not bad for 10 amp fuse.

Other fuses out of the pack were tested with similar results they were brought from a local market.

The only fuses i use are "little fuse" as used by many car makers a trip round the local scrap yard can produce loads of these fuses for only a few pounds.

The faulty pump was reconnected with a 10 amp little fuse connected and blew stright away so word of warning cheak your fuses you may have a potential problem installed if using cheap fuses.

[Brian Kirby]

Malc

It might be worth checking the pump wiring, which is what the fuse is supposed to be protecting.  With that much overload, I'd think it may have been getting quite hot as well.  Also, 10A seems quite a high rating for a water pump.  Was this the correct original fuse rating?

[malc_edward]

the pump wiring is fine it is wired in 2.5mm and only had been intermittley used when the pump was faulty the tests for blowing the fuse and current comsumption under fault conditions were carred out on the benchthe current taken by the new pump is 6.8 amps so the 10amp fuse fitted is ok for the job