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Avoiding Electrical Grounding through Chassis? Corrosion Avoidance.


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Morning All,

In a forum post I read recently (may not have been this forum - I can't find it!) the original poster discussed their work towards re-wiring a project vehicle. They'd decided to use dedicated earth leads rather than using the chassis and other posters complimented this citing reduced corrosion as a good reason for doing this.

Are some of the early Land Rovers positive earth or is there a general concern that using the chassis and bodywork as a ground in a negative earth system can exacerbate corrosion issues?

My understanding of it is that on each connection (ie ground strap bolted to the chassis or body from engine) with the addition of humidity or water the more positive side of the connection will corrode in favour of the negative. So in general the wiring loom connections corrode rather than the chassis or body. The only point where I can see this going slightly bad is the final strap from the body/chassis back to the negative post on the battery. In this case logic would sugest doing all you can do to reduce any contact resistance by making the connection as good as possible and sealing it as far as possible.

I'm initially resistant to using dedicated earth cabling back to the battery as this would need to be a significant CSA to match the equivilent condustion through the chassis and therefore expensive. In addition it adds more potential points of failure for the loom and if the resisitance on the return isn't considered carefully it would cause an additional voltage drop considerarion for items far from the battery like rear tail and work lights.

All that said I have considered dedicated earth runs back to the battery for items like radio and any other electronics to try and help reduce electrical noise issues.

Cheers.

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Hmm...

We use dedicated earth cables throughout the vehicle and use the chassis.

Positive earth is said to have less corrosion issues but grown ups will know more.

Anything in contact with air will corrode so I just live with it.

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I thought negative earth had better corrosion resistance due to the electrolitic reactions corrowing the wiring rather than the chassis? Have you got any links on the positive earth being better for corrosion resistance?

...seen a few mentions about corosion around where wires went though bulkheads with poor insulators causing corrosion on the bulkhead. I'll add links to this later and others as I find them.

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Ahh ok.

Found this on electrolysis:

So in this example the rust is removed from the negative part of the the cell. This process also removes the paint, which would leave the newly clean metal surface open to atmospheric corrosion.

So voltage applied and the posative side is sacrafised and the negative cleaned. Voltage off and the newly cleaned metal is vunerable and rusts.

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The thing to remember is that wherever there is a steel-aluminium joint that can get wet it will corrode and break down the ali due to the electrolosis. By making as many of the earth connections direct to the battery with some kind of earth ring/busbar, you'll reduce the corrosion. Just making sure the connections are as good as they can be won't really help the situation as far as I can see. Should also point out that it is a good thing to keep the body earthed, but earth all the other stuff separately back to the battery.

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I don't see any gain in not using the chassis as earth, maybe it works if you isolate everything, but that is almost impossible for things like an alternator or starter motor. If you look at a door, it doesn't carry any electric connection, but they corrode badly. The only thing that works is going back in time and have positive earth; cars that used to have positive earth did not suffer from galvanic corrosion. Have a think about that for a moment!

Daan

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Dedicated grounds will certainly help with having the correct voltages at the destinations, after all copper is a much better conductor than steel. But you cant avoid some of the current going through the chassis, unless you go to great lengths to isolate it. Its a very complex circuit with lots of parallel paths.

I would say its possible in a ground up build, but difficult to achieve in modification.

Having said that adding grounds can't do any harm, some good, and MAY mitigate corrosion to an unknown degree.

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You can run separate earths for everything, I did on the 109, on the grounds that a single length of copper wire back to the battery is a better path for electrons than a loose assemblage of steel & aluminium with a load of joints, paint, movement, and the odd bit of corrosion in the way. Easier to trouble-shoot too.

Doesn't take much on a standard landy really; one decent wire to each corner for the lights, an earth point for the dash loom (which may as well be on a stud on the bulkhead) and the engine & box need an earth strap whatever you do, mine is a length of 35mm copper from a starter bolt back to the battery -ve.

Freelanders have some nice 6-way earth-stud / spade terminals scattered round the engine bay, I ripped about 5 out from a scrapper for a couple of quid, makes multiple earths very neat.

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