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I'm installing a ham radio transceiver into my car, which draws up to 25 amps and can't be used with the 12V socket. Instead, I'm following this and this and similar guides, which recommend running a dedicated pair of 10 AWG wires to the positive battery lead and engine ground point. (They recommend not using a chassis ground because of the RF interference it introduces.)

Most of these ham guides recommend using fuses on both wires in the engine compartment as well as the radio end. However, do I really want the ground wire to be fused? If something bad happens, don't I want an unimpeded path to ground? Is there a failure mode where having a fuse on the ground wire is beneficial?

This question is about ham radios, but I suspect it applies to standard car audio as well.

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I have fitted many accessories to cars, trucks and agricultural vehicles, some taking less than 1 amp and others several hundred or more.

I have never put fuses on the earth or ground side. If the ground side fuse breaks then the device may actually cause more damage to itself or other items as it "finds" an alternate path to ground.

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The basic purpose of fuses is to protect the wiring, not the equipment. The radio itself should be protected internally against anything you can connect it to (within reason).

Electrical wiring can fail either open circuit or closed circuit (e.g. wires chafing on sharp edges may cut through the insulation).

The purpose of a fuse in the negative wiring is to stop multiple failures that develop over time from sending the full battery load through your radio power cable. For example, suppose your negative power cable chafes through and shorts to the vehicle chassis. Quite likely, there will be nothing to tell you that happened. Then one day the car battery connection to the chassis corrodes through, or is disconnected and improperly reconnected - and the circuit meant to supply a few hundred amps to the starter motor now goes through your radio negative power lead. Again, you might not even notice (though cranking and starting might be a bit more sluggish than they used to be) - until eventually the insulation degrades through repeated overheating, and your next attempt to start the car puts a dead short across the battery, which causes a rather impressive explosion...

Most likely, none of the above would ever happen to your particular vehicle even if there was no fuse. But that's why the fuse is there - as the UK lottery advertising slogan says, "it could be you".

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