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