Positive vs Negative ground. Is there an engineering reason?

[m-mman]

No shortage of questions “Is my car positive or negative ground?”  

Confusing because The industry was never consistent.  Model T vs A was swapped. 

A Dodge Brothers post I found said they were different north or south of the Canadian border for the same year. 
 

The manufacturers did what they did, but is there an engineering reason?  
 

Electrons flow from negative to positive….but does one ground or another; give more amps? Charge easier? Give a hotter spark? 
 

Voltage certainly affects amperage draw and wire size.

But Is there any science or performance reason why they would select one ground or the other? 

[Mark Shaw]

I don't think so. 

However, manufacturers often make their products just different enough to force their customers to buy parts only from the OEM.

 

[John Byrd]

I think it was a "make more money" reason as all my positive ground vehicles batteries ALWAYS lasted much longer than the negative ground ones. Can't sell batteries if they don't "go dead", lol.

[Frank DuVal]

12 hours ago, m-mman said:

Electrons flow from negative to positive….but does one ground or another; give more amps? Charge easier? Give a hotter spark? 

You are right on, maybe, spark fires easier (less voltage required) when the spark plug center tip fires to the larger "ground" electrode. So, ignition systems (well, that I know of) had the center electrode be negative with respect to the shell of the plug, until HEI came along with enough volts to overcome that issue and now Buick has sold waste spark engines [where a pair of plugs/cylinders fire together so one is reverse polarity of the other], (along with other manufacturers) for over 30 years.

 

That means the center tip of the spark plug was negative with respect to the threaded part, i.e. positive ground. Now, you can have that polarity stay the same and change the primary polarity, but I guess some manufacturers liked all the circuits to have the same polarity and made the primary (battery side) positive ground.

 

36 minutes ago, John Byrd said:

I think it was a "make more money" reason as all my positive ground vehicles batteries ALWAYS lasted much longer than the negative ground ones. Can't sell batteries if they don't "go dead", lol.

Makes no sense from an electron's view. And not my experience with my vehicles.

[JACK M]

1 hour ago, John Byrd said:

positive ground vehicles batteries ALWAYS lasted much longer than the negative ground ones.

And all this time I just figured that old six-volt batteries were just better batteries, since I have been pleasantly surprised a few times.

[Rusty_OToole]

On old cars the positive side corrodes faster than the negative and a ground strap is easier and cheaper to replace. This is not such a problem these days, batteries do not seem to gas and corrode like the old ones.

 

Other than that I don't know any difference. Which I suppose is why some did one way, some the other.

[37_Roadmaster_C]

I am retired out of the electrical and electronics field.  I am NOT an engineer nor do I have any engineering specific education.  In my practical experience, there is no reason, I know of, that would make any difference. From a voltage, current or power standpoint both are the same. The only reason it might, I stress Might, make any difference is if the product had to work in conjunction with other pieces of equipment. in a combined system. A vehicle is a stand alone assembly so there is no need to match anything.  With that said, I think it was simply at the whim of the engineer designing the electrical system for the vehicle.  A lot of people think electrical current (electrons) flow from positive to negative. but as @m-mmansaid, current actually flows from negative to positive so who knows??????????

[31nash880]

At some point in my past I recall a mention of current flow causing rust. Maybe at ground points? 

[sarookha]

1 hour ago, 31nash880 said:

At some point in my past I recall a mention of current flow causing rust. Maybe at ground points? 

Free electrons are required for the oxidation chemistry that leads to rust.  That's why a sacrificial anode works (the zinc in the anode soaks up the free electrons even more eagerly than iron atoms do, and the zinc corrodes instead of your sheet metal.  Not just at ground points.

[Frank DuVal]

1 hour ago, sarookha said:

That's why a sacrificial anode works (the zinc in the anode soaks up the free electrons even more eagerly than iron atoms do, and the zinc corrodes instead of your sheet metal. 

I guess if you sink your car in water or moist dirt for the electrons to flow then a sacrificial anode would be helpful, but on dry land, no. There needs to be current flow through the zinc to work.

[lozrocks]

Yes there is a logical reason why cars switched to negative ground.

And it's all to do with setting a standard by which all manufacturers could follow. It was driven by the Japanese starting in the late 1940s to early 1950s and the development of the huge electronics industry in Japan. And in turn the development of semiconductors. A standard was introduced where all electronic devices would use a negative ground. TV and radio manufacturers accepted the standard early. By the mid 1950s the automotive industry was dragged into using the standard which would allow more electronic creature comforts (like hifi radio) to be fitted to cars.

It really doesn't have anything to do with current flow or sacrificial anodes.

As a side note: electrons flow from negative to positive, but conventional current flows from positive to negative.

[Restorer32]

Actually, electrons do not "flow" at all.  Picture a line of people. Person #1 punches #2, #2 punches #3, #3 punches #4 and so on down the line. 

[EmTee]

[Ben Bruce aka First Born]

Just now, EmTee said:

 

 Agree.

 

  Ben

[sarookha]

10 hours ago, Frank DuVal said:

I guess if you sink your car in water or moist dirt for the electrons to flow then a sacrificial anode would be helpful, but on dry land, no. There needs to be current flow through the zinc to work.

Correct, I was using the sacrificial anode as an explanation to 31Nash880's question about rust, not suggesting they should be installed on our cars.  However, I have wondered why folks in the rust belt don't bury one (the anode, not the car!) in their yard, and run a cable to the garage to hook to the car when parked.  Too much trouble for a cheap driver, perhaps, but for a special vehicle, it would probably help.

[Farmallregular]

In 47 years as a practicing electrical engineer I've heard several theories, but have never seen any definitive data to support one way or the other.  The corrosion idea MAY have some merit, but obviously isn't a definitive reason or we'd still all be positive ground...remember, the "ground" on an automobile has nothing to do with the physical earth, but is nothing more than a reference point, and electronics can be made to work properly with the reference wherever you want it to be.

 

There' a lot to be said for standardization, and in this case I suspect the advantages of standardization overwhelmed whatever technical reasons there may or may not have been.

 

Keith

 

[m-mman]

Standardization of grounds is a good thing. Guess there was no reason for one or the other than some engineers flipping a coin.  
 

Especially the swap between the Model T and A. I wonder if that was Henry’s choice? Or maybe an engineer from a positive ground company came in and joined the design team? 
 

As noted below: Cadillac using positive ground while other GM used negative seems wasteful. 

 

 

This comes from the Ford Barn:

 

Why Negative Ground?

A recent forum discussion thread on the fordbarn.com web site motivated me to go back and look again at an article in the Skinned Knuckles magazine. The article, "Why Negative Ground?" was in the September 2009 issue, #398. The simple question about a relatively modern occurrence was asked by a reader: Why did all remaining positive-ground U.S. manufacturers switch to negative-ground in 1956? After extensive research seeking an answer, the frustrated editor concludes,

"Much as I would like to announce that we have an answer, unfortunately just the opposite is true. Not only have I not obtained facts, but I am also puzzled beyond belief that the wide variety of automotive historians and curators whom I questioned could not come with a factual answer."

One U.K. electrical engineer and museum curator who was queried on the subject replied, "You have opened a can of worms..."

The SK article includes a table showing ground usage by 35 car models since 1932. Twenty five of those used positive ground for at least part of their existence. The various models that became part of GM, except for Cadillac, always used negative ground, as did Duesenberg, Essex, Stutz, and Reo. Cadillac switched from positive to negative ground after WWII. Hudson switched from negative to positive ground in 1934, and then back to negative in 1956. The "universal" switch to negative ground never occurred in the U.K. Nash Metropolitans remained positive ground, and allegedly some US car models made for export to the U.K. are still set up with positive ground.

The various creative, speculative or bogus rationales supporting one or the other grounding usage that have been offered over the years, including the corrosion thing, are briefly reviewed. The fact is that in 1956 there was a sudden consensus that it would be a good idea to standardize, but exactly how and why that consensus emerged at that moment in time remains puzzlingly mysterious.

I think it's clear that there really is no strong argument to be made one way or the other, but standardization is a good idea, and, happily, it came to pass! Too bad Ford was on the wrong side of history, but it's no big deal.

[Oldtech]

Electronic Schematics are normally drawn up using "positive logic" meaning the traced flow is from pos. to neg.  ( that is, back when components were individual and you could actually check one). 

They never concerned themselves with which way the current may actually be travelling.  I don't think it makes ANY difference.

[DFeeney]

I thought in the past ,testing was done under laboratory conditions on this subject. . The engine received about 10% higher spark when the system was negative ground all other things being equal.   Is this just "Folk Lore"?

[PFitz]

44 minutes ago, DFeeney said:

I thought in the past ,testing was done under laboratory conditions on this subject. . The engine received about 10% higher spark when the system was negative ground all other things being equal.   Is this just "Folk Lore"?

From what I've read, it has to do with how electrons flow better from a hot spark plug center electrode to the cooler plug ground.  Supposedly gives 10-15% better spark if the spark is jumping from center electrode to ground. Difference is generally only noticeable when engine is under loads such as uphill. 

 

One recommended test for curing high-speed misfires is the reverse the polarity of the ignition coil. 

 

Paul

Edited December 1, 2022 by PFitz (see edit history)

[Frank DuVal]

20 hours ago, lozrocks said:

A standard was introduced where all electronic devices would use a negative ground. TV and radio manufacturers accepted the standard early.

Nope. Many transistor circuits have positive ground! We do have NPN and PNP transistors.... so either grounding system works for solid state.

 

Many cars had negative ground 6 volt systems waaaay before the transistor was invented.  See Buick and Chevrolet.

[Frank DuVal]

13 hours ago, sarookha said:

However, I have wondered why folks in the rust belt don't bury one (the anode, not the car!) in their yard, and run a cable to the garage to hook to the car when parked. 

Because there HAS to be current flow from the zinc back to the steel to complete the circuit. Just hooking a wire from the steel to the zinc is not a complete circuit, and without a complete circuit, electrons can not flow. In the EARTH the electrons flow through the earth to return to the steel tank, completing the circuit.

[Bloo]

1 minute ago, Frank DuVal said:

Many transistor circuits have positive ground! We do have NPN and PNP transistors.... so either grounding system works for solid state.

That is especially true of early solid state electronics. PNP Germanium transistors were the most common by far, and they adapt much better to a positive ground. Most solid state equipment of that era was positive ground internally (on the circuit boards), no matter how it was configured on the outside.

 

[Frank DuVal]

8 hours ago, PFitz said:

From what I've read, it has to do with how electrons flow better from a hot spark plug center electrode to the cooler plug ground.  Supposedly gives 10-15% better spark if the spark is jumping from center electrode to ground. Difference is generally only noticeable when engine is under loads such as uphill. 

Man, if only someone had mentioned this.

 

On 11/30/2022 at 2:42 PM, Frank DuVal said:

You are right on, maybe, spark fires easier (less voltage required) when the spark plug center tip fires to the larger "ground" electrode.

Oh, someone did!

[Farmallregular]

A little more info on the spark polarity issue.  Electrons are emitted easier from a hot surface, and since the center electrode of a spark plug is hotter than the "ground" electrode, it's easier to initiate a spark if the center electrode is negative.  For those of you old enough to remember vacuum tubes, the glowing filaments created a hot cathode which emitted electrons.  

 

In an engine, the polarity of the spark is determined by the relative phasing of the windings in the coil, so that the high voltage output is negative with respect to "ground", even with the primary battery voltage being positive with respect to "ground" in a negative ground system.   An ignition coil designed for a positive ground system will have different phasing than one designed for a negative ground system.  Using a coil designed for a negative ground system with a positive ground by reversing the primary connections will work, with a small reduction in output.

 

Arranging the ignition to provide a negative pulse to the spark plugs has no bearing on battery polarity.

 

Keith

 

[DFeeney]

Many years ago when I started in the trade I learned the phrase, "Ground is Ground the World around"

[m-mman]

The comments about grounds and electronic circuits.  
 

In the late 70s a friend bought a 1955 Mercury. (a 20 year old car).  55 Mercs were factory 6 volt positive ground.  The car ran well and everything worked except the radio. 
 

Strangely the radio only worked if you removed one of battery cables(?). 
He said that he invested more time into troubleshooting than he wanted to admit before he realized that the battery was backwards.  (Negative ground on purchase) 

 

He turned it around, polarized the generator, fired it up and everything worked including the radio.  
I never understood how that worked electrically. 

[Ben Bruce aka First Born]

I recently watched a You Tube video of a fellow getting a 1950 Buick running and driving.  Now all Buicks, I believe, are neg ground.  As far back as I have worked on them anyway, .     This fellows 1950 is hooked up positive ground.  When he bought it.  The flat woven ground cable is used for the starter cable. ALL TAPE COVERED.

 

  Ben

[Grimy]

31 minutes ago, Ben Bruce aka First Born said:

I recently watched a You Tube video of a fellow getting a 1950 Buick running and driving.  Now all Buicks, I believe, are neg ground.  As far back as I have worked on them anyway, .     This fellows 1950 is hooked up positive ground.  When he bought it.  The flat woven ground cable is used for the starter cable. ALL TAPE COVERED.

 

  Ben

Where is the "aarrrggghhh" emoji when we really need it?

[37_Roadmaster_C]

4 hours ago, DFeeney said:

Many years ago when I started in the trade I learned the phrase, "Ground is Ground the World around"

This is a 100% true statement!  The term ground has been grossly skewed, at least in the US. The proper term, as used in Europe, would be EARTH.   A TRUE GROUND or EARTH connection is a safety connection ONLY!!!  It is what keeps you from being zapped when you touch the case of something which has an internal failure that makes the case have voltage on it. A true ground, by definition is a "Non current carrying conductor" by National Electric Code rules.  In the US, we have skewed the term in some industries to equate to "Common Connection" like the chassis of an automobile.

Hence the quote above.

 

43 minutes ago, m-mman said:

The comments about grounds and electronic circuits.  
 

In the late 70s a friend bought a 1955 Mercury. (a 20 year old car).  55 Mercs were factory 6 volt positive ground.  The car ran well and everything worked except the radio. 
 

Strangely the radio only worked if you removed one of battery cables(?). 
He said that he invested more time into troubleshooting than he wanted to admit before he realized that the battery was backwards.  (Negative ground on purchase) 

 

He turned it around, polarized the generator, fired it up and everything worked including the radio.  
I never understood how that worked electrically. 

I am almost 100% sure that what was happening is that when the battery was disconnected, "When the car was running", the generator picked up the load and in some way with the correct polarity. The actual question is why was there no smoke from the wiring or the battery ay the generator "Battery" cable would have had a lot of current flowing through it.

 

35 minutes ago, Ben Bruce aka First Born said:

I recently watched a You Tube video of a fellow getting a 1950 Buick running and driving.  Now all Buicks, I believe, are neg ground.  As far back as I have worked on them anyway, .     This fellows 1950 is hooked up positive ground.  When he bought it.  The flat woven ground cable is used for the starter cable. ALL TAPE COVERED.

 

  Ben

Ah for the luck of children and fools..................

 

[Frank DuVal]

The phrase I heard years ago was Green is Ground the whole earth round. Of course in many areas it is with a yellow stripe...

 

Earth and Ground are the same to me. Unless I have ground some beans for coffee....

 

And why is ground a skewed term when it comes to chassis ground (chassis earth for Brits)? This term has been in use since almost forever (well the electronic schematics forever). If anything, the NEC skewed it to also mean a safety connection back to the source.

[joe_padavano]

This article is the first one I've read that actually makes some sense.

 

https://mgaguru.com/mgtech/electric/et098.htm

[Frank DuVal]

Right up until they said:

 

" To be nice we also swap the primary wires on the ignition coil so the spark still jumps the same direction across the spark plug gaps (mostly for radio static reduction). "

 

What? The reason is for performance! As stated earlier, spark plugs perform better positive ground until HEI overcame that issue. Now, I guess an argument could be made that trying to jump the gap with the wrong polarity makes the voltage rise, therefore static increases.... OK, OK!😁

[Bloo]

The next common electronic gadget for cars was the triode bridge in the alternator, circa early 60's. Early alternators used silicon plate rectifiers that could be connected for either positive or negative grounding, so some early alternators were made for positive ground applications. When silicon diodes were developed with sufficient current capacity for alternator rectifiers, all alternators were quickly redesigned to use diodes. This is when all alternators became negative ground, and all cars using them were built with electrical return path connected to battery negative.

 

WHAT?!

 

 

[37_Roadmaster_C]

10 hours ago, Frank DuVal said:

And why is ground a skewed term when it comes to chassis ground (chassis earth for Brits)? This term has been in use since almost forever (well the electronic schematics forever). If anything, the NEC skewed it to also mean a safety connection back to the source.

Because "earth ground" is the ONLY true "Ground" reference.  The chassis of a vehicle has NO intentional electrical connection to earth ground, however by skewing the term "ground" to actually mean "chassis common", we now have what people mean when they say "ground". It is just a matter of words. As long as the people in the conversation are on the same page it matters not.

   I come from a electric power systems industry and a broadcast and communications industry background. In these two careers, the term "Ground", ment very very different things and I can carry on a discussion equally  well in both areas, however, if both fields come up at the same time, it is mandatory to define power system and antenna "ground" as meaning "earth ground" and electronic equipment systems "ground" as meaning "common connection" point. Now to really confuse things, both grounds CAN be the same electrical potential and the same conduction path.  Clear as mud made from the ground, right 😇????

[intimeold]

Let me add this to the conversation.  This is not my theory; but I saw this printed along time ago.  Don't beat me up; I am just adding this, to the talk.

 

I do Not know, who the author of this theory was.

 

"Henry Ford and Thomas Edison were great friends. Henry thought Thomas was the smartest person who ever lived. Thomas was a believer of direct current, except Westinghouse beat him out for electrical distribution in the cities, with alternating current.

Mr Edison thought electrons moved from negative to positive and because of the theory felt here would be less metal transfer in ignition points and other contacts in automobiles with a negative ground system.
These two genius people had a shop above the power house at Henry's Fairlane estate where they played with all kinds of experiments".
 

[Frank DuVal]

  Quote

Quote

The next common electronic gadget for cars was the triode bridge in the alternator, circa early 60's. Early alternators used silicon plate rectifiers that could be connected for either positive or negative grounding, so some early alternators were made for positive ground applications. When silicon diodes were developed with sufficient current capacity for alternator rectifiers, all alternators were quickly redesigned to use diodes. This is when all alternators became negative ground, and all cars using them were built with electrical return path connected to battery negative.

 

 

WHAT?! 

Unquote

 

Yep, let's sort through this. Instead of silicon plate rectifiers, they are selenium rectifiers with plates designed on them for heat dissipation. Work OK, have more voltage drop than a silicon diode (which is .6 volts) and stink like rotten eggs when they fail. They are bulky because of the plates.

 

Triode bridges can be made "pointing in or pointing out" (common cathode or common anode connection point), i.e. they can be built for negative or positive ground use. Same with the six heat sinked diodes that carry the charging current inside the alternator, changing that three phase AC current to DC internally. Three point away from the case of the diode (case is anode), three point towards the case of the diode (case is cathode). So, easy to make it a positive ground alternator, just swap the six diodes and get another diode bridge "pointing" the correct way (or make your own, they are small amp diodes).

[lozrocks]

On 12/2/2022 at 2:18 PM, Frank DuVal said:

Nope. Many transistor circuits have positive ground! We do have NPN and PNP transistors.... so either grounding system works for solid state.

 

Many cars had negative ground 6 volt systems waaaay before the transistor was invented.  See Buick and Chevrolet.

NPN and PNP transistors both use negative ground. (or they can both use positive ground) Either ground will work for solid state systems. But once the standard was introduced and accepted by all manufacturers the positive ground circuits were phased out. Some early cars did use negative ground, nobody disputes that, but there are no later vehicles using positive ground.

The main reason the automotive industry moved to negative ground was to comply with the standard.

[Angelfish]

On 12/1/2022 at 4:57 AM, Restorer32 said:

Actually, electrons do not "flow" at all.  Picture a line of people. Person #1 punches #2, #2 punches #3, #3 punches #4 and so on down the line. 

You're thinking of McDonald's in Detroit.

[Frank DuVal]

On 12/1/2022 at 2:18 AM, lozrocks said:

A standard was introduced where all electronic devices would use a negative ground.

This is my issue. I have not seen a standard in the electronics industry that said to use negative ground. Sure the automotive industry settled on the negative ground system, with Britain dragging their feet well into the 60s. But not electronics industry. I’ve worked on many LV and HV DC systems designed in the last 15 years that were positive ground! Or both. 😉 (i.e. power supplies feeding systems with both + and - voltages above chassis).