Domestic appliances use THREE-CORE CABLE with three wires:
1. LIVE WIRE — brown insulation
Carries the alternating pd (~230 V relative to earth).
DANGEROUS — carries current at high pd.
2. NEUTRAL WIRE — blue insulation
Completes the circuit. Normally at 0 V.
Can still carry current — still potentially dangerous.
3. EARTH WIRE — green and yellow striped insulation
Safety wire — carries NO CURRENT during normal operation.
Connected to the metal case of appliances.
If fault connects live to metal case → current flows through earth → fuse blows → circuit breaks → safe.
MEMORY: Live = Brown; Neutral = Blue; Earth = Green + Yellow.
Fuses, Circuit Breakers and Safety
FUSE: thin wire in series with live wire — MELTS if current exceeds safe level → circuit breaks.
Rated in amps. Choose just ABOVE normal operating current.
Common ratings: 1 A, 3 A, 5 A, 13 A.
CIRCUIT BREAKER: trips instead of melting — can be reset.
RCD (Residual Current Device): detects current imbalances — very fast response. Essential for bathrooms and outdoor use.
DOUBLE INSULATION:
Two layers of insulation between live parts and outer case.
No earth wire needed. Symbol: square within a square.
EXAMPLE — selecting fuse:
1 kW kettle at 230 V: I = 1000 ÷ 230 ≈ 4.3 A → use 5 A fuse.
Electrical Safety
WHY LIVE IS DANGEROUS:
Live is at ~230 V. Touching it while connected to earth → current through body → electric shock.
WHY FUSES AND SWITCHES GO IN THE LIVE WIRE:
If in the neutral wire → appliance still at 230 V when 'off' → dangerous.
In live wire → appliance fully isolated when switched off.
COMMON HAZARDS:
Frayed cables — exposed live wire.
Overloaded sockets — too many appliances → excess current → heat → fire.
Water near appliances — water conducts electricity.
Damaged plugs — loose connections.
⚠️ Common Mistake
Earth wire normally carries NO current — only activates in a fault. Neutral wire (blue) IS at ~0 V but CAN carry current. Fuses and switches must be in the LIVE wire so the appliance is fully isolated when switched off.
📌 Key Note
Live = brown (~230 V). Neutral = blue (0 V). Earth = green/yellow (safety, no normal current). Fuse in live wire — just above operating current. Earth wire diverts fault current → blows fuse → safe. Double insulation = no earth needed. Switches in live wire only.
🎯 Matching Activity — Three-Core Cable Wires
Match each wire to its colour, voltage and role. — drag the symbols on the right to match the component names on the left.
Live wire
Drop here
Neutral wire
Drop here
Earth wire
Drop here
Fuse
Drop here
In the live wire — melts if current exceeds safe value
Blue — at 0 V, completes the circuit back to the supply
Green and yellow — safety wire, normally carries no current
Brown — carries ~230 V alternating pd from the supply
🎯 Test Yourself
Question 1 of 2
1. Why must a fuse be in the live wire, not the neutral wire?
2. A metal-cased appliance develops a fault — live touches the case. What happens if it is properly earthed?
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