Reason for Neg vs Pos ground?

[TJ Hopland]

Was there a reason that for most of the early days of electrical systems Pos ground seemed to be the most common?

Any idea why the change?   

Was the change usually at the same time as the change to 12v?

Was this all the same around the world?

[Otto Skorzeny]

Great Britain retained "positive earth" as they say, at least into the 60s. I think everybody's negative ground today.

The switch to negative ground and 6v to 12v didn't always occur simultaneously with a particular make. Different makes switched at different times. Cadillac went + to - in 1946 but went to 12v in 1953.

Ford switched to 12v in 1956.

[Doug Houston #2257]

I've covered this several times in the past, so I'll try to be a bit laconic here. The issue was distributor point erosion. It was thought that it was less with pos. ground, but it never seemed to make enough difference to sniff at.

Chrysler had a 12 Volt system in a couple of fifties era cars,and I think that they had positive ground. I'd need to check on it.

Chevrolet had a reversing switch on the distributor points, that reversed them each time the starter pedal was depressed. It was on my "41 Chevy as original equipment, but it was removed before I got the car. I have a new switch kit for it somewhere, but I doubt if I'llever install it. Everything's fine as is, so I'm going to let it be.

[Otto Skorzeny]

So why the universal switch from positive to negative ground?

 As far as i know, it doesn't matter to electricity. As long as a circuit can be completed, everything works.

Why didn't everybody just stay with positive ground and use 12v?

[MOTORNUT]

So why the universal switch from positive to negative ground?

 
Why didn't everybody just stay with positive ground and use 12v?

Negative ground is universal now because modern electronics use negative ground.

[Otto Skorzeny]

Yes, we know that, but it still doesn't answer the question.

Modern electronics could easily be positive ground. Why, since positive ground was nearly universal for the first 50 years of automobile electrical systems, did the industry decide to convert to negative ground systems?

What is the reasoning behind the switch?

[JKF]

Wouldn't surprise me if it has to do with patents. A handful of big manufacturers after WW1.
If I remember correctly from school the flow of current is from neg to pos. Lucas had something going once.

Bought an Austin Mini MkI 4spd Automatic 15 yrs ago that the seller never managed to fix the electrical system in. I Drove it all summer but had to recharge the battery several times. Finally I took the car to an older gentleman specialized in brittish cars. He looked under the hood, firmly shifted the battery cables to positive ground and told me to drive away. Far away.
Perhaps there are no fools anymore so "fool proof" positive ground isn't needed

J Kjerrulf

[Ted in Olympia WA]

I may be wrong but I bet it has to do with sourcing out the making of components like heater motors and starters.  To be more efficient it's better for everyone to be the same and cut costs.

I heard the main reason for going to 12 volts was to cut down on the amount of wire needed in the car.  I guess a 12 volt system needs a wire half the size to carry the same amps?  This saved on the copper needed and reduced cost.

TED

[Otto Skorzeny]

Ted, your talking about 6v to 12v. The reason for that switch is obvious.

We want to know why negative ground is now universal whereas for the first half of the existence of the automobile, positive ground was universal (for all practical purposes).

The accessories can be and were built to whatever specs the car maker demands.  Makers of car heaters didn't produce a particular model a certain way then and tell GM to take it or leave it. It was and  is the other way around.

So the question still remains; Why did car makers decide to switch systems?

[Bill Balkie 24172]

Hello Otto, I think it all has to with corrosion of wires .The answer is simple enough..using negative battery reduces corrosion in the thousands of splice connections of the cables. The same technique is used in bridges and dams. A small negative (dc) current is passed through the steelwork and reduces electrolisys damage, or reverse electroplating the earth.  I am not an engineer but i found this out on the internet

Ted, your talking about 6v to 12v. The reason for that switch is obvious.

We want to know why negative ground is now universal whereas for the first half of the existence of the automobile, positive ground was universal (for all practical purposes).

The accessories can be and were built to whatever specs the car maker demands.  Makers of car heaters didn't produce a particular model a certain way then and tell GM to take it or leave it. It was and  is the other way around.

So the question still remains; Why did car makers decide to switch systems?

[warren rauch]

  In some of the earliest Service Man issues they sometimes answered questions like this.
  Date Jan1,1928 Q ; Why is the positive terminal of the battery grounded on Cadillac and LaSalle cars?
                         A: The positve terminal of the battery has always been grounded on Cadillac elcetricial systems. The advantage is that with this arrangement the positvie terminal of the battery is more easily replaced if it corrodes, and our expreience has shown that the positve terminal usually corrodes first.
    Believe it or not. Warren

[The Tassie Devil(le) (Bruce Reynolds)]

Oh, those were the days when things could be replaced, repaired, or just plain fixed without spending huge amounts of hard-earned cash.

Bruce.

[Otto Skorzeny]

Interersting Warren.

If that were really the case, though, why did Cadillac switch in '46? Certainly the laws of physics didn't change.

Probably just a BS answer because the guy was wondering the same thing we are today and no logical answer seems to be forthcoming. The mystery continues.

[Whit Otis, 1188]

It seems that somewhere back in the dark ages, I read that positive ground was not universal back in the old days.... in fact that GM themselves did not universally use positive ground.... Cadillac was postive ground, but others such as Olds were not..... but, I don't remember the source on this.... also, the point that Doug Houston brought up was also reinforced as to why some makers used positive ground..... at this stage, I'm not willing to research it.... but it is an interesting topic nonetheless
Whit

[Glen]

I don’t think there was an overwhelming reason for the change to negative ground.  More than likely the need to standardize was the reason for some manufactures to change, but who would change was possibly determined by numbers.  There were more manufactures of negative ground cars than positive ground.  Or the manufactures of the negative ground cars were not willing to change so the rest had to make the change.

It’s also possible there were urban legends that influenced the change.  Such as “Lighting strikes more positive ground cars then negative ground cars”. 

The change was probably not based on science but convenience and politics.   

Glen

[Bryan Thompson]

Good Morning everyone,

After 14 posts I have been surprised no one has mentioned.......
Anyone ever work on the seat of their positive ground car (or other components) and see all the sparks when "grounding" the last connection? This would be very bad for electronic stuff. Not to mention scary.

Just my two cents.
Bryan

[Otto Skorzeny]

But the switch cam before the advent of electronics. Everything was still electro-mechanical in nature.

I imagine the choice probably was somewhat arbitrary but if it was the automakers that made the decision, I would imagine that GM, being the world's largest, carried the most weight.

[Gergely Szentmartony 25603]

It would also help to solve the enigma if we were sure whether Cadillac changed from + to - right after starting tank production (so tanks were all negative grounded) or tanks were all positive grounded and then somebody thought in 1945 that time had come to change to negative.
Unfortunately, I cannot find any information like that in the Service Manual: http://www.modifiedcadillac.org/documents/1940s/1944/1944%20Light%20Tanks%20Service/
I can imagine that military standards allowed only one kind of polarity (let's say the negative) because it reduced the number of further potential technical complications in the battlefields (Chrysler also produced tanks during the WWII). Then, after the WWII everything was ready to use as a negative ground system which did not make any sense to convert it (back) to positive ground.
So, maybe we just think that Cadillac changed to negative ground after the WWII. Maybe the military standards forced Cadillac to change it.
Of course, it is only my speculation which needs to be checked. However, I cannot find any other source than the above mentioned link to a Cadillac tank service manual.

[Otto Skorzeny]

That's a good theory. Now we'll have to find out what the army did with everything.

My guess is that it wasn't standardized but who knows? The military bought all kinds of vehicles "off the shelf" including staff cars (some Cadillacs), trucks,  etc. and they were identical to the civilian versions. I'd suspect that there was a hodge podge of systems. Perhaps the"purpose-built" vehicles met some standard, however.

[Doug Houston #2257]

Normally, after i answer something like this, I never open it up again. This one has gotten to be downright amusing. It will probably go on forever, with never a satisfying answer. There will probably be more theories offered, than cockroaches in Florida.

It rfeminds me of a guy, who once asked why a wheel is used to steer automobiles. Someone answered that the wheel was the most pracatical means of steering the vehicle, so it has been used since time immemorial. He than countered: But there MUST be a better way to do it. He had no ideas himself, but  while he never would admit it, he felt that, after all of those years, SOME improvement must be waiting in the wings. He was solidly convinced that, since time has passed with no chenges, then it was time for SOME change. Someone present suggested that he install a tiller bar on his car. That way, he'd have something different (though inferior), to possibly satisfy his desire for change. People are strange, and there are so many of them!