The electrical wiring and appliances in the majority of houses are protected by fuses and in newer installations, by circuit breakers. Fuses and circuit breakers are protection devices for houses; they react to any short circuit or overload and cut off the power by burning the fuse or by clicking out of the circuit breaker.
Fuses can be changed by homes owners, and circuit breakers can simply be reset. It is important to always use the correct fuse wire: because two pieces of wire look the same it does not mean that they will both protect in the same way or in the same time.
Two standard wires are used, and are available on a card from every hardware store. The ratings are:
Why fuses blowThe two ratings are not interchangeable. Fuses and circuit breakers will not necessarily blow quickly enough to stop electrocution of a person. Protection against accidental shock is best ensured by continual diligence and the use of residual current interrupters (these measure any slight current imbalance).
Replacing a fuse
To replace a fuse, first turn off the switch controlling the circuit on which are you are working. This may be the main switch. Then take out the ceramic or plastic fuse block and partly unscrew the two screws holding the wire in place. You can then remove the remaining burnt ends of the wire.
Install the correct new wire by feeding it through the hole in the block. Then wind its end once around once screw in the tightening direction of the screw. Tighten the screw to hold the wire securely. Do not over-tighten as the wire may break.
Pull the wire until it is reasonably taut and it reaches the other screw. Again, wind the wire around the screw once only and tighten it. Rotate the loose end of the wire around the screw until breaks off.
Reinstall the fuse in the fuse holder; ensure that all interior switches controlled by that fuse are off, turn on the main switch and then gradually turn on the interior appliances or lights.
Fuses blow due to overloading or a fault in the wiring or an appliance. A fault will normally cause the fuse to blow straight away. Overloading will take a little longer, as the fuse heats up before finally blowing.
Faults in the lighting circuit should be checked by an electrician because this is normally caused by a fault in the fixed wiring or fittings or in the switches themselves.
If a power circuit blows, check to see how many appliances are connected to that circuit. A power circuit is rated at 15 amps which will allow to a maximum of 3600 watts of appliances to be used at once.
The formula commonly used to calculate the wattage that can be run off a circuit is:
Voltage x amps = watts
Voltage is always 240V, and the amps are either 15 amps for power circuits or 8 amps for lighting. Watts are sometimes given as volt amps. To work out the load on a circuit simply add up the wattages on the compliance plates of the appliances being used. As a general guide the following may help if wattages cannot be found:
APPLIANCE WATTAGE
Dishwasher 1000-2500
Electric radiator 1000-2400
Kettle 1500
Electric frypan 1400
Toaster 1300
Clothes dryer 1000
Coffee percolator 650
Waste disposal unit 650
Microwave oven 600-1000
Vacuum cleaner 600-800
Mixer 150
Rangehood 150
Refrigerator 100-400
Reading lamp 75-100
Stereo 60-200
Electric clock 2
If, after totaling up the load, you find that it is not over the limit, switch on with a new fuse. If it blows again there is probably a faulty in the circuit or in an appliance and this will have to be found.Notice that appliances with heating elements consume a high amount of energy, followed by appliances with powerful electric motors. When a heater, kettle, toaster and clothes dryer are operating on the one circuit, you will have a problems.
If the fault lies in an appliance, it can be easily found by switching on each appliance one by one to see which one causes the system to blow. The faulty appliance must be repaired by an electrician or an approved repair or service centre.
If the problem is in the circuit, it will blow the fuse immediately. An electrician should be called to repair the circuit.