This article will deal with the electrical earth arrangements in a domestic dwelling in the UK. Contrary to a lot of peoples notions the earth is very necessary.
Why do we have an earth in our houses? To answer that requires a little explanation of how electricity reaches our homes and how fuses work.
Drill Electric
Electricity is generated at power stations or similar installations,
wind farms, hydro-electric turbines etc. These plants generate the electricity which is the transformed up to around four hundred thousand volts and distributed around the country via the national grid.
It is easy and cost effective to transport electricity at these incredibly high voltages but obviously it once again has to be transformed back down to 230 volts for use in the house.
At the transformer the centre of the winding is connected via rods or mats, to the earth. This earthing of the winding provides a reference point, nominally zero volts. Electricity is then supplied at 230 volts to this reference.
To be useful electricity requires a circuit. The electricity must flow from a source, through the device whatever it may be, kettle, iron cooker etc. and return to that source.
To protect the cable in which it flows the amount of electricity must not exceed the capability of the cable. This would be an overload in the long term, in the short term a fault in the cable or any device attached to it will cause a large amount of electricity to flow and it is this that blows the fuse.
The amount of electricity needed to blow a fuse is determined by the rating of the fuse itself, i.e. a current of around 1.6 times the fuse rating is required to operate a re-wirable fuse so a 20A fuse will need approximately 32 amps.
To facilitate the quick and efficient operation of the fuse the electrical earth provides a quick route back to the source, that is the transformer. The better the return path, the more electricity flows and the quicker the fuse operates.
The circuit that the live conductor and the earthing conductor form is called the earth loop. The earth loop is measured with a special tester and must conform to certain constraints for the variety of fuses available.
The requirements for each type of fuse, properly called a protective device, are laid down in the wiring regulations. The electrical earth therefore, is extremely important for the safety of any user of electrical system. The absence of the earthing conductor means that any fault on the system will not operate the fuse until you or one of your family becomes that missing part.
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Dec 23, 2011 12:56:12
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