Earthing: By connecting the metal case of an appliance to the Earth wire, any fault that causes the live wire to touch the case will result in a large current flowing to the ground rather than through a person.
Fuses: A fuse is a thin piece of wire connected in series with the live wire. If the current becomes too high (e.g., due to a short circuit), the fuse wire melts, breaking the circuit and preventing fire or further damage.
Circuit Breakers: These are electromagnetic switches that 'trip' (open) when the current exceeds a safe limit. Unlike fuses, they can be reset easily and respond much faster to current surges.
Double Insulation: Appliances with plastic casings do not require an earth wire because the casing itself is an insulator. These are marked with a 'square within a square' symbol.
| Feature | Alternating Current (AC) | Direct Current (DC) |
|---|---|---|
| Direction | Constantly reverses | Single, constant direction |
| Source | Power stations / Generators | Batteries / Cells |
| Voltage | Varies sinusoidally | Constant |
The National Grid is a system of cables and transformers that links power stations to consumers. It ensures a reliable supply of electricity across the country.
Step-up Transformers increase the voltage to very high levels (e.g., 400,000 V) for long-distance transmission. According to , increasing voltage allows the same power to be transmitted with a much lower current.
Efficiency: Lower current reduces energy loss due to heating in the transmission cables, as power loss is proportional to the square of the current ().
Step-down Transformers decrease the voltage to safer levels (230 V) for domestic use before the electricity enters homes.
The 'Second Letter' Rule: To remember wire positions in a plug, use the second letter of the color: bLue is Left, bRown is Right, and sTriped is Top.
Fuse Selection: Always choose a fuse rating slightly higher than the normal operating current of the appliance. For example, if an appliance draws 3 A, use a 5 A fuse, not a 3 A or 13 A fuse.
Calculation Check: When calculating power (), ensure units are standard (Watts, Volts, Amps). If given power in kW, multiply by 1,000 before calculating current.
Safety Logic: If asked why a person gets a shock, explain that the person is at 0 V (earth potential) and the live wire is at 230 V, creating a large potential difference that drives current through the body.
