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Describe factory systems of distribution, and state typical applications.Distribution: flexible and rigid conduits, trailing cables and overhead collector,

Bus-Bar trunking, Underfloor ducting, cable trunking, rising mains,

PILCSWA, PVCSWA, and MIMS cables

Tailored By

Obaid ur Rehman

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Conduits

A conduit is a tube, channel or pipe in which insulated

conductors are contained. The conduit, in effect, replaces the PVC outer sheath of

a cable, providing mechanical protection for the insulated conductors.

There are three types of conduit used in electrical installation work:

Steel

PVCFlexible.

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Steel Conduits

Conduits made up of steel are known as Steel Conduits, specification

defined by BS 4568 (British Standard) either heavy gauge welded or solid

drawn (seamless). Seamless Conduits are comparatively expensive and only

used for special gas-tight, explosion-proof or flame proof installations.

The metal conduit is also utilized as the circuit protective conductor and,

therefore, all connections must be screwed up tightly and all burrs removed so

that cables will not be damaged as they are drawn into the conduit.

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Advantages of Steel Conduit

Provides Very Good Protection to the conductors.

Rewiring or limited additional wiring is fairly easy.

Does not burn.

The steel has low resistance it can be used as the earth conductor.

Disadvantages of Steel Conduit

It can corrode

Expensive to Install.

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PVC Conduit

PVC Conduit is made up of (Poly Vinyl Chloride), The advantages of a PVC

conduit system are that it may be installed much more quickly than steel

conduit and is non-corrosive, but it does not have the mechanical strength of

steel conduit.

PVC conduit is an insulator it cannot be used as the CPC (Circuit Protective

Conductor) and a separate earth conductor must be run to every outlet. It is

not suitable for installations subjected to temperatures below -5C or above60C

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Advantages of PVC Conduit Lightweight

Easy to work, that is cut, join and bend.

Non Corrosive

Very Good Insulator

Disadvantages of PVC Conduit Cannot be used as the earth conductor.

High Temperature constraint.

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FlexibleConduit

Flexible conduit is made of interlinked metal spirals often covered with a PVC

sleeving.

Flexible conduit is used for the final connection to motors so that the vibrations of

the motor are not transmitted throughout the electrical installation and to allow

for modifications to be made to the final motor position and drive belt

adjustments.

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Trunking-Installations

A trunking is an enclosure provided for the protection of cables which isnormally square or rectangular in cross-section, having one removable side.Trunking may be thought of as a more accessible conduit system and forindustrial and commercial installations it is replacing the larger conduit sizes.

Most trunking is available in either steel or plastic. and the standard bend. If anearth continuity test on the trunking is found to be unsatisfactory, aninsulated CPC must be installed inside the trunking. The Various types ofTrunking are.

Metallic trunking

Non-metallic trunking

Mini-trunking

Skirting trunking

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Rising Main Bus-Bar Trunking Overhead Bus-Bar Trunking

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Bus-Bar Trunking

The electricity supply is brought into the ground floor of a building and if there are

number of floors the supply to the upper floors is via rising mains straight

from the bottom of the building to the top . This rising main is often made fromuninsulated copper Bus-Bars fixed in vertical trunking.

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Overhead Collector and Trailing CablesSometimes it is necessary to have a movable supply of electricity, say across a

factory floor. This can be achieved by installing a bus-bar system above the

required route and to it is fixed a trailing cable which can be moved along the

bus-bar to feed the required point on the floor.

This system is particularly useful where portable equipment, such as a welder is

required to be used almost anywhere in the factory.

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PVCSWA ( Poly Vinyl Chloride Steel Wire Armored Cable)

PVCSWA is the most common cable for underground use between buildings, for

incoming supply and Installations in factories etc.

http://localhost/var/www/apps/conversion/tmp/scratch_3/PVCSWA.dochttp://localhost/var/www/apps/conversion/tmp/scratch_3/PVCSWA.dochttp://localhost/var/www/apps/conversion/tmp/scratch_3/PVCSWA.dochttp://localhost/var/www/apps/conversion/tmp/scratch_3/PVCSWA.doc

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PILCSWA

Paper Insulated CablesPVC is by far the most common form of insulation between the conductors of a

cable. In earlier times oil impregnated paper was commonly used and is still

used and is still used for high voltage, say 132 KV normally underground,

cables.

The advantages of oil impregnated paper is that oil and paper are very good

insulators, and the oil fills small gaps which would otherwise exist in the

insulation layer.

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