Why positive ground?

[oj]

What was theory as to having positive ground and what compelled manufactorors to switch to negative ground?
If I recall electrical theory right the voltage flows from positive to negative while current flows from negative to positive.
Any thoughts?

[Jack E/NJ]

Telephone companies originally discovered that copper wiring corroded faster in negative-grounded systems due to electrolysis. So they switched to positive-ground to protect the wires at the expense of whatever metals were connected to the positive ground. This is called cathodic protection (wires connected to the negative battery terminal). So, for an automobile, which would you rather have? Its wiring negative like the phone companies? Or its body negative like the car companies? 8^)

Jack E/NJ

[rotorwrench]

Direction of electron flow was the reasoning behind the positive earth for low voltage systems like all the 6-volt cars were. The 6-volt system is taxed by any resistance in an electrical system. This is why the average wiring is 16 to 10 wire gauge instead of the smaller gauges used in the 12-volt systems. The 6-volt systems needed all the help they could get and flowing electrons directly to the electrical load was as efficient as it got.

In a 12-volt system it's not necessary. Resistance has a much lower effect than with the lower voltages.

[51 MERC-CT]

Not knowing the answer I asked an 8 year old and he replied "because",
and that's good enough for me.

[Mike51Merc]

I had heard, and I'd love to know for sure, that cars were wired with positive ground to help prevent corrosion of the body and chassis. They switched to negative ground because they learned it was better (for the manufacturers) to have the cars rot out so they could sell more cars.

[Jack E/NJ]

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I think it's the other way around. The phone companies wanted to protect the wiring by making them more negative than ground. The car companies wanted to protect their bodies by making them more negative than the wiring.

Jack E/NJ

[Ken Bull]

I always thought it was because Henry Ford was friends with Thomas Edison. Can you imagine there discussions?

[mrtexas]

Originally Posted by rotorwrench

Direction of electron flow was the reasoning behind the positive earth for low voltage systems like all the 6-volt cars were. The 6-volt system is taxed by any resistance in an electrical system. This is why the average wiring is 16 to 10 wire gauge instead of the smaller gauges used in the 12-volt systems. The 6-volt systems needed all the help they could get and flowing electrons directly to the electrical load was as efficient as it got.

In a 12-volt system it's not necessary. Resistance has a much lower effect than with the lower voltages.

What a reason for direction of electric current flow! Modern science has proved that current does not flow from negative to positive as originally thought. Poor old Ben Franklin guessed wrong and we have stuck with him. Doesn't really matter in a practical sense though. We define electric current to be the opposite direction of electron flow. Confused?


http://blog.sciencegeekgirl.com/2009...-current-flow/

“In the past when I taught electricity I always understood that it flows from the negative terminal to the positive. The CPO books and materials have the opposite – from positive to negative. This doesn’t make sense to me in how you generate the flow of electrons, pulling to the opposite charge. Is the book wrong or have I forgotten stuff? 8th grade teacher”

It depends on what you define as “electricity”. Do you mean the flow of “electrons” or the flow of “current”? Because, due to an unfortunate quirk of history, the direction of *current* flow is opposite to the direction of *electron* flow. Take a moment and re-read that, because it’s not what you would expect. If electrons are flowing to the right across this screen, then we say that current is flowing to the left.

[Jack E/NJ]

A current of electrons flows. 8^)

Jack E/NJ

[qmdv]

My old Bug Eye Sprite was 12 volt positive earth. The later cars by the some company went to negative earth.

Tim

[rotorwrench]

There were a lot of misconceptions back in the late 20s that are a lot more clear today. The Model T cars were mostly 6-volt negative ground. When Ford made the change over to the Model A, they were concerned about the way the new ignition system was going work, whether the battery charge would leak through the body to ground, and anodic/cathodic reactions with the body parts. All this stuff was part of the reason that they went to positive ground. Thomas Edison and Henry Ford may have had discussions about the subject since they were close friends but I would be relatively certain that the common consensus of the engineers was to make that change. We have since gained a lot more knowledge in the field that has rendered the worries they had back then to be baseless now.

They were just doing what they thought was best and the least expense at the time. By 1955 they knew that the polarity was not worth worrying about and that modern accessories were going to require 12-volts to get by with minimal warranty concerns and expense.

[42guy]

I had 2 Triumphs and a Jag. All 12 volt and positive ground.

[petehoovie]

Electron flow/current flow....It's all 'theory'.....

[qmdv]

Originally Posted by 42guy

I had 2 Triumphs and a Jag. All 12 volt and positive ground.

NONONO, It is "positive earth" for the Brits

Tim

[George/Maine]

I think when they started using radios with transistors they had to make a standard and went to 12 volt better starting less amps and Neg Ground. They may have never changed if not for that. I have a 54 ford someone changed to 6 volt neg grd and all works good, I don't see any need to change it over to pos grd.

[scooder]

Over here in England we kept positive ground (earth) till about 67-69. Not all companies changed at the same time. But 6 volt was gone way before then, last stuff was Ford with the Popular (Anglia) in 59ish. All the other Fords were 12 volt from 51ish.
Martin.

[Karl]

Originally Posted by scooder

Over here in England we kept positive ground (earth) till about 67-69. Not all companies changed at the same time. But 6 volt was gone way before then, last stuff was Ford with the Popular (Anglia) in 59ish. All the other Fords were 12 volt from 51ish.
Martin.

My Series V Sunbeam Alpine was the first Series of Alpines to go negative earth in 1967-Karl

[JM 35 Sedan]

Originally Posted by oj

What was theory as to having positive ground and what compelled manufactorors to switch to negative ground?
If I recall electrical theory right the voltage flows from positive to negative while current flows from negative to positive.
Any thoughts?

If I recall electrical theory right, voltage does not flow at all, it is just a potential. Only the current flows.

[w4jeh]

John is correct. Current flow is the flow of electrons through a conductor from one point to another. Current flows from negative to positive in A DC circuit.

Voltage doesn't "flow" it's the potential difference between two points in a circuit.

Jim

[scooder]

Originally Posted by Karl

My Series V Sunbeam Alpine was the first Series of Alpines to go negative earth in 1967-Karl

You got an Alpine, nice. I work predominantly on British sports cars from late 50's through late 70's, just finishing an engine rebuild on a MGC, now out of all of these Brits the Alpine is the one car that feels just perfect when I'm sat behind the wheel. Everything is in the right place for me, always makes me grin like an idiot when I'm "road testing" them, they just fit me perfectly. I'm 5'3", so take that into account.
Don't get me wrong, a nice 4.2 early E type Jag (XKE) is an amazing thing to drive, everyone should have a drive of these in there life, but the Alpine just fits me perfectly. And the Alpine looks right from every angle. Much better than the regular MGB'S.
Sorry for going off topic.
Martin.

[JSeery]

I'll take a crack at this, however, remember going in it is a confusing if you are not familiar with electronics!

In the early years of electric theory and before atomic theory was well understood, it was established that current flowed from a positive source to a negative. Based on this concept the theories of electricity, the basic formulas and symbols were developed. As the atomic nature of mater became better understood it was realized that what was called current was actually the movement of free electrons and that electrons have a negative charge. Free electrons move from a negative source to a positive source. There was a period of time when this flow from negative to positive was considered an important factor and there were attempts to account for it. However because electric/electronic theory was already established and the realization that actual electron movement was not that important in most applications it was determined to keep the original convention of current flow as positive to negative. This is now referred to as Conventional Current Flow and it what is used in almost all references to current flow in a circuit. The other term used is Electron Flow which refers to the actual direction electrons flow in a circuit. The true electron flow is normally only used in explaining specific circuit characteristics.

Current is conducted through some materials and not others. One of the characteristic of conductors is the way the outer part (shell) of the atoms of these materials behave. In most conductors, the electrons are loosely connected to any given atoms nucleus and tend to float or drift around between different atoms (something referred to as an electron cloud). This allows materials such as metals to be shaped. When a metal is hit or bent the atoms can fairly easily reposition themselves as opposed to a rigid outer shell with the electrons held tightly in place (this is really referring to the relationship between the atoms in a material and not to the individual atom). This same property make metals good conductor of current as the electrons can easily move from atom to atom along the conductor. These electrons carry a negative charge and move away from a negative source and toward a positive source, thus the current is moving from the negative to the positive.

It was eventually determined that this actual flow from negative to positive was not an important factor in normal day to day electrical practice. The idea was that it could just as easily be looked at as the “holes” left by the missing electrons (leaving a positive charge to the atom) moving from positive to negative. Now almost everything matched with the original theories and all was well with the world. So, if you are referring to the actual movement of electrons in a circuit it is negative to positive. If you are referring to what is now called Conventional Current Flow, it is from positive to negative.

[Binx]

Essentially the old argument about lightning going up from or down to earth.

Lonnie

[rotorwrench]

When voltages get to the amount in a lightning bolt, they can go anywhere they want to. I just learned to stay out of their way because the ones that hit humans don't care which way they come from.

[COE Dan]

Originally Posted by rotorwrench

... The 6-volt system is taxed by any resistance in an electrical system. This is why the average wiring is 16 to 10 wire gauge instead of the smaller gauges used in the 12-volt systems...

In a 12-volt system it's not necessary. Resistance has a much lower effect than with the lower voltages.

6V systems need double the amperage of a 12V system to accomplish the same amount of work. That's why 6V systems require larger wires to carry the increased current load, not to overcome system resistance. However, the statement that 12V systems are less affected by resistance change is correct.

Using Ohms law (I won't do the math here), one will find that a 6V system is 4 times as sensitive to resistance changes compared to a 12V system.

Also, as JSeery suggests, electron flow is irrelevant for our purposes. Conventional Current Flow makes sense in that most folks equate “positive” with a value greater than something “negative”, probably largely based on the fact that “negative ground” has been common for so long that to most people “negative ground” means “zero voltage”. All of our math and measurement conventions reflect this Conventional Current Flow idea.

However, even current flow really doesn't matter as it is a mathematical convention based upon standard assumptions. If you randomly assume current flows in one direction for a particular circuit, conduct an analysis, and find the resultant current value is a negative number, that merely means your initial assumption of current flow direction was opposite of the convention. The current's magnitude (value) will be identical regardless of the mathematical sign.

[rotorwrench]

Its actually for both reasons. You can use an 18 guage wire in a 6-volt system as long as it's real short. Most electrical engineers just played it safe and used wiring that would have both lower resistance and higher current capacity. These old systems were only 35 amp max. A lot of early era cars burned up due to wiring problems back in the day. That and a lot of wood construction didn't help either. In aviation, they went to 24-volt so they can use even smaller wire gauge to save weight. Long wire runs have to use a larger gauge due to the resistance drop.

[terry]

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Something to remember in this thread is that some devices need electricity moving the right way in order to work properly in our old cars. LED lights, transisters?, etc. can be polarity sensitive. Most of these modern day devices are made for negative ground. Terry

[Mike51Merc]

Originally Posted by terry

Something to remember in this thread is that some devices need electricity moving the right way in order to work properly in our old cars. LED lights, transisters?, etc. can be polarity sensitive. Most of these modern day devices are made for negative ground. Terry

This is true, and diodes act as one-way valves based on polarity.

I think all-in-all it doesn't really matter, but once you choose you have to stick with your choice, especially in modern cars.

[Bill S]

The current flow from pos to neg is the flow of holes in the valiance of the electron. Electron flow is neg to pos.
In old days engineers talked about current flow. That was pos to neg. When I started in electronics I worked for an older engineer. Thus he would always talked current flow. I had to readjust my thinking. I Had learned electron flow.

[JSeery]

Originally Posted by Bill S

The current flow from pos to neg is the flow of holes in the valiance of the electron. Electron flow is neg to pos.
In old days engineers talked about current flow. That was pos to neg. When I started in electronics I worked for an older engineer. Thus he would always talked current flow. I had to readjust my thinking. I Had learned electron flow.

Yep, except there is no real flow, it is just a convention used. When you say "current flow" you are referring to "conventional current flow" which for all practical purposes is a made up term. The electrons flow counter to conventional current flow, the positive ions ("holes") don't flow through the wires. For almost all automotive applications and especially the older ones all of this is of very little concern and only confusing to most people. It is best to just go with the conventional current flow, positive to negative and not get to concerned about what is going on at the atomic partial level.