1. Mains Plug Wiring:
Brown lead
Live
Blue Lead
Neutral
Green and Yellow Lead
Earth
Safety Features: a) the fuse (“blows”) with current overload

2. Safety Features of the mains plug
the fuse
“blows” with current overload
The earth wire
Provides a safe electrical path from the metal case of an appliance
The cable grip
prevents “mechanical” damage to the electrical components.
The moulded plastic case
Insulates the connections and firmly separates cables from each other

3. Electrical Cable consists of three “double insulated” copper leads.
This insulation is provided by the OUTER cable made of PVC and the inner plastic “SLEAVES” which are colour coded. The cable itself is made of copper wire which is flexible and has very low resistance.
As we will see the most dangerous wire is the brown “Live Wire”
The neutral wire is essential to complete the circuit.
The earth wire is a safety device which does not carry a current in normal circumstances
LIVE WIRE
NEUTRAL WIRE
EARTH WIRE

4. The mains a.c. circuit

5. The mains a.c. circuit

6. The mains a.c. circuit

7. The mains a.c. circuit
The electric current is pushed back and forth 50 times per second. So the p.d has to change 50 times a second
This is done by keeping the neutral lead at 0V and changing the potential applied to the LIVE Wire smoothly from a high positive potential to a high negative potential.
The potential difference averages out at 230V

8. LIVE WIRE
+300V
p.d./V
Time/s
-300V
p.d./V
Time/s
NEUTRAL WIRE

10. Any Appliance With a METAL Case Must Be Earthed
Earth connection
Metal Case

11. Case at 230V
Metal Case
Without Earth Connection
Frayed Wire
Without an earth connection there will be a high potential difference between the case and earth.
The current can move to earth though a person who touches the case
Earth at 0V

12. Frayed Wire
Metal Case
The large current flowing from live to earth now blows the fuse in the mains plug
As soon as the case becomes live current follows the easy route to the ground provided by the earth lead.
Large conductor buried in the ground

13. The Earth Lead
This is an earth lead attached to a large copper pipe buried in the ground. Many old electric showers were earthed this way.
It is not allowed now because plumbers have started to use plastic pipes.