Earthing works by providing a low-resistance path to the ground. If a fault causes the live wire to touch a metal case, a massive current flows through the earth wire instead of through a person touching the case.
A Fuse is a safety component containing a thin wire designed to melt if the current exceeds a specific rating. It is always connected in series with the Live wire.
When a fault occurs and the earth wire draws a large current, the surge causes the fuse to blow, immediately breaking the circuit and isolating the appliance from the high-voltage supply.
| Feature | Live Wire | Neutral Wire | Earth Wire |
|---|---|---|---|
| Color | Brown | Blue | Green/Yellow |
| Voltage | (nominal) | ||
| Function | Supplies power | Completes circuit | Safety/Grounding |
| Danger | High (Lethal) | Low (but not zero) | None (normal use) |
Mnemonic for Wiring: Use the 'second letter' rule to remember positions in a plug: bLue is Left (Neutral), bRown is Right (Live), and sTriped is Top (Earth).
Safety Logic: Always explain safety features as a two-step process: the Earth wire provides a low-resistance path, which then causes the fuse to blow. Mentioning only one part often results in partial marks.
Standard Values: Be prepared to state the UK mains frequency () and potential difference () from memory, as these are frequently tested constants.
Double Insulation: Recognize that appliances with plastic cases (double insulated) do not require an Earth wire because the casing cannot conduct electricity even if a fault occurs.
