What kind of fuse is usually fixed in a three-pin plug?

admin2009-06-24  3

问题 What kind of fuse is usually fixed in a three-pin plug?
  
Good evening, everyone! Welcome to our today’s Know-How. This time I’ll say something about wiring-up a three-pin plug, either because an old plug is broken or the cable has come loose, or because we have a new electrical appliance which needs a plug. All modern plugs have three rectangular pins and are sold with a 13A (ampere) fuse already fitted. A 13A fuse is the largest fuse used in the home for appliances taking a large electric current, such as an electric heater, a kettle, a color television, and a vacuum cleaner. Other appliances such as a black and white television, a food-mixer, a record player and an electric blanket need only a 3A fuse. Most cable contains three separate wires (three-core cable), each covered by colored plastic insulation according to an international code. The darkest color brown is the live wire. The live terminal in a three-pin, 13A plug is connected to the fuse, which controls how much current can pass through the appliance. If the current exceeds the limit of the fuse, the fuse will blow and the circuit is broken, thus allowing no current to pass into the appliance until the fuse is replaced with a new one. The green and yellow stripped wire is the earth wire; this ensures that the actual body of the appliance is kept at earth potential and that you cannot get an electric shock by merely using it and handling it in a normal way. The third wire, covered in blue, is the neutral wire.
    Some cables contain only two separate wires (two-core cable), live and neutral. This should only be used for small appliances, which take a low current, such as non-metal light fittings or transistor radios.
    The cable itself is covered in different materials depending on its weight and the use to which the cable is to be put. For example, radios, lamps and small appliances have a rubber or PVC covering, while washing machines, vacuum cleaners and electric irons are covered in heavy-duty rubber, sometimes covered by a braided cord. Appliances involving high temperatures have silicon rubber.
    Now let us discuss the correct way to wire-up a three-pin plug. You must take great care not to make a mistake; otherwise, a fire or damage to the appliance could he the result. You need only basic tools—a small screwdriver, a pair of wire strippers, a pair of scissors and a little insulation tape if you are using braided flex. The flex, of course, cannot be fitted into the plug until it has been prepared—this is done by cutting the outer covering of the flex with your scissors and stripping it back for about 50mm so that the three insulated wires are exposed. And before you do so, you must loosen the screw in the center of the plug with the screwdriver and hold the plug firmly in the palm of your hand with the pins facing upwards. After that, you can loosen the two small screws at the base of the plug, which hold the cord grip and then remove the fuse, which is clipped inside the plug. Prepare the flex as I explained earlier, wrapping insulation tape around the cut end if you are using braided flex and then run it underneath the cord grip, positioning the wires against their respective terminals, prior to cutting them to length. Only now are you ready to fit them to their terminals. To do this, you must strip 15mm of the colored insulation from each of the wires with the strippers. Be careful not to cut the wire as you do so. The green and yellow striped wire goes to the largest of the three pins, the brown wire goes to the terminal with the fuse and the neutral wire goes to the remaining pin. Before you fit the wires, however, you must first loosen the terminals and then twist the exposed wires clockwise to prevent any loose strands from escaping or touching each other. Fit the wires to the terminals out. The appropriate fuse for the appliance will be clipped into place after you have screwed the cord grip over the flex where it enters the plug and make sure that it is firm. And at last, you may replace the back of the plug and screw it—there should be no rattling if you have done the job properly.

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答案The central screw.

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