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Thread: Negative Earth V Positive Earth

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    Negative Earth V Positive Earth

    This will probably open a can of worms.
    We had a very experienced (older) maintenance bloke come over to the Island to fix our generator and he commented on how much rust was evident on the outside. It sits out in the weather and considering lack of proper maintenance it receives, the 23,000 + hours running time is amazing.
    He also commented that the old American cars that were positively earthed did not rust as much as negatively earthed vehicles from the rest of the world. How is this so? There must be a scientific answer for steel and electricity to make rust. I wish I studied chemistry at high school instead of just attending class.
    If this is true, I can understand why they changed to negative earth because if a car did not rust away, they would not sell more new cars
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    Interesting considering cathodes and anodes used on ships hulls for corrosion prevention, normally the anode (positive charge) would erode instead of the cathode (hull), so if anything positive earth or in vehicles case positive ground points would likely encourage corrosion in the copper wire, same principle as cathodic protection..anyhow, too many beers and dead brain cells ago to debate so have a read here

    https://mgaguru.com/mgtech/electric/et098.htm

    and draw your own conclusions.
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    Selfishly, this is a cool thread to read/learn hopefully answering my questions too Legends
    Some 25+ years ago I was given a task from the boss then (hard yakka Irish mentor :-)
    Ran his DitchWitch dead straight under contract required along the Maribyrnong City River perpendicular to Melbourne’s west gate bridge.
    Sucks when we don’t get to fully backfill and complete a job but was slip/told it was an anodey/cathodey thingy going in to protect some serious infrastructure underground & above


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    Telephone exchanges used 50v with positive earth to avoid problems with electrolysis. The positive earth system means that the ground side of things is the side that gets depleted (the anode) which matters when dealing with things like the very fine wire of the relays and electromagnets etc which were the basis of the old telephone 'step-by-step' technology. This started with the poms who probably had a much bigger problem with moisture (based on their climate) which is a key ingredient for electrolysis - if it is kept dry then there is little issue either way.

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    Are land rovers still positively earthed?
    2008 CRD Wagon, 193,000kms and counting....

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    No expert at all but the major oil pipelines I've been on all have 'cathodic' protection sites situated regularly along the main lines. I was told this was to help prevent corrosion of the pipeline.

    Not my field of expertise though. Where's @Cuppa?
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    Quote Originally Posted by FNQGU View Post
    No expert at all but the major oil pipelines I've been on all have 'cathodic' protection sites situated regularly along the main lines. I was told this was to help prevent corrosion of the pipeline.

    Not my field of expertise though. Where's @Cuppa?
    A little birdie tells me you know exactly where I am! Hope you had an enjoyable time out west. I actually went looking on the ‘net for the answer to this question about why cars changed to negative earth. In a nutshell I could find no agreement, only several different reasons repeated many times.
    The cathodic protection thing which I reckon is a bit suss, something to do with a change to alternators with internal diode control which sounded possible even though I didn’t fully understand it, ��, and also suggestions that it was somehow cheaper for the manufacturers... which I also didn’t quite get. Another possibility was the introduction of radios into cars - perhaps anyone who knows a thing or two about radios might comment?
    Last edited by Cuppa; 26th February 2021 at 09:01 AM.

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    Once upon a time, cars, tractors, busses etc were either pos or neg earth depending on the manuf IIRC some old school Ford were neg but a lot of other yank stuff was pos and either was OK back in those days.

    Pos earth grounding as a "norm" came from the early days of telegraphy where the vitals were Copper and Copper alloy (which is more noble than iron) so that meant the copper components were galvanically protected in a pos earth scenario so they didn't corrode as much and lasted much much longer.

    Once silicon semi-conductor technology became viable it meant a lot of the electronic components had the -ve or cathode common to the case.
    Because the case was also the heatsink it meant you would have to electrically insulate the case from ground in a +pos earth so that meant the heatsink was less effective and shorts more likely.
    This meant it was much easier and cheaper for manuf to produce -neg earth vehicles.

    Executive summary is that solid state semi-conductors were pretty much responsible the death of +pos earth circuits in vehicles.
    Last edited by the evil twin; 27th February 2021 at 06:21 PM.
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