Three wires, three jobs. Get which is which wrong and the appliance still works — right up until it kills someone. That is why this is examined so often.
This is the view you get with the back cover taken off, held so the earth pin is at the top. That orientation matters: it is the one every exam diagram uses, and it is what makes the left/right rule work.
| Wire | Colour | Function |
| Live | Brown right-hand terminal |
Carries the current from the mains supply to the appliance, at the high supply voltage of about 230 V. This is the dangerous wire — touching it completes a path to earth through your body. |
| Neutral | Blue left-hand terminal |
Completes the circuit, carrying the current back from the appliance to the supply. It sits at roughly 0 V, so it is the return path rather than the source of the danger. |
| Earth | Green and yellow top terminal |
A safety wire that carries no current in normal use. It connects the metal casing of the appliance to the ground. If a fault lets the live wire touch the casing, current flows to earth through this low-resistance path instead of through anyone touching it — and that large current blows the fuse, cutting the supply. |
The fuse is a deliberately thin piece of wire. If the current gets too large it heats up and melts, breaking the circuit.
It is placed in the live wire, not the neutral one, and that choice is the whole point. When the fuse blows, everything beyond it is cut off from the live supply, so the appliance is left at a safe voltage. Put the fuse in the neutral wire instead and it would still stop the current — but the appliance would stay connected to the 230 V live supply, so anyone opening it up could still get a fatal shock.
The cable grip clamps the outer insulation of the cable, not the individual wires. If someone tugs on the flex, the strain is taken by the grip rather than by the three screw terminals. Without it, a pull could drag a wire out of its terminal — and the loose wire touching the casing or another terminal is exactly the fault that causes shocks and fires.
Only three ratings are commonly used: 3 A, 5 A and 13 A. The rule is to work out the normal operating current, then pick the next standard fuse above it — high enough that the appliance runs without blowing the fuse, but as low as possible so a fault is caught quickly.
P = V × I → I = P ÷ V (mains V ≈ 230 V in Singapore)
A television is rated 920 W. Which fuse should be fitted?
I = P ÷ V = 920 ÷ 230 = 4 A
4 A is above the 3 A fuse, so a 3 A fuse would blow in normal use. The next rating up is 5 A — that is the correct choice. A 13 A fuse would let a dangerous fault current flow for far too long before blowing.
Nine questions, marked as you go. Get one wrong and you'll be shown why, plus how to work it out.