This document provides information about electrical energy and dangers of electricity. It discusses types of dangers like overheating cables, damp environments, and damaged insulation. It then describes various safety features used at home like circuit breakers, fuses, switches, earthing, three-pin plugs, and double insulation. Circuit breakers and fuses prevent excessive current flow by tripping or blowing. Switches should be connected to live wires. Earthing provides a path for stray currents. Three-pin plugs contain a fuse. Double insulation insulates internal components from external casing. An example calculation for a suitable fuse rating to protect an iron is also provided.

1. Recap!
Electrical Energy

2. Example 1
A 24 ohm resistor is to be connected in series
with a 12V battery. What is the power loss in
the resistor?
Hint : Solve using V=IR & P=IV

3. Example 2
A Lamp has a power rating of 100w and was
used for 5 hrs. A cooker has a power rating of
3kW and was used of 0.5 hrs. What was the
cost for the total usage of both the appliances
if the cost of a unit (kWH) of electricity is
$0.10?

4. Practical
Electricity
Dangers of Electricity

5. Types of Dangers
Overheating of Cables Damp Environments Damaged Insulation
• Overloaded power
sockets cause
large current flow
• Use of
inappropriate wires
may result in
overheating
• Insulating materials
can become worn
with time exposing
the conducting wires.
• Conducting wires can
cause shocks if
touched
• Water is a good
conductor of
electricity and it
can act as a
conducting path
for currents if in
contact with
uninsulated parts
of electrical wires

6. Safety Features at Home
• Circuit Breakers
• Fuses
• Switches
• Earthing
• Three-pin Plugs
• Double Insulation

7. Circuit Breakers
•
circuit when a current that flows
through them is too large
• Live wires are connected to circuit
breakers to ensure that the circuit
breaker will trip andcut off supply
to the appliance
Switch off electrical supply in a

8. Switches
•
• Switches should to connected to
live wires to prevent electric
shock in case of electrical faults

9. • Live Wire (Brown) is connected
to high voltage & delivers current
• Neutral Wire (Blue) completes the
circuit by providing a return path to
the supply for the current
• Earth Wire (Green & Yellow) is of
low resistance so that current can
Earthing

10. Earthing

11. Fuses
• Acts similarly to circuit breakers,
preventing excessive current
flow
• However, instead of tripping,
fuses blow and have to replaced
once the blow
• Fuses have a thin wire, which
overheats and melts creating an
open circuit.
All fuses come with a
rating which indicates
maximum current that is
allowed to flow through
before the fuse blows

12. Calculation involving
Fuses
Example Qn
A iron is rated at 1740W & 240V. What would be the current
required for the iron to operate? What would be a
suitable fuse rating to protect the iron from overheating?
Using P=VI, I= P/V = 1740/240 = 7.25A
Therefore, a fuse slightly larger than the current flowing

13. Three-Pin Plug
• Fuse protects the appliance
when there is an electrical
fault
• When excessive current
flows through, the fuse
blows, breaking the circuit
so that it does not overheat
the appliance and damage it

14. Double Insulation
• Electric cables are
insulated from the internal
components
• Internal components are
insulated from external
casing
• Usually cased in non-metallic
materials

15. Homework!