Describe the electrical safety features in the home, including fuses, earthing and insulation, and explain safe practices to avoid electric shock

What this dot point is asking

This dot point wants you to describe the safety features that protect us from mains electricity in the home, such as fuses, earthing and insulation, and to explain safe habits that prevent electric shock. The big idea is that mains electricity is useful but dangerous, because the large current and high voltage can cause electric shocks and fires. Several built-in safety features and a few sensible habits keep us safe.

The answer

Why mains electricity is dangerous

The electricity in the home (the mains) has a much higher voltage and can supply a much larger current than a small battery. If this current flows through a person, it can cause a serious electric shock, which can injure or even kill. If wires or appliances overheat, they can also start a fire. This is why safety features and safe habits matter.

Insulation

Insulation is a covering of material that does not let electricity through. The wires inside cables and plugs are covered in plastic, which is a good insulator.

The plastic stops the current escaping and stops you touching the bare, live metal wire inside. If insulation becomes worn or frayed so that bare wire shows, it is dangerous and the cable must be replaced. Many appliances also have a plastic case for the same reason.

Fuses

A fuse is a safety device that contains a thin piece of wire. It is fitted in the plug or the fuse box.

If too much current flows, for example because of a fault, the thin wire in the fuse gets hot and melts (blows). This breaks the circuit and cuts off the current before the cable or appliance can overheat and catch fire. A blown fuse must be replaced with the correct type, never with a thicker wire. A circuit breaker does a similar job and can simply be switched back on.

Earthing

Earthing is a safety feature for appliances with a metal case. A third wire, the earth wire, connects the metal case to the ground (the earth).

Normally no current flows in the earth wire. But if a fault makes the metal case "live" (connected to the live wire), the current flows safely to earth through the low-resistance earth wire instead of through a person who touches it. This large current also blows the fuse, switching the appliance off. So earthing protects you from a shock from a faulty metal appliance.

Safe practices

Safe habits matter as much as the built-in features:

• Do not use electrical appliances with wet hands or near water, because water lets electricity flow through it and through you.
• Do not overload a socket with too many plugs, as this can overheat and cause a fire.
• Switch off at the socket before unplugging, and never pull a plug out by the cable.
• Do not use appliances with damaged cables or cracked plugs; get them repaired.

Examples in context

Example 1. A plug for a metal lamp. Open a plug for a metal-bodied lamp and you find three wires going to three pins, plus a small fuse. The plastic around each wire is insulation, the fuse will blow if a fault sends too much current, and the earth wire connects the metal body to the ground. All three safety features sit inside one small plug.

Example 2. Hairdryers and the bathroom. Warnings tell you never to use a hairdryer near a filled sink or in the bath, because water conducts electricity. If a wet hairdryer became live, the water could carry the current through your body, giving a severe shock. This is why bathrooms have special safety rules for electricity.

Try this

• Cue. State what a fuse does when too much current flows, and why this is useful. The thin wire in the fuse melts (blows) and breaks the circuit, cutting off the current before the cable overheats and causes a fire.

• Cue. Explain why the metal case of an appliance is connected to an earth wire. So that if a fault makes the case live, the current flows safely to earth instead of through a person, and the large current blows the fuse.

• Cue. Give two safe practices when using electricity at home. For example: do not use appliances with wet hands or near water, and do not overload a socket with too many plugs. (Accept other sensible answers.)