Circuit breakers

Starter Task

Q1 Which two mains wires carry the current if a device is working normally?

Q2 Where should the Earth wire be connected?

Q3 If the body of an appliance becomes live, what job does the Earth wire do?

Q4 What would happen if the Earth wire were not connected and someone touched the

appliance?

Q5 What sort of appliances do not need an Earth wire?

A current flowing in a coil of wire creates a magnetic field. Circuit breakers use this field to detect the size of the current

…and now…

…the Magnetic Circuit Breaker (MCB)…

…which makes use of the magnetic effects of large currents…

The RCD (residual current device)

Q1 What is created around a coil with an electric current flowing in it?

Q2 What happens to the strength of the field if the current gets bigger?

Q3 How does the MCB use a magnetic field?

Q4 When should the MCB be used?

Q5 How does the RCD use a magnetic field?

Q6 When should the RCD be used?