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An Answer For Negative Grounding Of Vehicles

12-16-2010, 10:27 PM
There has been a lot of discussion on negative vs. positive grounding of vehicles here including a thread I started a while back.
The reason given for negative grounding was to standardize grounding in vehicles.

Today I came across this article with this bit of information about WHY they chose negative vs. positive grounding:

Why Are Vehicles Negatively Grounded? The best explanation to this question comes from a 1978 Rolls-Royce Enthusiasts' Club service manual.
" has been found that cars wired positive earth [ground] tend to suffer from chassis and body corrosion more readily than those wired negative earth. The reason is perfectly simple, since metallic corrosion is an electrolytic process where the anode or positive electrode corrodes sacrificially to the cathode. The phenomenon is made use of in the "Cathodic Protection" of steel-hulled ships and underground pipelines where a less 'noble' or more electro-negative metal such as magnesium or aluminum is allowed to corrode sacrificially to the steel thus inhibiting its corrosion."...

So the reason they chose negative grounding was to lessen corrosion on the body of the vehicle.
Any comments and confirmation appreciated. I found this very interesting.

12-17-2010, 08:22 AM
Yikes, every car/truck here in upstate NY is rusted badly after 10 years. My 55 Chrysler is not, as a 6v pos. gd car. But it has not been in the sno/rain for 25 years. LOL Sounds good in theory, but I think there is more to this I am sure a thorough Google search would reveal more info.

12-18-2010, 01:23 AM
Hi Max!

As you pointed out, other New Yorkers keep their cars out in the elements and your 55 Chrysler is kept protected in the garage.
All things need to be equal for a fair comparison.

I did a little more research and came up with this from an Australian Rolls Royce club site:The RR Service Sheets dated 1960 detail the problems of radiators being choked by silt (mostly iron oxide from the block) being deposited by electrolytic action. A system of braided bonding straps was developed from the generator to the radiator to try and reduce this problem and finally the generator was electrically insulated. The cause of these problems was, of course, the positive frame so that is why the company changed polarity to negative frame.

I am trying to find a link to the RR service sheets, but haven't found them yet.
It seems to me there is some truth to this no matter how minor the effect might be.

Even if positive polarity didn't cause a noticeable increase in corrosion, it appears manufacturers believed it did, and thus impacted their decision to change to negative grounding.

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