Negative Ground vs Positive Ground History Question.

[Wotname]

Does any know (or at least have an opinion ) why the world switched from using a positive ground to the now common negative ground.

I always thought I knew why (see below) but after recently asking google the question, I am not so sure my opinions on the matter are correct. I reckon there are enough learned folk on CF that actually know why this change occurred so here is their chance to settle the matter decisively .

FWIW, here are my thoughts on the matter.

• The concept orginiated with car manufacturers wanting to use the metal chasis as one leg of the DC electrical circuit.
• Initially it didn't matter as the electical aspects of early cars were basic; generator and lights, latter starter motors etc.
• Early wiring was cloth and varnish insulated and it was found that when the varnish broke down, the insulation was leaky especially when damp. Thus current flow occured even when the circuit was switched off. The negative side of the circuit always corrodes the fastest so it was "better" to have the wiring corrode rather than the chasis as the wiring was very replacable.
• When silicon based diodes were made strong enough to handle decent currents, the manufacturing technolgy was that the case was negative. As the case was part of the heatsink, alternators had to have the case as the negative side. By then, rubber and PVC were common insulators that didn't break down as readility so a negative chasis made more sense.

Now this might be way off the mark but I would like to hear any and all viewpoints. One thing that I am sure of is that we didn't arrive at the current system of using a negative ground by whim or accident.

Edit - pun not intended

[Mirage35]

Interesting question. I don't know the answer but now you've made me curious.

One of my first cars was a 6 volt positive ground system. (I'm not in fact quite that old; the car was built three years before I was born.) One notable difference: it had a generator, not an alternator. PITA because at idle it didn't have enough output to charge the battery.

Maybe something in the switch to alternators and other advances made negative ground an advantage?

[Mirage35]

Reading your last bullet point in more detail, you seem to be on the same track.

[Viking Sailor]

It had to do with the evolution of the vacuum tube. As the complexity of the vacuum tube and the surrounding circuit design increased it became more efficient to use a negative ground and a positive plate supply. When tube based radios were installed in cars it was much simpler to tie the negative battery terminal to the chassis then to "float" the radio on a positive ground.

[LakeSuperior]

FWIW, current in a circuit flows from negative to positive because the electrons are the actual charge carriers.

[continuouswave]

I believe that use of a positive ground was introduced by telephone systems. By making the voltage carried on the telephone wires -48 Volts with respect to Earth, the potential (pun intended) for galvanic corrosion was reduced.

[Wotname]

Originally Posted by AnglaisInHull

Interesting question. I don't know the answer but now you've made me curious.

One of my first cars was a 6 volt positive ground system. (I'm not in fact quite that old; the car was built three years before I was born.) One notable difference: it had a generator, not an alternator. PITA because at idle it didn't have enough output to charge the battery.

Maybe something in the switch to alternators and other advances made negative ground an advantage?

Originally Posted by AnglaisInHull

Reading your last bullet point in more detail, you seem to be on the same track.

I agree .

Prior to the alternator, it didn't matter to much for the generator or starter motor. They could easily be reconfigured to either positive or negative ground simply by "flashing" the field coils. Both rely of the residual magnetism of the field coils for their operation. The residual magnetism of the field coils can be simply changed by applying the desired potential across them for a second or two.

The alternator doesn't care what the residual magnetism of the field coils is as the output is AC. The diode stack that converts the AC to DC is the limiting factor. If the outer conductor of the diode is negative, then the alternator has a negative case. I think (but don't know) that all early high current diodes all had a negative
outer body which was due to the technology of the time.

However I'm not sure exactly why positive grounds were used prior to this time.

[Wotname]

Originally Posted by continuouswave

I believe that use of a positive ground was introduced by telephone systems. By making the voltage carried on the telephone wires -48 Volts with respect to Earth, the potential (pun intended) for galvanic corrosion was reduced.

If you are referring to early telegraph systems, I think you are correct as far as they used a positive earth. However I don't understand the advantage of reduced galvanic corrosion. Exactly what was being protected??? The wires that were "above"ground potential or some other aspect. My understanding is that the negative conductor suffers more corrosion than the positive conductor in a floating circuit. If this is the case, then the negative wires must have suffered higher rates of galvanic corrosion than those used in a negative ground configuration.

????

Later telephony systems (post WWII) use fully floating circuitry but I recall the negative side was always more corroded than the positive side. I replaced a lot of household telephone sockets in the 70's due to corroded negative contacts

[Wotname]

Originally Posted by Viking Sailor

It had to do with the evolution of the vacuum tube. As the complexity of the vacuum tube and the surrounding circuit design increased it became more efficient to use a negative ground and a positive plate supply. When tube based radios were installed in cars it was much simpler to tie the negative battery terminal to the chassis then to "float" the radio on a positive ground.

I hear you and thank you for this considered opinion. At this stage I don't agree with it but perhaps I'm wrong... .

Given the requirements for HT voltage (600+ V) and the necessary inverters to get 12 VDC to HT voltages, I think the ground aspects were inconsequential. I recall the tube radios that I are familiar with were all in positive ground cars and by the time negative ground cars were common, the world had switched to semiconductor technology.

But these are my thoughts rather than hard facts so I remain open to your considerations.

FWIW, all aircraft I have ever seen were negative ground including the ones with tube technology radios; many had (and still have) generators. Not sure if this is relevant or not...

[noelex 77]

On a positive note, at least we have a convention that is almost universalły followed.

Cars, trucks, boats, planes, etc, etc are all, or nearly all, negatively ground irrespective of the country of manufacture.

[Wotname]

Originally Posted by LakeSuperior

FWIW, current in a circuit flows from negative to positive because the electrons are the actual charge carriers.

I reckon this aspect is a red herring...

Yes, the electron is the charge carrier when considering current flow in a conductor. And yes, it does "move" from the negative pole to the positive pole outside the source but one must remember than inside the source the opposite is true.

But what of current flow in a fluid, here it is positive and negatively charged ions; which way do they move outside and inside a source of PD.

But thanks for contributing, your post is appreciated along with every other post.

It all helps in understanding how electricity works

[Wotname]

Originally Posted by noelex 77

On a positive note, at least we have a convention that is almost universalły followed.

This is true!

Wotie now goes to sleep trying to think of DC systems that currently use a positive ground reference :big grin:

And yeah, pun intended .

[Rapanui]

I remember asking this question why positive earth when I first started playing with cars and bikes. The answer I was given by a mechanic was that it was done to reduce the erosion of the smaller spark plug centre pin by making it the cathode. I suspect in reality, it was a combination of a number of factors as outlined above.

[Zil]

In the USA, Ford used positive ground up until 12 volt systems came into being. Sometime in the late 1950's. Ford's idea was when point break coil ignition, the positive ground made better spark at the plugs. GM, Chrysler, Willies, Studebaker, all had negative ground, even when 6 volts. Volkswagen continued with positive ground well into the 1960's. Negative/positive had no meaning until electric lights, ignition, and eventually starter replaced magnetos. Cadillac 1910. This information is from my memory, so should be that reliable.

[SteveInMD]

I've always wondered why Beneteaus have not only a standard battery switch on the positive side, but also have a battery switch on the negative side too. Can anyone explain that one?