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Understanding the basics of electricity.

If you are going to work on an electrical appliance always turn it off and unplug it before you start unless you need to work on it live.
If you are working on house wiring again always turn the power off and remove the fuse, keep the fuse in your pocket to prevent some one putting it back while you are still working on it.
Check your multi meter is working correctly by checking the voltage at a socket before you turn the mains off.

Having turned off the power and removed the fuse, check at a socket or appliance with a multi meter between live and neutral, between live and earth and between neutral and earth that there is definitely no power.

If you have one you can use a mains testing plug, there are quite cheap testers that plug into the mains socket. When the power is on they make a buzzing noise and various lights illuminate to indicate one of a number of possible conditions from correct operation to an assortment of faults that can exist (See photo below). The neat thing is that you can leave them plugged in and buzzing, go to your main fuse box and switch off the mains, you will know the power has defiantly gone off because the buzzing will stop.

Here is a photo of one.


Electrical circuits are based on some simple principles.
For an electrical appliance to work, the power must be able to flow along a wire from its source to the appliance, say a cooker, and then back to the source along another wire.
If the wire is broken at any point the electricity stops flowing and so the appliance will not work. Sometimes the circuit is broken deliberately with a switch. Turn the switch on and the circuit is completed and the appliance works, turn the switch off and the circuit is now ‘open’, the electricity cannot flow anywhere and the appliance will nor work.
Mains electricity to your home flows through a ‘live’ wire to every socket, light and fixed appliance in your house. The current flows out of the building after it has done its work, through the ‘Neutral’ wire.

The diagram below shows the ring main set up in a house in the UK.


Any material that current can flow through is called a conductor, the best conductors in a cable are made of copper because unlike steel or iron it does not corrode.
The earth on which we stand is also a good conductor especially if it is damp, this is why electricity always flows into the earth when ever it can always taking the shortest route, the route of least resistance.
This means that if you touch a live wire the electricity will take the easy route through you and down to earth, as it does so it can kill you by stopping your heart.
A similar thing can happen if a live wire touches a metal part of an appliance and then you touch it.
To prevent this happening a third wire is added to the cable and connected to the earth.
This earth wire is connected to any metal parts of an appliance or to any earth terminals provided.
This provides a low resistance path for electricity to go to earth if things go wrong, it reduces the chance of it going through you.
If this happens the sudden change of route and the sudden increase in current flow will blow a fuse or trip a circuit breaker so cutting off the electricity. However, it is not wise to rely on a fuse to cut off the electricity when there is a fault, it will probably blow but it might not be at exactly the rated value, or quick enough to stop you getting a shock.

Measuring electricity.

Measures the amount of power used by an appliance when it is working.
The wattage of an appliance is marked on the appliance. One thousand watts (1000W) is the same as one kilowatt (1kW).

Measures the flow of current that is necessary to produce the wattage for the appliance.

Measures the ‘Pressure’ provided by the electricity company. This drives the current along the wires to the various outlets or appliances. In the UK it is 230volts in the USA it is 110 volts.

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