Download Home Electric Wiring

HOME ELECTRIC WIRING
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HOME ELECTRIC WIRING

Most Homes in Ontario are connected to a
Power Transmission Grid. The grid is a huge
circuit. It covers hundreds of kilometres. The grid
connects each building to a power source. The
power station is the source of electric energy.

Electric wires carry current to each building
through a central electric panel. A number of
separate circuits carry current from the central
electric panel to different parts of the home. The
arrangement of circuits in a building is often
called the wiring.

Each circuit in the house is designed to handle a
certain number of loads safely. Special circuits
may also be designed for certain kinds of loads.
Only qualified electricians should ever try to
change wiring in a home.
Question: Think about the series and parallel
circuits you have built
 What will happen in your home if you connect too
many electrical devices in parallel in the same
circuit?

The circuit breaker will cut off power to avoid the
chance of a fire.
KNOW YOUR VOLTAGE

In North America, most household electric
circuits carry 120 V. However, different electrical
devices operate at different voltages
120 V
A regular
household electric
current is connected
to a 120 V circuit
Some household outlets
are connected to a
240V circuit.

It is very important to make sure each device is
plugged in at its correct voltage. If the voltage is
too low, the device will not work. If the voltage
is too high, the device will be damaged. The
circuit inside the device may even explode. This
can hurt people or start a fire.

Some Large appliances work at 240 V. Electric
stoves, freezers, and clothes dryers are examples
of appliances that may need 240 V. These
appliances have special outlets. A regular electric
plug will not fit into a 240 V outlet.

Many devices operate at less than 120 V. A
device that operates at 12 V cannot be plugged
directly into a regular 120 V outlet. Instead, the
plug carries current through a transformer. The
transformer reduces the voltage to 12 V.
QUESTION

When will an electric device require a
transformer?


When the voltage is too high
Why are 240 V outlets shaped differently from
120 V outlets?

To prevent 120 v appliances from being damaged
KNOW YOUR CURRENT

Every electrical device needs a certain amount of
electric current. Different kinds of devices use, or
draw, different amounts of current. Appliances
that convert electricity to heat usually draw more
current than other kinds of appliances.

Remember, when loads are added in parallel, the
total current in the circuit increases. The same
thing happens when you connect more devices to
an electric circuit by adding up the current draw
by each device.

Example: An electric kettle draws about 8 A. A
clock radio draws about 1 A. If you connect both
of these appliances in one parallel circuit, the
total current in the circuit is 8 A + 1 A = 9 A.
Kettle 8 A
Clock radio 1 A

An electrician planning a home electric system
must think about what kinds of appliances will
be used in the home. The electrician must also
think about where these appliances will be used.
Each circuit must be designed to carry the right
amount of current for its intended use.

What is the total current in this circuit?
3A

3A + 3A + 3A + 3A = 12 A
3A
3A
3A
DRAW A CIRCUIT FOR EACH SITUATION.

Draw an A.C. power source with one 3A bulb in
parallel with one 6 A bulb.


What is the total current draw in the circuit?
DRAW A CIRCUIT FOR EACH SITUATION.

Draw an A.C. power source with one 3A bulb in
parallel with one 4A bulb and one 5A bulb.


What is the total current draw in the circuit?
Fuses and Circuit
Breakers
Fuses and Circuit Breakers
• Each circuit in a home is designed to carry
a certain maximum current. A 15 A circuit
can carry up to a maximum of 15A of
current. If the current is less than 15 A, the
circuit is safe.
• IF the current rises above 15 A, the circuit
is overloaded.
• A circuit can become overloaded when too
many devices are connected in parallel. A
short circuit can also cause a circuit to
overload.
• An overloaded circuit can be dangerous.
The conducting wires can heat up and start
a fire. To make sure this does not happen,
each circuit in a home is protected by either
a fuse or a circuit breaker.
• Fuses and circuit breakers are important
electric safety devices. They are designed
to stop current from flowing in an
overloaded circuit until the problem is fixed.
• For the following two examples, write “safe”
if the circuit is safe. Write “overloaded” if
the circuit is overloaded. Show how you
know.
• A)
• Safe
3A
3A
• 3 + 3 + 2 + 2 = 10 A
2A
2A
• B) 15 A
• overloaded
• 2 + 3 + 3 + 3 + 6 = 17
2A
3A
3A
3A
6A
How a Fuse Works
• What is the circuit symbol for a fuse?
• A fuse prevents too much current from
flowing through a circuit. If the current is too
high, the wire conductor inside the fuse
melts. This opens the circuit. No electrical
device on the circuit will work until the fuse
has been replaced.
15 A
• An intact fuse. Current flows through the
wire inside the fuse. The circuit is closed.
• A “blown” fuse. The wire has melted.
Current does note flow through the wire.
The circuit is open.
• Many homes have a fuse box. The fuse
box holds all the fuses for all the circuits in
the house or apartment.
• The fuse box is connected to the central
electric panel.
• If you are replacing a fuse, always make
sure that new fuse is exactly the right kind.
If a new fuse blows right away, do not
replace it again. Have an electrician check
the circuit. There may be a problem in the
electric system.
• Why could it be dangerous to put the wrong
kind of fuse in a circuit?
• It could allow too much current through
which could damage things or lead to a fire.
• Fuse boxes are not just in homes. Cars,
trucks, motorcycles, stereo equipment and
various other devices all have fuse boxes in
them to protect their electrical equipment.
• An electric circuit connects three bulbs in
parallel. Each bulb draws 3 A. One 10 A
fuse protects the circuit.
– Draw a diagram of the circuit
– Explain what happens when a space heater
that draws 12 A is connected to the circuit.
• The fuse will blow
10 A
12 A
3A
3A
3A
How a circuit breaker works
• A circuit breaker is designed to cut off
electric current in an overloaded circuit just
like a fuse does. A circuit breaker works
like switch. If the circuit is overloaded, the
circuit breaker trips. This opens the circuit.
After the problem has been fixed, the circuit
breaker can be reset to close the circuit.
• What is the symbol of a circuit breaker?
• One advantage of a circuit
breaker is that it can be
used over and over again.
Many newer kinds of circuit
breakers also open an
overloaded circuit faster
than a fuse can. For these
reasons, all newer
buildings use circuit
breakers instead of fuses.
• A circuit panel has a circuit breaker for
each circuit in the building. The directory on
the door of the panel describes what
appliances or electric outlets are connected
to each circuit.
• The directory also tells you how much
current each circuit can carry safely.
• For the following drawings, add up the
current that each appliance uses to see if it
will blow or trip the circuit.