Why are GND and 0V different ?

Why are GND and 0V different ?
Take a peek here...

The concept of electrical ground began when radio receiver sets were being
manufactured. At that time, many of the components were large and had to be
mounted firmly. Each set was built on a metal chassis. The power transformer,
tube sockets, i.f. transformers and tuning and filter capacitor(s) were riveted
or bolted to it. At that time, a power supply had a power output terminal and a
return terminal. The engineers decided that the chassis could be considered as
a big, fat wire. So they connected the return wire of each of the power supplies
to the chassis. Then every circuit wherever it was located would have a wire
connected to the chassis for the power supply returns. That saved a lot of wire,
made radios easier to build, better looking inside and cheaper. It was a
win, win situation. The circuits return connections became known as chassis
ground. Later the term was shortened to just ground. (Today, we use ground
planes on many of our PCB's. It's the same idea.) So that is where the power
supply ground came from. Now, it seems to be confusing to some if not many
newcomers to the hobby. Some think that every circuit MUST have a ground.
That is not true. This problem is reinforced by our use of ground symbols
on our schematic diagrams. Just imagine if you had to draw a complex
schematic without using ground symbols. Who could see the real circuit with
all those ground wires in place? What a mess that would be! So we take the
short cuts and use grounds. Another confusion seems to come from the use
of the same ground symbol for different power supplies. Not to worry, the
electrons know where they need to go, so they do not get lost. Maybe if
people think of the ground terminal or symbol as just a return to power
supply, the confusion would be eliminated.

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The "GND" connection on Arduino should be called "circuit common" or some such. I don't believe a point should be called "ground" if it is not connected with a low resistance conductor to the actual Earth.

100% agree +1

This confusion is caused by Americans not using the word Earth for mains wiring. In fact one editor of a book I wrote did not know what the word “mains” meant either.

Ground is the proper word to use for a circuits common reference point. So two peoples divided by a common language.

Just tell beginners that ground is not Earth and you normally do not connect ground to Earth although some instruments like an oscilloscope do. This causes problems if you try and measure mains voltages across say a resistor. Scopes go bang, there is a good video by our antipodean friend Dave, about this.

When I first started out a trick engineers used was to disconnect the Earth lead on a scope at the mains plug and leave the wire hanging out of the plug so you could see it was a floating instrument. Thanks to stupid bureaucrats with moulded sockets you can’t do that these days.

lastchancename:
Why are GND and 0V different ?
Take a peek here...
BEGINNERS: What is GROUND ? - Introductory Tutorials - Arduino Forum

What is mistakenly called "ground" should be correctly called "circuit common".

On a similar note, "Vcc" and "Vdd" are casually used interchangably by many people. This is a mistake.

An Arduino board, for example, the MCU uses mosfets which have drains, not collectors. Therefore, the power input is "Vdd" (d as in drain), not "Vcc" (c as in collector).

Can you dig it? I knew that you could.

lastchancename:
Please
use
paragraphs
to make
yourself
more
readable !

This board has THE WORST editor I have ever encountered. During entering text, it discards extra newlines that people use to create readable paragraphs. A preview and an edit are required to split the resulting solid block of text back into paragraphs.
Plus, every minute or so (maybe the "draft auto save"?) spews something out that causes text to get repeated, requiring further editing (as well as constantly checking to see if each word got mangled).
Watch this: I will type without fixing the result so you can see what I mean:
"I believe ththat tths nation should comcommit itself to acheivinacheiving the goal, berore thisthis decade is out, of llanding a man on the moomoomoon and returningreturn him safely to earthrth. (President John F. KennedyedyKennedyedy,, May 25, 1961).
Painful to post here....

(above was properly paragraphed. Now, the proper result after editing):

This board has THE WORST editor I have ever encountered. During entering text, it discards extra newlines that people use to create readable paragraphs.

A preview and an edit are required to split the resulting solid block of text back into paragraphs.

Plus, every minute or so (maybe the "draft auto save"?) spews something out that causes text to get repeated, requiring further editing (as well as constantly checking to see if each word got mangled).

Watch this: I will type without fixing the result so you can see what I mean:

"I believe ththat tths nation should comcommit itself to acheivinacheiving the goal, berore thisthis decade is out, of llanding a man on the moomoomoon and returningreturn him safely to earthrth. (President John F. KennedyedyKennedyedy,, May 25, 1961).

Painful to post here....

jackrobot:
GND is the common reference point with the reference to which the voltage of other points are measured.

GND can lie at any potential other than zero but when other nodes are measured with respect to GND is considered to be at 0V

You may call circuit common "GND" if you wish. But it's still wrong.

Grumpy_Mike:
This confusion is caused by Americans not using the word Earth for mains wiring. In fact one editor of a book I wrote did not know what the word “mains” meant either.

Ground is the proper word to use for a circuits common reference point. So two peoples divided by a common language.

Just tell beginners that ground is not Earth and you normally do not connect ground to Earth although some instruments like an oscilloscope do. This causes problems if you try and measure mains voltages across say a resistor. Scopes go bang, there is a good video by our antipodean friend Dave, about this.

When I first started out a trick engineers used was to disconnect the Earth lead on a scope at the mains plug and leave the wire hanging out of the plug so you could see it was a floating instrument. Thanks to stupid bureaucrats with moulded sockets you can’t do that these days.

UK to US:

valve == tube
earth == ground
moulded == molded
colour == color

etc....

I assert that the US spelling is superior because it uses less letters! :slight_smile:

(well except for ground... wait! I meant "GND"!). :slight_smile:

GND has no defined relationship to negative or zero volts - UNLESS they have been tied together or other bonding within the power supply lifts the supply to some other potential.

lastchancename:
GND has no defined relationship to negative or zero volts - UNLESS they have been tied together or other bonding within the power supply lifts the supply to some other potential.

Right.

UK to US:

valve == tube
earth == ground
moulded == molded
colour == color

etc....

I assert that the US spelling is superior because it uses less letters!

Obviously the UK versions are better; having more letters makes them more precise :slight_smile:

... uses less letters!

I think you mean fewer letters! :slight_smile:

This is a good discussion, something that has been bothering me since I first joined this forum. I have been considering writing something to serve as a tutorial but never quite got it right. I do have some text I have occasionally pasted as an answer to questions on this subject. I have no doubt it can be improved. Here it is:

Earth (or ground) and 0V are often talked about as if they are the same thing. They are not, although, as they are often connected together, they can often be regarded as the same.
0V (zero volts, often incorrectly called “no volts”) is a point in a circuit designated by the circuit designer. 0V is the point to which all other voltages in the circuit are referenced unless otherwise stated. By definition 0V cannot be noisy. 0V is often but not always the most negative point in the circuit.
Earth is that muddy stuff outside. There is only one earth, if you are in any doubt, go outside and look around. In electrical terms when people say “earth” they really mean a connection to earth, often through the earth wire in the premises electrical distribution system.
An important thing to consider is that, while there is only one earth, there can be different connections to it and they are not all the same. In the UK (I don’t know about other countries) the earth connection in the building electrical distribution cabling is connected to the incoming neutral wire of the feed into the building before any fuse, meter or isolator. The neutral itself will be connected to the earth (the actual muddy stuff) at the distribution transformer. This means that an earth connection made to the building electrical earth might not be at the same voltage as an earth connection made to a metal stake pushed into the earth outside the building. As there is likely to be current flowing in the neutral back to the transformer then there will be a voltage drop across the neutral wire’s resistance. You can measure this voltage by putting a metal stake in the ground and measuring the voltage between the stake and the electrical system’s earth, most of the time this will be a few volts AC at most. However, if the transformer is hit by lighting then there is the possibility that the electrical system earth could be different from the earth outside the building by many tens or hundreds of thousands of volts, at least for a fraction of a second.
Some examples:
Something powered by batteries but not connected to anything else has a 0V but not an earth.
Many electronic devices, including Arduino, run off a power supply (the USB cable for example) that has its negative terminal connected to earth, so 0V and earth are connected and can be considered the same, and the supply is +5V (or whatever).
Many plug in mains adaptors do not have an earth connection (the earth pin is made of plastic), so anything running off them does not have an earth unless otherwise provided.
In my industry, telecoms, the positive pole of the supply is connected to earth, so the equipment runs on a -50V supply.
Analogue audio equipment typically runs off a split supply of -15V, 0V +15V, so it is the middle of the supply that is connected to earth, not the most negative part.

@Perry, You’re welcome to take a look at the link I posted in the OP, and draft an edit for that thread.
I was going to do it, but I’m physically offline a bit longer - so you may like to look at what started both here and there. I’m certainly open to clarification - even if the people that need it don’t ever read it !

I'm certainly open to clarification

It was all perfectly clear to me until I started to think about it, the more I thought about it the more I realised it was not so simple. GM's comment also, which I think are correct, also added to my doubts.

You're welcome to take a look at the link I posted in the OP.

I'll give it some thought.

Even if the people that need it don't ever read it !

A good tutorial will provide something to link to in response to the endlessly repeated questions about ground, earth and 0V.

PerryBebbington:
Obviously the UK versions are better; having more letters makes them more precise :slight_smile:
I think you mean fewer letters! :slight_smile:

You win this round! :slight_smile:

PerryBebbington:
In the UK (I don’t know about other countries) the earth connection in the building electrical distribution cabling is connected to the incoming neutral wire of the feed into the building before any fuse, meter or isolator. The neutral itself will be connected to the earth (the actual muddy stuff) at the distribution transformer.

In the US, it was like that (neutral tied to earth ground). The NEC (National Electrical Code) now requires that neutral be it's own conductor and ground be earth ground.

They even sell retrofit terminal blocks to separate neutral and ground in "old work" sub boxes to bring them up to code.

There’s a specific thread on ground and 0V in the Introductory Tutorial section.