Ok so i'm hoping that someone can explain to me in basic terms: in an un-fused circuit what could actually cause an electrical component to be damaged by current flow. I'll explain the reason for my question.

I have recently fitted custom dash gauges to my Jeep. The instructions recommend fitting a fuse to avoid damaging the gauges, so that is what i have done. What i am trying to get my head around is how the gauges could actually become damaged if there was no fuse. Power is flowing through the gauges which are providing a resistance and then the power is flowing back to the battery. So what could cause the fuse to blow? I guess some kind of short circuit but i'm struggling to get my head around where the short circuit would occur that could damage the gauges (if i had no fuse). Maybe i'm over simplifying the system in my head but the way i am thinking of it is: if i had a simple bulb in a circuit, if that circuit shorted out then the wire would be destroyed but the bulb would still be ok? wouldn't it? because the short would bypass the bulb.

So in the case of my gauges what could hypothetically fail that would cause my gauges to be damaged by excess current flow? Or are the instructions wrong and what they actually mean is 'a fuse should be used in case something in the gauges fail in order to prevent a potential fire' and not 'a fuse should be used to protect the gauges'?


1 Answer 1


I think you are virtually "there" with your reasoning.

Fuses are invariably used to protect infrastructure i.e. wiring from catching fire. In a motor car that prospect must be paramount and the fuse will stop a hundred or so amps flowing through "lightweight" cable should your new gauge develop a fault.

It's no different to your home - fuses are there to protect infrastructure and not your wife's hair-dryer.

  • \$\begingroup\$ Ah ok i think i get it, so the fuse is to protect the wires from a fault with the gauge/hair dryer etc and not to protect the gauge/hair dryer from a fault with the wire. The component has its own resistance that prevents too much current flow damaging it and the fuse is just to protect the circuit from overheating should a component fail or a short circuit occur. So a short circuit cannot directly cause damage to a component only to the un-fused circuit. \$\endgroup\$
    – m.m
    May 29, 2018 at 10:35
  • \$\begingroup\$ Correct @m.m !!! \$\endgroup\$
    – Andy aka
    May 29, 2018 at 10:46
  • \$\begingroup\$ I think that depends on the type of gauge. If it's an ammeter for example, the gauge has a low (ideally zero) resistance. In that case the fuse very well may protect the gauge, as well as prevent a fire. \$\endgroup\$
    – Phil Frost
    May 29, 2018 at 10:58
  • \$\begingroup\$ @PhilFrost very true. \$\endgroup\$
    – Andy aka
    May 29, 2018 at 13:09

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