Cables, Plugs and Fuses Additional Physics

Learning Outcomes Most students should be able to: –Describe the design and function of a three-pin mains plug, including the choice of materials and the colours of the wires. –Recognise errors in the wiring of a three-pin plug. –Explain why it is necessary to connect some devices to the earth via the earth

Starter Can you guess what’s in the bag –Describe using shape and texture

The Three Pin 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. –The fuse breaks the current 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.

Can you do it? Wire a plug using what you’ve just learnt Wire a plug with a mistake and get your partner to fix it. Hint: When looking down onto a plug as it is being wired the BRown wire connects to the Bottom Right, the BLue wire connects to the Bottom Left. The other wire goes to the other pin! Remember: blue neutral brown live green and yellow stripes earth

What Does Each Wire do? In your book write down the function of each wire Neutral = Earth = Live =

EarthEarthEarthEarth 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. It acts as a back up for the neutral wire

Live and Neutral Live carries the current from the mains into the device The neutral wire carries it from the device back to the mains.

What Does Each Wire do? In your book write down the function of each wire –Neutral = This takes the current back to mains –Earth = Connects the metal casing to earth so it cannot become live –Live = The wire that carries the current to the device

Fuses Why do we need fuses? Demo: to high a current for a fuse A circuit breaker does the same job as a fuse but works in a slightly different way.

The fuse The fuse breaks the circuit if a fault in an appliance causes too much current flow. This protects the wiring and the appliance if something goes wrong. How? –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. The most common are 3A, 5A and 13A. 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

Plenary 3 pin plug – drag and drop activity Fuses worksheet that recaps the lesson content.

Learning Outcomes Most students should be able to: –Describe the design and function of a three-pin mains plug, including the choice of materials and the colours of the wires. –Recognise errors in the wiring of a three-pin plug. –Explain why it is necessary to connect some devices to the earth via the earth