NGfL CYMRU GCaD ELECTRICAL WORKS DISCLAIMER Neither WJEC or NGfL accepts any responsibility...

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NGfL CYMRU GCaD www.ngfl-cymru.org.uk ELECTRICAL WORKS DISCLAIMER Neither WJEC or NGfL accepts any responsibility whatsoever for any injury, however caused, relating to or resulting from this document. By reading this, the reader accepts and agrees that neither WJEC or NGfL are providing training, intentionally or unintentionally for carrying out electrical works.

Transcript of NGfL CYMRU GCaD ELECTRICAL WORKS DISCLAIMER Neither WJEC or NGfL accepts any responsibility...

Page 1: NGfL CYMRU GCaD  ELECTRICAL WORKS DISCLAIMER Neither WJEC or NGfL accepts any responsibility whatsoever for any injury, however caused,

NGfL CYMRU GCaD

www.ngfl-cymru.org.uk

ELECTRICAL WORKS

DISCLAIMERNeither WJEC or NGfL accepts any responsibility whatsoever for any injury, however caused, relating to or resulting from this document. By reading this, the reader accepts and agrees that neither WJEC or NGfL are providing training, intentionally or unintentionally for carrying out electrical works.

Welsh Joint Education Committee
Page 2: NGfL CYMRU GCaD  ELECTRICAL WORKS DISCLAIMER Neither WJEC or NGfL accepts any responsibility whatsoever for any injury, however caused,

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ELECTRICAL WORKS

CABLE SIZES

Correctly sized cables should be selected so that the cable meets the power demands of the equipment it serves.

Cable sizes are stated in square millimetres, which is the cross-sectional area of the wire inside. The larger this area is, the higher the current, or load, it can carry.

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Fire can occur where a cable is too small for the amount of current carried.

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Generally, electrical cables consist of three parts, namely:-

Conductors, which carry electricity. Insulators, which insulate the conductors. Protective jacket, which protects the insulation and

conductors.

This applies to cables supplying small electrical devices, such as computers, monitors, domestic appliances etc.

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Large incoming electricity supplies are brought into buildings

on three-phase supplies.

ELECTRICAL WORKS

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‘Three-phase’ means that three separate circuit conductors bring electricity into a building at the same frequency (also known as a cycle), one-third of a cycle apart. At any one time, a scenario could be:-

L1 Brown phase at peak valueL2 Black phase at 2/3rds valueL3 Grey phase at 1/3rd value

Neutral Phase – blue – allows the 3 phase supply to run simultaneously as a single phase supply.

ELECTRICAL WORKS

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Supply cables are sometimes brought into a building via underground ducts through the foundations. The cables shown left are over 50mm in diameter, and originate from electrical sub-stations.

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A main distribution board sends electricity to smaller distribution board that are placed throughout a building. At each stage of distribution, the voltage is reduced until it reaches 240 volts drawing 13 amps of current.

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Distribution board before cables are connected.

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A local distribution board. The blanks (indicated by the red arrow) provide spare capacity, which have not been used but could supply additional circuits in the future.

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A list, or schedule inside each distribution board shows which circuits are served by the distribution board.

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Cables may be left exposed, as in the above photograph.

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Alternatively, cables may be hidden. In the picture shown above, the cables are concealed in the body of the lamp fitting, and through the spotlight rail.

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Different cables are used for different purposes: the above image shows data cables supplying information via a file server and an Information Technology network.

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Above – network cables before being pulled, or placed in position. Cables are tied together to form looms to help cable installation.

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Above: data cables (orange in colour) drawn into position. Power cables run in the plastic dado trunking above the data cables.

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In order to prevent damage, cables are often placed in steel mesh cable trays. These can be fixed to walls or soffits (ceilings) of a building.

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Cables can also be contained in surface-mounted plastic ducts.

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This photo shows the correct

fitting and fixing of cables.

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The next two slides show how cables should not be fixed.

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Incorrect installation

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Incorrect installation

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Cables awaiting fixing inside a distribution board.

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ELECTRICAL WORKS

ALWAYS REMEMBER!

Electricity, in the wrong hands, can kill.

NEVER start work or touch electrical equipment unless you have been trained and items have been isolated.

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ELECTRICAL WORKS

DISCLAIMERNeither WJEC or NGfL accepts any

responsibility whatsoever for any injury, however caused, relating to or resulting from this document. By reading this, the reader accepts and agrees that neither WJEC or NGfL are providing training,

intentionally or unintentionally for carrying out electrical works.

Welsh Joint Education Committee