Electrical safety
Hazards of electricity, fuses, circuit breakers, earthing and double insulation.
Review these first
Learning objectives
What you need to be able to do
Teacher-mapped phrasing — check against the official Cambridge syllabus for exact wording.
- 4.4.1Identify electrical hazards including damaged insulation, overheating cables, damp conditions and excess current.
- 4.4.2Explain the use of fuses, circuit breakers and earthing in domestic circuits.
6 minute read
Electrical safety
Hazards
Common electrical hazards include: damaged or frayed insulation (exposing live wires), overheating cables (from carrying too much current, or being coiled up so heat cannot escape), damp conditions (water conducts electricity, increasing the risk of shock), and too many appliances on one socket, drawing excess current.
Fuses
A fuse is a thin wire that melts and breaks the circuit if the current becomes too large, protecting the appliance and its wiring from overheating and catching fire. The fuse rating is chosen just above the appliance's normal operating current.
Circuit breakers
A circuit breaker does the same protective job as a fuse — cutting off current that is too high — but uses an electromagnetic switch instead of a melting wire, so it can be reset and reused rather than replaced.
Earthing
The earth wire connects the metal casing of an appliance to the ground, providing a very low-resistance path. If a fault causes the live wire to touch the casing, a large current flows through the earth wire rather than through anyone touching the case, and this surge immediately blows the fuse, cutting off the supply.
Double insulation is an alternative: the appliance is built with two layers of insulation and no exposed metal parts at all, so there is no need for an earth wire.
Think of it like this
A fuse is a deliberately weak link — like a small drawbridge designed to collapse safely under too much weight, protecting the much more valuable bridge (the appliance and its wiring) from being destroyed by an overload it was never designed to survive.
Common misconceptions
- Thinking a fuse or circuit breaker directly protects a person from shock. Their job is to prevent excessive current from damaging the wiring and causing a fire; earthing is what protects a person by giving a fault current a safer path than through their body.
- Believing a blown fuse can simply be reset like a circuit breaker. A fuse wire has melted and must be physically replaced.
- Assuming any current is dangerous. It is specifically excess current — beyond what the cable and appliance are rated for — that fuses and circuit breakers are designed to detect and stop.
In the exam
- Explaining earthing needs the full chain: low-resistance path → large fault current flows to earth instead of through a person → this trips the fuse → supply is disconnected. Each link is usually worth its own mark.
- When choosing a fuse rating, pick the smallest standard value (commonly 3 A, 5 A or 13 A) that is still above the appliance's normal operating current.