Safety of Electricity Slides Grade 9, South Africa

1. ELECTRICITY SAFETY
MISS. GM GEDDES
SEPTEMBER 2015
VICTORY HOUSE
bit.ly/1cO4vmZ

2. RECAP
Is a house connected in parallel or series…. WHY??
The disadvantage to having a house
connected in parallel is that it can
become OVERLOADED, this can cause a
FIRE , which can BURN DOWN YOUR
HOUSE

3. ELECTRICITY SAFETY TIPS

4. OUTCOMES FOR THIS LESSON
• Draw a circuit in parallel or series containing a fuse
• Explain why certain household appliances need to be earthed
• Discuss how a house is wired
• Distinguish between the different connections found in a plug
• Relate the use of electricity to a South African context
• Name the negative effects of illegal connections
• Differentiate between a fuse and a circuit breaker

5. EARTHING
• The only time it is used is when something goes wrong inside the machine.
• If the live wire is exposed and touches the metal casing of the washing
machine, you could get an electric shock if you then touch the metal casing.
• However, the earth wire is connected to the metal casing so that the current
goes through the earth wire and into the ground instead of shocking you.
• The earth wire has a very low resistance and so a strong current will easily
go through it.

6. EXAMPLE OF EARTHING

7. WHAT DOES AN EARTH WIRE DO?
• The earth wire completes the circuit and connects the live wire
to the ground.
• This is a short circuit. The washing machine will stop working
because none of
• the electricity will flow through the motor.

8. WHAT WOULD HAPPEN IF THERE WAS
EARTH CABLE?
• If there was no earth wire then the metal casing of the washing
machine would become part of the electrical circuit and anyone
who touched it would get an electrical shock.
• That is why an earth wire is an important safety feature on any
electrical appliance.

9. THIS IS HOW IT LOOKS
INSIDE A WASHING
MACHINE:

10. SHORT CIRCUIT
An extra electrical pathway is made.
The extra electrical pathway has very low resistance and so the
current increases.
This increased current can damage appliances and cause
overheating.

11. WHAT IS A FUSE
• A fuse is a wire which will melt if the current
travelling through becomes too
• large due to a fault, GIVE AN EXAMPLE: SHORT
CIRCUIT, OVERLOAD
• Thus the circuit is broken and no current can flow,
• The photo is of a 5 ampere fuse. It will if a current
of more than 5 amperes passes through it.
• Circuit breakers are more commonly used in
households.

12. CIRCUIT BREAKER
• A circuit breaker is similar to a fuse except that it can be reset.
• Basically a switch that “trips”

13. HOW DOES A CIRCUIT BREAKER WORK?
1. When the switch is on, the current flows through the device, from the left
through the moving contact and across to the stationary contact.
2. It then goes
around the electromagnet and out the other side.
3.The iron catch is holding the
moving contact in place so that the circuit is complete.

14. • 4.If the current passing
• through the circuit breaker increases, the electromagnet becomes stronger.
• 5.If the current gets to unsafe levels, the electromagnet becomes strong enough to
• pull the iron catch lever.
• 6.This releases the moving contact so that the circuit
• breaks and the electricity is shut off, as shown in the following diagram.

15. DISADVANTAGE ADVANTAGE
FUSE Has to be replaced Cheap, easily available
CIRCUIT BREAKERS Expensive Can just be turned on again

17. EARTH LEAKAGE -type of circuit breaker
• Used in households and businesses
• It works for different areas in the house / business
• The breakers are found on the distribution board

18. WHAT DOES AN EARTH BREAKER DO?
• The earth leakage circuit breaker is a safety device which can switch off the
electricity supply to the house.
• The earth leakage is able to detect if any current is moving through the
earth wire.
• If current is moving through the earth wire then there is a short circuit
somewhere,
• for example as explained with the washing machine.
• The earth leakage circuit breaker then shuts down all the current as a safety
measure.

19. LIGHTNING
• Can be a danger to an electric circuit
• Lightning spikes or conductors
are used often

20. WHEN LIGHTNING STRIKES…
• The surge of current will flow through the rod and safely into
the ground. This will help prevent fires in households

21. HOW TO SURVIVE LIGHTNING

22. WIRING A 3- PIN PLUG
• • a brown live wire
• • a blue neutral wire
• • a green and yellow
striped earth wire
The wire which enters our
homes is the live wire. The neutral wire
leaves our homes and is earthed as it
leaves the house. The earth wire has a
very low resistance and is connected
through the plug socket to the earth
cable of the house. The earth cable
leads into the ground.

23. • BRUIN REGS (power into house) Live
• BLOU LINKS (power out of house) Neutral
• GROEN EN GEEL BO (earth the house)

25. ILLEGAL CONNECTIONS
An illegal electricity connection is
made when a person attaches their
home's
electrical circuit to the national grid
without a meter. This is done without
the
consent or knowledge of Eskom.
Eskom cannot monitor the electricity
consumption and so the electricity is
being stolen as these consumers do
not pay for the electricity.

26. ILLEGAL CONNECTIONS
• Some people make money by
supplying illegal connections and others
have no legal way to access
electricity and so they resort to illegal connections.
Others have access to legal electricity,
but prefer not to have
to pay for it. Not only are these types
of electrical connections illegal and
considered energy theft, they are also
very dangerous,

27. EFFECTS OF ELECTRICITY THEFT
• Stability and quality is influenced
• Can lead to power interruptions
• Eskom cannot keep up with the increasing demand to provide
electricity
• Big financial losses
• People and animals can be shocked to death or get seriously
hurt.

28. SUMMARY
• Electricity can be dangerous and so we need safety devices such as fuses,
circuit breakers and earth leakages to reduce risk.
• A fuse is a safety device with a very low resistance wire, designed to melt if it
experiences a large enough current. This breaks the circuit and protects the
appliance, as well as preventing a possible fire hazard.
• A circuit breaker is like a fuse, but acts as a switch which breaks the circuit in
response to an electrical fault or overload. It can be reset.
• Many electrical appliances with a metal casing have an earth wire attached to
prevent electric shocks if there is a short circuit.

29. SUMMARY
• A three-pin plug has three wires: a brown live wire, a blue neutral wire and a
green and yellow striped earth wire.
• The earth wire has a very low resistance and is connected through the plug
socket to the earth leakage system of the house, and into the ground.
• A plug must be connected properly in order to make sure that it is safe to use.
• Illegal electricity connections are both dangerous and illegal. It is a crime to
steal electricity.

30. THE ELECTRICITY SONG