Mains Safety
The electricity in your walls is 230 volts of alternating current — enough to kill. Learn a.c. from d.c., wire a plug correctly, and understand why the live wire is deadly even when the switch is off.
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Mains Safety ⚡
The electricity from a battery and the electricity in your wall sockets are not the same thing. One is gentle and one-directional; the other reverses 50 times a second and can kill you. Understanding the difference — and how a plug is wired — is what keeps you safe.
Two kinds of current 🔄
**Direct current (d.c.)** always flows in **one direction**. Cells and batteries supply d.c. **Alternating current (a.c.)** **periodically reverses direction**, flowing one way then the other over and over. The **mains supply is a.c.**, produced by generators.
Spot the mains supply
Which statement correctly describes the electricity from a UK mains socket?
- Alternating current, which periodically reverses direction
- Direct current, always flowing in one direction
- A current that never changes and never flows
- Both a.c. and d.c. at the same time
The UK mains 🏠
UK mains electricity is supplied at about **230 volts** and a frequency of **50 hertz (Hz)** — meaning the alternating current completes 50 full cycles every second. It reaches appliances through a **three-core cable**: three separate wires, each with its own job and colour.
Three wires, three jobs 🎨
Inside the cable: • **Live** — **brown** — carries the alternating potential difference from the supply. • **Neutral** — **blue** — completes the circuit and stays near **0 V**. • **Earth** — **green and yellow** — a **safety** wire that carries current **only if there is a fault**.
Wire the plug correctly
An interactive activity.
Match each wire to its exact job
- Live wire (brown)
- Neutral wire (blue)
- Earth wire (green & yellow)
- Carries the alternating potential difference from the supply
- Completes the circuit and sits near 0 volts
- A safety wire that carries current only if a fault occurs
The hidden danger
Why is the live wire dangerous to touch even when the appliance is switched OFF?
- It is still at about 230 V relative to earth, so touching it makes a large p.d. across you and gives a shock
- It permanently stores charge like a fully charged battery
- It only carries current when there is a fault
- It is at 0 V, so it slowly heats your hand
What does earth do?
In normal use, what does the earth wire do?
- Almost nothing — it is a safety wire that only carries current if a fault occurs
- It carries the main working current to the appliance
- It completes the circuit at 0 V during normal use
- It converts the a.c. supply into d.c.
Safety summary
Mains electricity is _____ current at about 230 V and 50 Hz. In a three-core cable the _____ wire (brown) carries the supply, the neutral wire (blue) completes the circuit near 0 V, and the _____ wire (green and yellow) is a safety wire that carries current only in a _____.