Electrical Safety
Visão Geral
The mains supply that powers your home is useful and dangerous in equal measure. A frayed cable, a damp room or an overloaded socket can cause a shock or a fire, so every house and appliance is built with layers of protection you may never notice.
In this lesson you will learn the hazards of mains electricity and the safety features that guard against them: the three wires of a mains circuit, why the switch and fuse go in the live wire, how fuses and trip switches work, and why appliances are earthed or double-insulated.
Objetivos
- State the hazards of: (a) damaged insulation (b) overheating cables (c) damp conditions (d) excess current from overloading of plugs, extension leads, single and multiple sockets when using a mains supply
- Know that a mains circuit consists of a live wire (line wire), a neutral wire and an earth wire and explain why a switch must be connected to the live wire for the circuit to be switched off safely
- Explain the use and operation of trip switches and fuses and choose appropriate fuse ratings and trip switch settings
- Explain why the outer casing of an electrical appliance must be either non-conducting (double-insulated) or earthed
- State that a fuse without an earth wire protects the circuit and the cabling for a double- insulated appliance
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- A switch must be connected in the live wire so that, when off: A. the appliance still works B. the appliance is disconnected from the live voltage C. the neutral is broken D. the earth is connected Answer: B
- A fuse protects a circuit by: A. increasing the current B. melting and breaking the circuit if the current is too high C. earthing the case D. storing charge Answer: B
- Which is NOT a hazard of mains electricity? A. damaged insulation B. overheating cables C. a correctly rated fuse D. damp conditions Answer: C
- An appliance with a plastic case that needs no earth wire is: A. earthed B. double-insulated C. unfused D. short-circuited Answer: B
- An appliance normally draws 9 A. The most suitable fuse is: A. 3 A B. 5 A C. 13 A D. 1 A Answer: C
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