Another wiring question

Thanks guys, its sounds as though I should be OK, the wires are 6mm and very short. I was just worried that it might act like a weak link in a chain, with all the good work of the thick cable being undone by the thin. I never did understand electricity! All I know is that you can't see it coming and it bites.

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Think of it as a fusible link :-)

Fusible link? Sounds familiar, I think I've got one of those. Thats the thing that fooled me for a while because it was a loop of wire with a fuse holder in the loop. Took me a while to figure out that I had to cut the wire! My daughter was eying it up as a bracelet.

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Using the body for earth is not a good idea - the earth should ideally be returned to the feeding battery with the same thickness cable as the active.

Thanks Phil,

The main cable is dual core, on the advice of the shop the sockets earth back to the battery negative, though I realise that this isn't strictly necessary. The battery earth is a 25mm cable to , um, can't remember without going out to the car park exactly where I earthed it! (I'm sure that it was somewhere good!)

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Gerhardp1 - Why?? Or is this another electrical myth :-))

Phil,

In my opinion, there are too many chances for a high resistance connection through a vehicle body to use it for a reliable earth. I don't see that it can ever be as reliable as a wire back to the battery. I believe that's why there's always an earth strap from battery to starter/block as well as to the chassis.

It doesn't mean earthing through the body won't work.

Cheers.

Hi Gerhard,
I agree with everything you've said. But the vehicle manufacturers earth almost everything to the body, but do it well. Too many dodgy installations have poor earth. But if you take every earth back to the battery, you can have a stack of extra wiring, so I think you have to draw a line somewhere.

IMO, the high amp draw stuff like Winch, compressor, driving lights and HF radio get their own earth wire back to the battery. But everything else I have (radio, fridge, fluoros, camera, computer) uses low amps, so I earth everything else to a good earth on the body. Fridges and fluoros don't use much power these days.

As well as removing paint for a good earth, I tap the hole, and smear the metal with vaseline to stop corrosion.

Cheers

When I was wiring up my stereo amplifier I which _Affordable_Storage_Drawers.aspx 60amps max, I was told to run a earth wire back to the battery, I asked why and he said to avoid possible audio interference, nothing about the body not being able to handle that much current. I just earthed it to the body and it is fine (no humming etc).

Many good drinking hours are been spent chasing faulty earths.

As most long term trailer owners have seen, bad earths lead to trailer lights coming on when they aren't supposed to, eg put the foot on the brake and the clearance lamp comes on as well. Caused by bad earth, and the brake light finds any path back to earth it can.

Similar occurences happen within vehicle wiring (mostly in add on work, not original stuff) and sometimes an earth wire sized to supply one device ends up carrying the earth return current for other devices as well. Not always noticed until the smoke gets out! And, as most of us know, everything runs on smoke. Once the smoke gets out, it stops.

So I commend Phil G's advice on seperate earth wires for all your big items back to the battery.

Me, i do it for just about everything i do. If i am under the car running 1 wire, i can run 2 in about the same time. In fact, for most items you buy 2 core cable and it takes about the same time as running 1 single core.

Crowding at the negatve terminal can be a problem, but you have to do something about that for the positve as well, so i can cope with it on the negative side.

Earth and Neutral bars used in doemstic house wiring, available from electrical wholesalers, provide and easy solution.

Radio intereference on some items is an issue. My Engel owners manual tells me to run the negative back with the positive for this reason. I trust them to build the fridge better than i can. Why wouldn't i trust their advice on the wiring? The fridge cost $1000.00. How much does it cost to just run the neagtive the way they say? Can't be stuffed worrying about it. Nike.

To Jimbo's post, i'd like to add 1 word. Yet.

Trevor

I see your point. If the earth to amplifier was to fail due to being run through the body then the return path to the battery would be through the RCA signal leads and trough the head unit. This alternative path would have no chance of coping with the current from the amplifier. Prehaps I should use the RCA's with the earth cut off and not connected at one end

Why not just run the earth back to the battery?

Run the earth back to the battery as Gerhardp1 says, in the same gauge wire as the active, some say also to fuse the earth cable too, although I am not a fan of that.