Page 100 - Electrician - TT (Volume 1)
P. 100

ELECTRICIAN - CITS




           It is a simple system and cheapest method of wiring. Mainly used for temporary wiring purpose. It is installed 1.5
           metres above the ground level. Single core VIR or PVC insulated cables are used. Porcelain or wooden cleats
           of two way , three way, four way etc are available. For fixing cleats on wall wooden plugs (gutties) and wood
           screws are used. For avoiding sag in the cable , cleats are provided every 60.cm distance. In branch circuit the
           distance between cable should be 2.5 cm. In sub main circuit the distance between cable should be 4 cm. The
           cables are prevented to avoid coming in contact with other conductors , gas  or water mains. Cross - cleated
           cables should be separated by an insulating bridge piece which should at least maintain a distance of 1.3 cm
           between the cable. In this wiring ,  joints are to be maid in wooden or other insulating material  junction boxes with
           porcelain connectors inside. Two wires should never be placed in the same grove of the cleats. Life of this wiring
           is approximate 5 – years. This wiring is not used in damp walls or ceiling. Wiring must be enclosed in  conduit if
           the wire is passing through  a wall or a floor.
           Advantage
           The wiring can be completed very fast.

           Faults can easily be located
           Disadvantage
           It collects dust over the wire
           There is no protection from mechanical injury
           Casing and capping

           Wooden casing and capping wiring
           This wiring is suitable for  low voltage domestic installation. In this system of wiring vulcanised rubber-insulated
           cables or PVC insulated cables  are used. It is not suitable in damp places. The casing and capping  should be
           of well seasoned teak wood or any other hard wood . Before the installation of casing capping it should be well
           varnished from all sides with shellac varnish. The casing is fixed by means of flat head counter sunk wooden
           screws to the wooden plugs(gutties) on wall or ceiling. The distance between two casing fixing wooden screws is
           not exceeding 90 cm for sizes up to 64 mm and not exceeding 60 cm for sizes above 64mm casing . The capping
           is fixed on casing by means of round head brass screws at a distance not exceeding 15 cm cross-wise for all
           sizes up to 64 mm casing capping. For cap sizes above 64.mm the screws are fixed at an interval of 22.5.cm
           cross-wise on  capping. The life of this wiring is approx. 20 years. While laying out the casing try to avoid corners
           and crossing of cables as  far as possible .If this cannot be avoided ,then use wooden corners and bridge pieces.
           This type of wiring is commonly used in residential and office buildings. The selection of casing and capping size
           depends up on the number of wires drawn through the groves. Any number of wires of the same polarity , either
           phase or neutral , may be laid in  the same grove. The opposite polarity of wires should never be laid in one grove.
           In this type of wiring, there is a clearance of 0.32 cm thick space  between the wall or ceiling and the casing by
           means of porcelain insulators .
           Advantage
           •  Mechanical protection is good
           Disadvantage

           •  There is great risk of fire in this system
           •  It is difficult to find fault
           •  If it is not damp proof it absorbs moisture easily
           •  Its erection is not very simple and requires more time

           •  Skilled labour is required













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 CITS : Power - Electrician & Wireman - Lesson 20-25  CITS : Power - Electrician & Wireman - Lesson 20-25
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