Positive/negative ground

[Dave Sherman]

What was the real reason for switching from positive to negative ground? I've heard two theories: Fighting corrosion and supposedly improving how spark plugs fire, since the spark could more easily jump from the hotter outer electrode to the cooler center electrode. The latter doesn't make as much sense to me, since the polarity would be determined more by the polarity of the ignition coil's secondary winding.

Just pondering since my MG came from the factory with a negative ground system, but apparently the remnants of positive ground are still there; the negative battery cable is red and the positive cable is black.

 

[John_K]

Originally Posted By: Dave Sherman
What was the real reason for switching from positive to negative ground? I've heard two theories: Fighting corrosion and supposedly improving how spark plugs fire, since the spark could more easily jump from the hotter outer electrode to the cooler center electrode. The latter doesn't make as much sense to me, since the polarity would be determined more by the polarity of the ignition coil's secondary winding.

Just pondering since my MG came from the factory with a negative ground system, but apparently the remnants of positive ground are still there; the negative battery cable is red and the positive cable is black.


Wikipedia says "In modern automobiles, the grounding is provided by connecting the body of the car to the negative electrode of the battery, a system called 'negative ground'. In the past some cars had 'positive ground'. Such vehicles were found to suffer worse body corrosion and, sometimes, blocked radiators due to deposition of metal sludge."

John

 

[Trav]

Having owned a few Pos earth vehicles i can say the rust wasn't any more or less then neg earth systems.
This debate raged for decades and from what i read it was just a standardization thing nothing more. Electrically it was claimed there is no difference in function at all.

 

[ARCOgraphite]

Tires are semi-conductors to bleed off static buildup, and they are attached to the frame.

 

[mechtech2]

Negative ground was generally instituted because of the spark plugs.
Not for better firing -that would be the same.
But because of wear of the thin and much hotter side electrode.

With modern precious metal tipped plugs, many plugs now DO fire the 'wrong' way. This is common is waste spark ignitions [2 plugs firing at once].

For the rest of the car, it makes no difference.

 

[morris]

back in the dark ages i read a article about his subject.. all i can remember is that general motors did a LOT of research on this subject. generally 6 volt systems had positive ground, but one car had a 6 volt positive ground, a 1954 imperial

 

[OVERKILL]

I've never noticed a difference. We had a number of positive ground boats. And a number of negative ground ones too. Never noticed a difference in the plugs between the two either.

 

[NateDN10]

Originally Posted By: ARCOgraphite
Tires are semi-conductors to bleed off static buildup, and they are attached to the frame.

What does this have to do with the topic?

Also, tires are not semiconductors. Semiconductors can act either as conductors or insulators, depending on the conditions (for example, voltage applied to a transistor gate).

 

[SS1970chrysler]

My 48 Packard and 41 Studebaker were positive Ground. Standardization was inevitable as the larger auto companies were Negative ground already. When the switch was made from 6 to 12 volts, all companies went to negative ground.

 

[Trav]

Quote:
When the switch was made from 6 to 12 volts, all companies went to negative ground.


Some Euro cars were imported to the U.S. in the 60's with 12v pos ground. Ford Cortina's, Jag, MG come to mind.
Many English cars used 12v pos ground up to 1968 or thereabouts even on the exports.

 

[Silk]

British cars were nearly all 12v after WWII,Ford being one of the only 6v systems...and all were positive earth.Negative earth came with alternators in the late '60's,although there were a lot of negative earth generators too.

 

[ARCOgraphite]

Originally Posted By: NateDN10
Originally Posted By: ARCOgraphite
Tires are semi-conductors to bleed off static buildup, and they are attached to the frame.

What does this have to do with the topic?

Also, tires are not semiconductors. Semiconductors can act either as conductors or insulators, depending on the conditions (for example, voltage applied to a transistor gate).
OK, High Impedance resistor. You want the frame at ++ and the tires at GND potential? No.

 

[vintageant]

1925 Alvis - positive earth
1937 Alvis - negative earth

Both 12 volt - go figure!

 

[mechtech2]

Alvis has always been at the cutting edge of technology!

 

[roadrunner1]

I'm not discounting any of the above explanations, but I was always told the reason for positive ground was that was the natural flow of electricty. At least in the marine environment positive ground was thought to be much easier on steel hulls regarding hull corrosion. I was never much of a believer of this, we have one boat until twelve years ago was positive ground.

I still have several engines that are positive ground, its really not a big deal as long as you know what you are dealing with

 

[Samilcar]

No good reason for picking positive or negative to use as a ground, other than standardization. Found this handy illustration of electrical flow:

http://mste.illinois.edu/murphy/HoleFlow/HoleFlow.html

"You can think about current as the flow of electrons, which go from negative to positive, or as the flow of holes, which go the other way. If you are really into semi-conductor theory it makes a difference which one you use, but otherwise you aren't likely to care. We usually use hole flow because the direction agrees with the decision that the early scientists made when they had to pick a direction to use in their calculations. It's traditional."