Hi Gang! I get asked every now and then,  what is ground? Sometimes it's to  
Hi Gang! I get asked every now and then,  what is ground? Sometimes it's to  

do with household ground, this prong  and hole in your plug, sometimes it's  
do with household ground, this prong  and hole in your plug, sometimes it's  

about finding a good ground when  making something, and sometimes it's  
about finding a good ground when  making something, and sometimes it's  

ground in an electronic circuit. So  I thought I'd talk about each of these.
ground in an electronic circuit. So  I thought I'd talk about each of these.

Let's start with household ground.
Let's start with household ground.

In North America, this roundish hole is ground and so the prong on a plug  
In North America, this roundish hole is ground and so the prong on a plug  

that goes in it is the ground prong.
that goes in it is the ground prong.

But to understand that ground hole,  and prong, we first have to understand  
But to understand that ground hole,  and prong, we first have to understand  

the other two holes. In  North America they're called  
the other two holes. In  North America they're called  

HOT, and neutral, and the wires are  usually black and white.
HOT, and neutral, and the wires are  usually black and white.

They're what carry the electricity that  powers things.
They're what carry the electricity that  powers things.

Behind the hole called HOT, you'll find a wire  that runs behind the walls and
Behind the hole called HOT, you'll find a wire  that runs behind the walls and

eventually goes to a breaker  in you breaker panel.
eventually goes to a breaker  in you breaker panel.

From there the electricity goes  behind the breakers to one of these  
From there the electricity goes  behind the breakers to one of these  

thick black wires and then outside  your house to a transmission pole,
thick black wires and then outside  your house to a transmission pole,

and transformer somewhere. The  other hole, again, called neutral
and transformer somewhere. The  other hole, again, called neutral

here in North America, also goes to  that breaker panel but not to any breaker.
here in North America, also goes to  that breaker panel but not to any breaker.

Instead it goes to this metal  bar. From there the electricity
Instead it goes to this metal  bar. From there the electricity

goes along this thick white wire  and then outside your house to the  
goes along this thick white wire  and then outside your house to the  

same transmission pole and  the same transformer.
same transmission pole and  the same transformer.

Here that all is in a diagram.  This is the path for the HOT,
Here that all is in a diagram.  This is the path for the HOT,

or black wire, to the breaker and out  to the transformer. And this is the
or black wire, to the breaker and out  to the transformer. And this is the

path for the neutral, or white  wire, through the breaker panel and  
path for the neutral, or white  wire, through the breaker panel and  

out to the transformer. The other  side of the transformer is what  
out to the transformer. The other  side of the transformer is what  

continues on to the generating station. So where does the ground hole go?  
continues on to the generating station. So where does the ground hole go?  

It also has a wire that goes to the breaker panel and connects to  
It also has a wire that goes to the breaker panel and connects to  

this other metal bar, which is connected to the break panel's metal case.  
this other metal bar, which is connected to the break panel's metal case.  

And it's not clear with this panel, but somewhere the case is  
And it's not clear with this panel, but somewhere the case is  

connected to the neutral bar. Our diagram now looks like this,  
connected to the neutral bar. Our diagram now looks like this,  

with the ground wire going to a ground bar and then on to the neutral bar.
with the ground wire going to a ground bar and then on to the neutral bar.

But why is the ground wire connected  to the neutral like that?
But why is the ground wire connected  to the neutral like that?

That's in case you have a break in  the insulation covering a wire somewhere.
That's in case you have a break in  the insulation covering a wire somewhere.

That break can cause a  fault, such as in this microwave oven.
That break can cause a  fault, such as in this microwave oven.

Three wires enter the microwave oven. Those three wires are connected to the  
Three wires enter the microwave oven. Those three wires are connected to the  

three prongs on the plug, HOT, neutral and ground. As we said,  
three prongs on the plug, HOT, neutral and ground. As we said,  

the electricity flows through the HOT and neutral wires.
the electricity flows through the HOT and neutral wires.

The third wire is the ground wire. The ground wire is connected to the metal case  
The third wire is the ground wire. The ground wire is connected to the metal case  

and normally no electricity flows through it.
and normally no electricity flows through it.

We'll add the microwave oven to our  diagram. The hot and neutral wires  
We'll add the microwave oven to our  diagram. The hot and neutral wires  

go to the electronics, and the  ground wire connects to the case.  
go to the electronics, and the  ground wire connects to the case.  

But the case is not connected to  anything else, electricity won't flow on it
But the case is not connected to  anything else, electricity won't flow on it

because there's no return path. But what if the insulation around the  
because there's no return path. But what if the insulation around the  

HOT wire gets damaged, and the wire itself touches the metal case?  
HOT wire gets damaged, and the wire itself touches the metal case?  

The case is now connected to the  HOT wire. If you were to touch the case,
The case is now connected to the  HOT wire. If you were to touch the case,

you'd get a dangerous  shock. But luckily the ground
you'd get a dangerous  shock. But luckily the ground

wire is connected to the case. That  ground wire is a very low resistance  
wire is connected to the case. That  ground wire is a very low resistance  

path for the electricity and so it  will flow from the HOT, through the case,
path for the electricity and so it  will flow from the HOT, through the case,

through the ground wire, and  back panel where the ground is
through the ground wire, and  back panel where the ground is

connected to the neutral, and back  to the transformer, completing the  
connected to the neutral, and back  to the transformer, completing the  

circuit with the HOT wire there.  However, since that path is such low resistance,
circuit with the HOT wire there.  However, since that path is such low resistance,

the current will be very  high. And remember that the HOT
the current will be very  high. And remember that the HOT

path goes through a breaker in the  breaker panel. The current will be  
path goes through a breaker in the  breaker panel. The current will be  

high enough to trip that breaker,  disconnecting the power,
high enough to trip that breaker,  disconnecting the power,

and making it safe to touch the microwave  oven's case again.
and making it safe to touch the microwave  oven's case again.

Let's look at it again, but on the  diagram. The problem starts when  
Let's look at it again, but on the  diagram. The problem starts when  

insulation on the HOT wire breaks  and the wire touches the microwave oven's case.
insulation on the HOT wire breaks  and the wire touches the microwave oven's case.

Since the case is connected  to the ground wire, we now have
Since the case is connected  to the ground wire, we now have

this complete circuit along the  ground wire to the breaker panel,  
this complete circuit along the  ground wire to the breaker panel,  

then along the neutral wire onward  to the transformer on the pole,  
then along the neutral wire onward  to the transformer on the pole,  

through the transformer's coil, back  through the HOT, through the breaker,  
through the transformer's coil, back  through the HOT, through the breaker,  

and continuing to the HOT in the  microwave oven where it's touching the case.
and continuing to the HOT in the  microwave oven where it's touching the case.

There's very little resistance  along that circuit and so the
There's very little resistance  along that circuit and so the

electrical current will be very high,  high enough to trip the breaker,  
electrical current will be very high,  high enough to trip the breaker,  

which opens the circuit, making it  safe to touch the microwave oven's case again.
which opens the circuit, making it  safe to touch the microwave oven's case again.

But wait! None of that had anything to do with the Earth ground!
But wait! None of that had anything to do with the Earth ground!

Why is the wire called ground?
Why is the wire called ground?

Looking at the breaker panel again,  there's thick ground wire connected  
Looking at the breaker panel again,  there's thick ground wire connected  

to the neutral bar here that goes to  a metal rod buried in the ground,
to the neutral bar here that goes to  a metal rod buried in the ground,

called a ground rod, or to some other  metal that's buried in the Earth ground somewhere
called a ground rod, or to some other  metal that's buried in the Earth ground somewhere

like the metal pipe that brings cold water in from the city.
like the metal pipe that brings cold water in from the city.

And where the neutral wire goes to the transformer,
And where the neutral wire goes to the transformer,

there's another wire that goes down the pole  
there's another wire that goes down the pole  

to a ground rod there too. Now our diagram looks like this,  
to a ground rod there too. Now our diagram looks like this,  

with the thick bare wire from the breaker panel to Earth ground,  
with the thick bare wire from the breaker panel to Earth ground,  

and with a ground wire from where the neutral wire connects to the transformer  
and with a ground wire from where the neutral wire connects to the transformer  

also down to Earth ground. Why have this wiring all the way  
also down to Earth ground. Why have this wiring all the way  

to the Earth ground if it didn't play a part in our microwave oven fault?
to the Earth ground if it didn't play a part in our microwave oven fault?

To understand that, we need  to learn a bit about electric charge.
To understand that, we need  to learn a bit about electric charge.

Electric charge can be  either positive or negative.
Electric charge can be  either positive or negative.

Looking at an atom, the protons locked in  the atom's nucleus have a positive charge,
Looking at an atom, the protons locked in  the atom's nucleus have a positive charge,

and the electrons surrounding  the nucleus have a negative charge.
and the electrons surrounding  the nucleus have a negative charge.

Overall, this atom has a neutral  charge though, neither positive nor negative,
Overall, this atom has a neutral  charge though, neither positive nor negative,

because it has the same number of positive protons and negative electrons.
because it has the same number of positive protons and negative electrons.

Like charges repel each  other.
Like charges repel each  other.

Here we have an area with extra electrons between the atoms, so the area  
Here we have an area with extra electrons between the atoms, so the area  

is negatively charged overall. If we try to bring in yet  
is negatively charged overall. If we try to bring in yet  

another negative electron, it feels a repulsion, so it's harder to make it  
another negative electron, it feels a repulsion, so it's harder to make it  

go there. The like charges repel each other.
go there. The like charges repel each other.

But what if that area was the  size of the Earth? Or maybe just  
But what if that area was the  size of the Earth? Or maybe just  

your neighborhood? To negatively  charge such a large area would take  
your neighborhood? To negatively  charge such a large area would take  

a lot of extra electrons. Similarly,  we could positively charge the  
a lot of extra electrons. Similarly,  we could positively charge the  

area by taking electrons from it,  leaving more positive protons than  
area by taking electrons from it,  leaving more positive protons than  

negative electrons. But it doesn't  matter. The ground is such a large  
negative electrons. But it doesn't  matter. The ground is such a large  

volume that the ground normally  doesn't get very charged either way.  
volume that the ground normally  doesn't get very charged either way.  

It remains with a fairly neutral charge. So what's a good ground? A good ground is  
It remains with a fairly neutral charge. So what's a good ground? A good ground is  

one that has a large enough volume that can  
one that has a large enough volume that can  

handle whatever charge you're trying to give it, without it ever becoming very charged.
handle whatever charge you're trying to give it, without it ever becoming very charged.

Now, back to why we're connecting  wires all the way to Earth ground.
Now, back to why we're connecting  wires all the way to Earth ground.

One reason has to do with lightning.  Remember that the breaker panel  
One reason has to do with lightning.  Remember that the breaker panel  

case is connected to ground, and so  is the microwave oven's case.
case is connected to ground, and so  is the microwave oven's case.

When lightning stikes nearby, these cases  can become charged. By connecting
When lightning stikes nearby, these cases  can become charged. By connecting

to Earth ground, that charge bleeds  away to the ground,
to Earth ground, that charge bleeds  away to the ground,

keeping cases safe to touch.
keeping cases safe to touch.

Let's say the case becomes negatively  charged. As we said, like charges  
Let's say the case becomes negatively  charged. As we said, like charges  

repel each other. Since the ground  has a fairly neutral charge,  
repel each other. Since the ground  has a fairly neutral charge,  

the electrons on the case repel  along the wire to the Earth ground.  
the electrons on the case repel  along the wire to the Earth ground.  

And they keep repelling until there's  an even amount of charge everywhere.  
And they keep repelling until there's  an even amount of charge everywhere.  

Since the ground can take a lot of  charge, the overall charge doesn't  
Since the ground can take a lot of  charge, the overall charge doesn't  

even out until everything's fairly neutral. And yet another way to look at it is  
even out until everything's fairly neutral. And yet another way to look at it is  

that the negatively charged case has a certain quantity of charge and  
that the negatively charged case has a certain quantity of charge and  

the neutrally charged ground has a different quantity of charge.
the neutrally charged ground has a different quantity of charge.

That means they have different electric potentials. A potential difference,  
That means they have different electric potentials. A potential difference,  

or a voltage, exists between them. Since there's voltage between them,  
or a voltage, exists between them. Since there's voltage between them,  

if you connect them with a wire, current will flow.  
if you connect them with a wire, current will flow.  

Electrons will flow from the negatively charged case to the neutral ground. 
Electrons will flow from the negatively charged case to the neutral ground. 

For a ground rod to work well, the  ground does have to be electrically  
For a ground rod to work well, the  ground does have to be electrically  

conductive though, meaning  it has a low resistance.
conductive though, meaning  it has a low resistance.

Dry sand like this is not very conductive  and is a bad ground. But moist
Dry sand like this is not very conductive  and is a bad ground. But moist

soil is fairly conductive and is a better ground. Also, the more ground you connect to the  
soil is fairly conductive and is a better ground. Also, the more ground you connect to the  

better. Here I just pushed some wires into the ground,  
better. Here I just pushed some wires into the ground,  

and it wasn't very good. I even poured water in to help, but it still wasn't great.  
and it wasn't very good. I even poured water in to help, but it still wasn't great.  

You can buy copper and galvanized  steel ground rods that are around  
You can buy copper and galvanized  steel ground rods that are around  

6 to 10 feet long that you can  pound into the ground. But keep in  
6 to 10 feet long that you can  pound into the ground. But keep in  

mind that cold ground lowers the  conductivity, so make sure to  
mind that cold ground lowers the  conductivity, so make sure to  

drive it below the frost line for winter use. Besides the ground hole in a power socket,  
drive it below the frost line for winter use. Besides the ground hole in a power socket,  

where can you find a ground to use?
where can you find a ground to use?

If the current and voltage aren't  too high that you'd get hurt,  
If the current and voltage aren't  too high that you'd get hurt,  

then your own body can sometimes  act as an okay ground.
then your own body can sometimes  act as an okay ground.

An example where I've done that is with this  portable pizza box crystal radio.
An example where I've done that is with this  portable pizza box crystal radio.

It's portable because it doesn't  need a ground to work,
It's portable because it doesn't  need a ground to work,

but it works better with one. And  if you look closely here,
but it works better with one. And  if you look closely here,

you'll see my hand is on this  capacitor plate. The capacitor is  
you'll see my hand is on this  capacitor plate. The capacitor is  

one aluminum foil cylinder that  slides around another one, and with  
one aluminum foil cylinder that  slides around another one, and with  

paper in between. Making a lot of  skin contact with the outer cylinder  
paper in between. Making a lot of  skin contact with the outer cylinder  

lets it conduct charge to my hand  and body. Here, I'm the ground.
lets it conduct charge to my hand  and body. Here, I'm the ground.

Often when playing with high  voltage, you'll have a ball that's  
Often when playing with high  voltage, you'll have a ball that's  

connected to a wire going to ground  and make a spark by bringing that  
connected to a wire going to ground  and make a spark by bringing that  

near a charged object, like this  Van de Graaff generator.
near a charged object, like this  Van de Graaff generator.

A fairly safe way to ground that, if you don't  have a ground rod that you can
A fairly safe way to ground that, if you don't  have a ground rod that you can

connect to directly, is to find a metal pipe that you're certain goes  
connect to directly, is to find a metal pipe that you're certain goes  

into the ground, like this copper cold water intake pipe from the city.
into the ground, like this copper cold water intake pipe from the city.

Or this metal fence would do, since  it makes plenty of contact with the ground.
Or this metal fence would do, since  it makes plenty of contact with the ground.

And finally, what about this  
And finally, what about this  

ground symbol in the schematic for an electrical circuit?  
ground symbol in the schematic for an electrical circuit?  

Well, it's called a ground but very often it's more of a common reference.
Well, it's called a ground but very often it's more of a common reference.

For example, this schematic is for  this amplifier. Notice that it doesn't  
For example, this schematic is for  this amplifier. Notice that it doesn't  

contact any ground. In that case  it just means that all these  
contact any ground. In that case  it just means that all these  

points are connected together. For  the circuit board, I soldered all  
points are connected together. For  the circuit board, I soldered all  

those points to a bare wire in the  back. Anything connected to that common  
those points to a bare wire in the  back. Anything connected to that common  

reference will have voltages that  are relative to that common,
reference will have voltages that  are relative to that common,

a sort of zero for the voltage. There are other ground symbols too.  
a sort of zero for the voltage. There are other ground symbols too.  

This one means chassis ground, such as the chassis of a car,  
This one means chassis ground, such as the chassis of a car,  

basically a continuous piece of metal that many things in the car are connected to,  
basically a continuous piece of metal that many things in the car are connected to,  

including battery negative. Sometimes though, the ground symbol  
including battery negative. Sometimes though, the ground symbol  

does actually refer to connecting to Earth ground object. This is the schematic
does actually refer to connecting to Earth ground object. This is the schematic

for this power supply, one that you plug into a wall with  
for this power supply, one that you plug into a wall with  

a plug that has a ground prong. In this case, the symbol is saying  
a plug that has a ground prong. In this case, the symbol is saying  

to connect to that ground prong, though I guess your only hint is  
to connect to that ground prong, though I guess your only hint is  

that these points are labeled as hot and neutral, the names for  
that these points are labeled as hot and neutral, the names for  

the other two prongs in the plug. Well, thanks for watching!
the other two prongs in the plug. Well, thanks for watching!

See my youtube channel for more  informative videos like this.  
See my youtube channel for more  informative videos like this.  

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