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
Brown — carries ~230 V alternating pd from the supply
Green and yellow — safety wire, normally carries no current
In the live wire — melts if current exceeds safe value
Blue — at 0 V, completes the circuit back to 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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