19.1 - Mains Wiring & Safety
Why the live wire is dangerous
- Your body, like the earth, is at about 0 V. The live wire is at about 230 V.
- Touching the live wire makes your body a link between the supply and the earth, creating a large potential difference across you.
- This drives a current through your body, causing an electric shock that can injure or kill.
The danger stays when switched off
- Even with an appliance switched off, the live wire before the switch is still at 230 V.
- Touching it would still complete a circuit to earth, causing a shock.
Live-to-earth connections
Any connection between the live wire and earth is dangerous. If that connection is a low-resistance path, a very large current flows, which can start a fire.
Hazards of mains electricity
- Damaged insulation - Exposes the live wire. Touching it can drive a current through your body, giving an electric shock.
- Overheating cables - Drawing too much current through a cable that is too thin causes it to overheat and can start a fire.
- Damp conditions - Water conducts electricity, which can create a conducting path outside the wires and cause a shock.
- Overloading sockets - Plugging too many appliances into one socket draws an excessive current that can overheat the wiring and cause a fire.