Electrical Safety · revision map · IGCSE 0625, Topic 4.4
TOPIC 4.4 · ELECTRICAL SAFETY
CAMBRIDGE IGCSE PHYSICS 0625 · ONE-PAGE REVISION MAP
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ELECTRICAL
SAFETY4.4
SAFETY4.4
Electrical Hazards
Most mains dangers come from a few common faults that let current reach a person or start a fire.
- Damaged insulation exposes live wires.
- Water and damp let current pass to you.
- Overloaded sockets and coiled cables overheat.
- Long trailing leads and cracked casings.
- Pushing objects into a socket.
Live, Neutral & Earth
A three-pin plug connects an appliance to the mains safely.
- Live (brown) carries the supply; the fuse sits here.
- Neutral (blue) completes the circuit.
- Earth (green/yellow) is a safety path.
Fuses
A fuse is a thin wire in the live wire that melts if the current gets too large, breaking the circuit.
P = V Iused to size a fuse: current I = P ÷ V; choose a rating just above the normal current.
Circuit Breakers
A circuit breaker is a switch that trips and opens the circuit if the current rises too high.
- Does the same job as a fuse, but faster.
- Can be reset instead of replaced.
Earthing
Earthing stops a metal case from becoming dangerous if a live wire touches it.
- The metal case is joined to the earth wire.
- A fault sends a large current safely to earth.
- This blows the fuse and cuts off the supply.
Double Insulation
A double-insulated appliance protects the user without an earth wire.
- It has a plastic (insulating) case, so the outside can never become live.
- Only the live and neutral wires are needed; it has no earth.
- Marked with the double-square symbol.
BUILDS ON · Electrical quantities · Circuits
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ELECTRICAL SAFETY
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LEADS TO · Electromagnetic effects