Hey there guys. Paul here from TheEngineeringMindset.com. In this video, we're going to
be looking at the difference between the hot, neutral and ground wires as well as the function of
each with some worked examples. This video is for homes in North America. If you are outside this region then you can still follow along
but your system will work and look a bit different, so
do check out our other videos. Remember, electricity is
dangerous and can be fatal. You should be qualified and competent to carry out any electrical work. Before we get into this video, there are three things
I need you to remember. Number one, electricity will only flow in a complete circuit. If you come into contact
with an electrical conductor, your body might complete the circuit. Number two is that
electricity always tries to return to its source and number three, electricity will take all available paths to complete a circuit but
it will take preference to a path with less
resistance and so more current is going to flow in that path. So we're going to be looking at the hot, neutral and ground wires for a typical North American
residential electrical circuit. First we'll see a really simple circuit to understand how it works, then we're going to apply this knowledge to a complex residential installation. When we look at a simple
electrical circuit with just a battery and a lamp, we know that to turn the lamp on we need to connect both ends of the wires to the terminals of the battery. Once we connect these wires, the circuit is now complete
and electrons can flow from the negative through the lamp and then back to the positive terminal. So for the circuit to be complete, we need a wire to carry the
electrons from the power supply and over to the light. This wire is our hot wire, then we need to connect
another wire from the lamp and back to the battery for the electrons to get back to their power
supply or from their source, and this wire is our neutral wire. The hot wire carries electricity
from the power supply and then will take this over to the load. The neutral wire carries
the used electricity back to the power supply. If we look at a residential
electrical system in North America, then we
will find two hot wires a neutral wire and some ground wires. If you want to see in
detail how this all works then check out our video for that, links in the video description below. Now, imagine for a second,
the homes electrical system is connected to a battery
and we have just one hot wire and a neutral wire. And as we saw with the simple circuit, for the light to turn
on, we need a hot wire to the supply of the current to the load and we need the neutral wire to return the current to the source. Electricity therefore
flows through the hot, through the busbar and the circuit breaker
and into the light. It then travels back through the neutral and over to its electrical source. Now, of course homes are
not connected to a battery, they are connected to transformers. So we're gonna replace the
battery with a transformer and there we go, we
have a complete circuit. The electricity in this circuit
is AC, alternating current, which is different from
the DC, direct current, which we saw with the battery. With DC, the electrons flow directly from A to B in only one direction, much like the flow of water down a river, but in our homes we have
AC, alternating current, which means the electrons
alternate their direction between forwards and backwards much like the tide of the sea. Now, in North America, we
have a split phase supply to most residential properties. So we have the two hot
wires and one neutral wire. We simply have two 120V coils
which are connected together in the transformer. The neutral is then
connected to the centre between the two coils. When we connect our multimeter between a hot and the neutral, then we're going to get
a reading of around 120V, and we get the same
reading for the other one. That's because we're only
using half of the coil in the transformer. But then when we connect
between the two hots, we get 240V because we're
using the full length of the transformer coil. Now, if you don't have a multimeter, I highly encourage you to get one, links down below for which
one to get and from where. Now, if we have a load on
only one half of the coil and the load is, for example, 20Amps, then the hot wire will
carry 20Amps to the load and the neutral wire will carry
20Amps back to the source. You can measure the current in a cable using a current clamp meter. Again, links down below for
which one to get and from where. If you don't know what
current or amps are, then check out our video
on electrical current, link to that in the video
description below also. Now, if we have another load
on our other half of the coil and the load is a different value, say for example just 15Amps,then
the neutral will only carry the difference between
these two values back to the transformer or back
to the electrical source. So in this case, one side we have 20Amps and the other side we have 15Amps, so the difference between
these is five amps. So the neutral will carry five amps. Where does the rest of this go? Well, it will pass
through the two hot wires. And this is what we have in most cases because there are multiple
circuits with different loads in the residential property. However, if we had a load on both coils and they're of equal value,
say for example 15Amps each. Then there will be no current
flowing in the neutral wire. So where is it going? Well, it's flowing back and
forth on the two hot wires between the load and the source. That's because it's AC,
alternating current, and the transformer is
centre tapped with a neutral. So while one half is moving forwards, the other half is moving backwards and the current will flow
into the other circuit instead of back via the neutral. Hopefully, that hasn't
confused you too much. If it has, then don't worry
about it too much for now, we're gonna cover that
in a more advanced video. So the hot wires carry
the electrical current from the supply and over to the load and the neutral wires carry
the electrical current from the load and back to the supply. So what does the ground wire do? The ground wire, under
normal operating conditions, will not carry any electrical current. This wire will only
carry electrical current in the event of a ground fault. Hopefully, this wire will
otherwise never ever be used at all in its entire life. It's just there for an emergency path for the electricity to get
back to the power source instead of it passing through you. The ground wire in most
cases is a bare copper wire, it's uninsulated, but in
some cases it is covered with a green insulation. This wire has a very very low resistance so electricity will
prefer to travel along it because it's easier and
can get back quicker. Now if we go back to the simple circuit with a battery and a lamp,
if we now run another wire and run this from the positive
terminal over to the lamp and we connect this to the
metal of the lamp holder, then this is effectively our ground wire. As you can see, it's not being
used to carry electricity. If the hot wire touches the metal casing then the electricity will now flow through the ground wire instead. If the hot wire is connected
to both the neutral and the ground, then it will now flow through both wires back to the source. But as the ground wire
has less resistance, then more current will flow through it. When electricity finds a
way to leave its circuit and return to the source
through a different way than its neutral wire, this
is called a ground fault. Coming back to the house, the electricity flows through the hot wire and into the light and then
back through the neutral, but if the hot touches the metal casing, then it will instead flow
through the ground wire back to the panel, through the busbar and then back to the transformer
via the neutral wire. The ground wire has a very low resistance which causes a huge and
instantaneous increase in current which will trip the breaker. We therefore connect the
ground wires to anything that could potentially
become a potential path for electricity to leave its circuit, such as the metal pipes, the metal plates and the light switches and
the outlets of the boxes, we also need to run one to the outlets because often our
appliances are made of metal or they're covered with a metal casing, the things like washing
machines and microwaves. When you look at a receptacle and plug, you'll see that there is a hot terminal, a neutral terminal and a ground terminal. The casing of something
like a washing machine is connected to a ground wire in the lead which goes to the plug,
through the receptacle and back to the panel to save
you from an electric shock. Now, let's say you're
outside with no shoes on and the ground or the soil is moist. If you touch a hot wire, you
could complete the circuit and current may pass through
you to get back to the supply. In this case, the resistance
is going to be very high. So the current might not be high enough to automatically flip the
breaker and cut the power. This will likely lead
to the person's death. Luckily we have the GFCI
receptacle or the GFCI breaker. GFCI stands for Ground
Fault Circuit Interrupter. We're gonna look at a
circuit breaker version but essentially they're
gonna work the same. This GFCI breaker is going to be connected to both the hot and the
neutral of the circuit, and so we can monitor the wires and ensure that the current running in
the hot wire of the circuit is equal to the current running in the neutral wire of the circuit. If the current is not
equal in these two wires, then it's clearly flowing
back to the source via another route, we
then have a ground fault. The breaker will realize
this and very quickly and automatically flip to cut the power and kill the circuit. Connected to the main panel, we will find a thick copper wire which leads out to a ground rod. A ground rod is buried into the ground outside near the property. This rod is not used for ground faults. Its purpose is to dissipate
static electricity and external high voltages
like lightning strikes. There is also a ground rod
connected to the neutral at the transformer. Many people think that
during a ground fault electricity flows through the ground rod and into the earth. Now, remember electricity tries
to get back to its source. It doesn't just go into the earth. Unless there is a ground
rod at the transformer, then there is a potential
path for the electricity to get back to the source,
but this path will have a very high resistance for impedance. And as we know, electricity
will take preference over the path with the least resistance. So as we already have a very
low resistance ground wire which provides a path
directly back to the source, the ground fault is going
to take this route instead. When it comes to lightning, the source of lightning
is essentially the earth. So lightning is always trying
to get back to its source which is the earth. If lightning strikes the utility cables, it will flow along the wires
to get to the ground rods of both the transformer
and also your main panel. It's gonna do this to try
and get back into the earth. If it wasn't for this,
then it's going to blow all our circuits then it's
gonna cause house fires. Now, if the hot wire
came into direct contact with the ground rod, then
electricity will flow through the soil, back to the transformer, but the resistance is very high
so the current will be low. This means the circuit breaker will not likely detect the fault and the circuit breaker
will not automatically flip to cut the power. Okay guys, that's it for this video but to continue learning, then click on one of
the videos onscreen now and I'll catch you there
for the next lesson. Don't forget to follow us on
Facebook, Twitter, Instagram, as well as TheEngineeringMindset.com.
