Electrical safety Flashcards – Cambridge IGCSE (9–1) Physics 0972 (Extended) (2026–2028)

What hazards can damaged cable insulation create?

It can expose live conductors, risking electric shock if touched, and cause short circuits and fire.

What can happen when a cable overheats?

Its insulation can be damaged, and a fire can start.

Why do damp conditions increase the risk of electric shock?

Water containing dissolved substances can conduct current, providing a path through a person.

Why can overloading a plug, extension lead or socket cause a fire?

Appliances drawing too much total current can overheat cables and connections.

What are the three wires in a mains circuit?

The live (or line), neutral and earth wires.

What potential does the live wire carry relative to earth?

An alternating potential.

What is the role of the neutral wire during normal operation?

It provides the return path for current.

What is the role of the earth wire in a mains circuit?

It is a safety connection and normally carries no current.

Where must an appliance switch be connected, and what does opening it disconnect?

In the live wire; opening it disconnects the appliance from the live supply.

Why is switching only the neutral wire hazardous?

Parts of the appliance can remain connected to the live wire, creating an electric shock hazard.

How does a fuse stop excessive current?

Current heats the fuse wire. If the current is excessive for long enough, the wire melts, breaking the circuit.

What must be done before a circuit can operate again after its fuse has blown?

The blown fuse must be replaced.

What makes a fuse rating suitable for an appliance?

It is above the appliance’s normal operating current but low enough to protect the circuit and cabling from excessive current.

How can an appliance’s normal current be calculated from its power and supply voltage?

$I = \frac{P}{V}$

Does a fuse need an earth connection to protect the circuit and cabling of a double-insulated appliance?

No. It operates when excessive current flows without an earth connection.

What does a trip switch do when the current exceeds its set value?

It automatically opens the circuit, interrupting the current and reducing the risk of overheating and fire.

When can a trip switch be reset after it operates?

After the cause of the excessive current has been dealt with.

What must a trip switch setting allow and protect against?

It must allow the normal operating current while protecting the circuit and cabling from excessive current.

How can normal operating current be calculated from power and supply voltage when selecting a trip switch setting?

$I = \frac{P}{V}$

How does double insulation protect an appliance’s accessible surfaces?

Non-conducting insulation separates accessible surfaces from live electrical parts.

Does a double-insulated appliance require an earth wire?

No.

How does earthing a conducting appliance casing protect against electric shock if the live wire touches it?

The earth connection provides a low-resistance path for a large fault current. A suitable fuse or trip switch then disconnects the supply.