Electrical Safety

1. Electrical Safety Noadswood Science, 2012

2. Electricity Safety • To be able identify safety features with electrical components

3. Mains Electricity • There are various electrical hazards within the home – most are common sense, and can be eliminated easily, with a basic list compromising of: - • Long or frayed cables • Cables in contact with something hot or wet • Children and pets (hamsters, rabbits etc…) • Water near sockets • Shoving things into sockets • Damaged plugs / too many plugs within a socket • Lighting sockets without bulbs in • Appliances without covers

4. 3 Pin Plug – the cable • A mains electricity cable contains two or three inner wires – each has a core of copper, because copper is a good conductor of electricity • The outer layers are flexible plastic, because plastic is a good electrical insulator • The inner wires are colour coded: - • Blue – neutral • Brown – live • Green / yellow stripes – earth

5. Plug • The features of a plug are: - • The case is made from tough plastic or rubber, because these materials are good electrical insulators • The three pins are made from brass, which is a good conductor of electricity • There is a fuse between the live terminal and the live pin • There is a fuse between the live terminal and the live pin • The fuse breaks the circuit if too much current flows • The cable is secured in the plug by a cable grip – this should grip the cable itself, and not the individual wires inside it

6. Wire Placement • There is an easy way to remember where to connect each wire • Take the second letters of the words blue, brown and striped – this reminds you that when you look into a plug from above: - • Blue goes left • Brown goes right • Striped (green / yellow) goes to the top

7. Wiring • Practice wiring up the 3-pin plugs… • Can you identify the deliberately damaged plugs and explain how they are damaged / how this could be rectified? • Blue goes left • Brown goes right • Striped (green / yellow) goes to the top

8. Earthing • Many electrical appliances have metal cases, including cookers, washing machines and refrigerators – the earth wire creates a safe route for the current to flow through if the live wire touches the casing • You will get an electric shock if the live wire inside an appliance, such as a cooker, comes loose and touches the metal casing • The earth terminal is connected to the metal casing so that the current goes through the earth wire instead of causing an electric shock • A strong current surges through the earth wire because it has a very low resistance – this breaks the fuse and disconnects the appliance

9. Fuses & Circuit Breakers • Fuses and circuit breakers protect electrical circuits and appliances

10. Fuses • The fuse breaks the circuit if a fault in an appliance causes too much current flow, protecting the wiring and the appliance • The fuse contains a piece of wire that melts easily – if the current going through the fuse is too great, the wire heats up until it melts and breaks the circuit • Fuses in plugs are made in standard ratings (3A, 5A, 13A etc…) • The fuse should be rated at a slightly higher current than the device needs: - • If the device works at 3A, use a 5A fuse • If the device works at 10A, use a 13A fuse etc…

11. Circuit Breakers • The circuit breaker does the same job as the fuse, but works slightly differently – a spring-loaded push switch is held in the closed position by a spring-loaded soft iron bolt • An electromagnet is arranged so that it can pull the bolt away from the switch • If the current increases beyond a set limit, the electromagnet pulls the bolt towards itself, which releases the push switch into the open position Circuit working Circuit broken

12. RCCBs • Residual current circuit breakers (RCCBs) are a type of circuit breaker used instead of a fuse or Earth wire • Normally exactly the same current flows through the live and neutral wires – if the live is touched a current flows through them to the Earth (which is extremely dangerous) • This also causes the neutral to carry less current than the live which is detected by the RCCB and it cuts the power by opening a switch • RCCBs operate a lot faster than fuses making them safer, and they also work for a small change in current (unlike a fuse which needs to melt so requires a large current change). RCCBs can also be flicked back on!

13. Shock Prevention • If a fault develops in which the live touches the metal case, then because the case is earthed a big current flows through the live, through the case, and out down the earth wire • This surge in current also blows the fuse (or trips the circuit breaker) which cuts off the live supply • This two systems isolate the appliance, making it impossible to get an electric shock from the case (as well as preventing fire due to the heating effects of large currents) • *If an appliance has a plastic casing with no metal parts showing it is double insulated (and it doesn’t need an earth wire)

14. Plug Safety Features • Complete the plug safety features worksheet • Key words: - • Large • Harm • Safety • Melt • Live • Circuit • Fuse