Fuse on earth wire for Engel

I said I picked up a plug, when in fact it was a socket.
Dave

There is absolutely no need for the fuse on the negative wire. If the negative wire somehow touches the body of the car nothing can happen as it is already connected to the body via the battery. However, if the positive wire should somehow touch the body the fuse is there to blow and avoid a short circuit and possibly a fire. The fuse must be as close to the battery as possible so as to protect all the positive wire from trouble.
I hope all that makes sense.

Hello Dave,
The fuse in both legs of an extra low voltage automotive device such as a fridge is a good idea.
Under certain rare faults in your vehicle wiring the fridge or other device could be asked to carry the full starting current of the vehicle. (Also dependant on the way it's wired)

So without sitting down over a beer and some obscure electrical drawings and cat scratchings, it's all good.

Geoff.

Dave,

I may be easier to understand if you don't refer to the negative wire as an earth wire but a return wire. The socket circuit may, or may not, use the vehicle body or chassis as a return path to the negative terminal of the battery. This will depend whether the circuit for the socket uses two wires (black & red) and whether they run all the way to the battery terminals. It cannot be compared to an earth wire when related to domestic 240 volt AC electricity, which provides an alternative safety circuit to "ground". (With domestic 240 volt AC, the neutral link is grounded, (earthed) at the switch board end)

It certainly won't do any harm to leave it as is and will give added protection to your fridge in an abnormal situation.

Fusing of the Earth lead is of an appliance is only helpful IF -

1. The device's earth lead runs directly back to the battery (not to the body)

2. The device has another earth connection to the bodywork e.g. via a radio aerial cable.

Then IF the Battery-to-body cable fails, starter current will flow from engine to body to radio to battery.

If you have a metal cased fridge and the case is in contact with the cars bodywork, you would also have this fault-current path.

The classic example of this type of earth or return fault that you see frequently are trailer lights. Ever see the brakes lights flash with the indicators or indicator lights light up when the brakes are applied?

This is because the 12V is finding it's own way back to the battery by the lowest resistance path. It doesn't care how much you paid for the device that offers the lowest resistance to the battery, so if your $3.5K HF radio or $1.5K fridge is it then that is what it will use. Fusing the negative of the fridge etc provides some protection against this.

Worst case, as explained above, is if the starter motor deceides to push its very high current through something. Then there will be smoke followed by tears.