The type of wiring to be adopted is dependent on following factors

The type of wiring to be adopted is dependent on following factors –

(a) Durability

(b) Safety

(c) Appearance

(d) Cost

(e) Accessibility

(f) Maintenance cost

(g) Flexibility

(h) Reliability

The various systems of wiring available are-

(i) Cleat wiring.

(ii) Wooden Casing & capping wiring

(iii) CTSOHs Batten wiring

(iv) Metal feed sheathed wiring

(v) Conduit wiring – surface/under ground

(i) Cleat wiring:

This type of wiring is used for temporary purposes such as for marriages, functions, etc.

The porcelain/Wood, cleats are easy to erect and fixed at a distance of 4 to 5 cm apart. VIR, p.v.C. Wires a normally used

Two on three wire (way) cleats are used us required. This system is, however, run on all kinds of surfaces and the cleats are fixed by means of raw plug or Gutties, wires or cables should be run without kicking and drawn tightly by screwing the cleat covers.

(i) Precautions:

It must not however be done on wet walls, underneath water or other pipes on which water might condense and drive on to the wires.

(ii) Wooden casing & capping wiring:

It is used for indoor & domestic installation. VIR wires are carried in double, triple channel of wooden casing & closed by wooden capping this type of wiring should not be used “when there is a danger of mechanical damage of fuse hazed.

(iii) CTS TRS Batten Wiring:

Wires are carried on batten with clips. This wiring is suitable for damp climate.

(iv) Metal lead sheathing wiring:

Wiring consists of rubber insulated con­ductor covered with another sheath of lead alloy which provides a protection to the cable from mechanical injury. The lend sheeting be earthed. The lead sheathed wires an easily fixed by means of metal clips on wood batten & forms a good surface.

(v) Conduit wiring:

PVC wires are carried through conduit.

The conduit wiring is undoubtedly the best wiring system. It has attained much importance for interior wiring installations. The conduits used may either be non-metallic (such as fibre, plastic or alkathin or metallic. The metallic con­duits may further be sub-divided into ferrous or non-ferrous.

The non-ferrous conduit may either be of aluminums or of copper. The ferrous conduits are made of mild steel; in its appearance it is similar to that of a water pipe, but they differ from it, in the sense that conduits are annealed to permit easy bending.

They are specially treated during manufacture so as to have high degree of corrosion re­sistance. In general the conduits can be classified as:

(1) Thin Wall conduits:

Such conduits are further sub-divided into:

(a) Close joint conduits:

These are made out of light gauge steel strips, bent so as to form a tube. There is no mechanical adhesion between its two edges. It is the cheapest form of conduit, and provides only mechanical protec­tion and covers risk against fire. Such conduits are not recommended for quality work.

(b) Brazed conduits:

Such conduits are also made similar to that of close- joint conduits, but the ends of the steel tubing are brazed together which makes the conduits damp-proof. It has the greatest disadvantage that the brazing mate­rial is left projecting inside the tube which makes drawing in of the wires impossible.

(2) Rigid Conduits:

Such conduits are made out of heavy gauge steel and the tube edges are electrically welded, so they are named as heavy gauge welded conduits.

There is another form of rigid conduit called as Solid drawn conduit. Such conduits are drawn from solids and have no joint throughout its section. They are the heaviest and the best, although a bit costlier.

These are available in about 3 meter lengths and are threaded at the two ends. The threads are usually tappered and are provided with a coupling on one side similar to that of plumbing pipe coupling. They can be joined together to form one continuous run.

While manufacturing conduits, care is taken to rebury, scale and other rough spots from inside of the tube to avoid damage of the insulation on the wires. Thus pulling in of the wires and cables easier.

There are two general types of finishes in which conduits are available.

(a) The black enameled conduits have a coating of black enamel, baked in a heating furnace, so that it may not peel off easily.

The black enamelled conduits should be used only for indoors. Their use should be avoided where the location is damp and where they are liable to face acid fumes, and salt sea water atmosphere.

(b) The “galvanized conduits” have a coating of zine which is usually ap­plied by hot dipping process.

(3) Flexible Conduits:

The flexible conduits are made from galvanized steel strips, specially wound upon each other.

(a) Concaved double strip:

It consists of concave-shaped steel strips spi­rally wound one upon the other. To make the conduit moisture-proof a gasket is provided in between the strips.

(b) Flat double strip:

The construction of this type of flexible conduit is similar to that in except that the strips are flat.

(c) Single strip:

This type of flexible conduit is made from a single galva­nized steel strip. Such strips are interlocked. These conduits may also be gasketed.

Usually the double strip conduits are preferred to single strip conduits since

(1) They are more flexible.

(2) They are smoother from inside.

The flexible conduits are available in lengths up to 250 metres, so no couplings are required and hence no threading required. The flexible conduits have advantageous application in installation where a certain amount of flexibility is required, is with motors having sliding bases.

However, the flexible conduit is costlier than the rigid conduit. Moreover it is not satisfactory in damp places as the moisture is liable to enter into the conduit. So embedding of such conduits into the concrete is avoided.

The general accessories required for the conduit installations are:-

(a) Couplings:

Since the conduits are available in smaller lengths, so to obtain & continuous length of the conduit the two are coupled together by means of coupling. For the three types of conduits (thin, rigid and flexible) different type of couplings are required:-

Thin wall conduit coupling:

The thin wall conduits cannot have threads, so coupling cannot be done in an ordinary way. There are two methods by which two conduit lengths can be joined together.

(a) The first method is by means of a slip socket joint in which case the two ends of the conduits are slipped inside a socket which is provided with collars against which the two ends butt. But this form of joint is not recommended as it does not provide a better electrically continuous joint.

When a flexible conduit is to be connected to a right conduit, a combination coupling is used. The combination coupling is similar to that of a split coupling with 4 screws, but one end of such a coupling is provided with threads for rigid conduit coupling represents such type of coupling.

(b) Elbows:

The change of direction in conduit wiring is always made by means of an elbow which provide a 90° bend Since the wires are to be pulled through the conduits after installation, it is necessary that the radius of the bend must be about 6 times the internal diameter of the conduit.

Usually the standard L’s are available in the market, but it is always a practice to bend the conduit at the site by means of hickey or by hand in pipe vice.

The offset due to ells is always more than the radius. While cutting conduits, care must be taken to allow for this offset. Since this offset is not the same for all sizes of conduit L’s, the usual practice adopted is not to cut the conduit until the L is fixed to the job.

(c) Conduit Bushings:

These are used when the rigid conduit enters the conduit box or when the conduit enter a hole which is not threaded It is either made from a malleable iron ore from a formed sheet steel. The bushings serve a double purpose.

(i) Firstly it prevents the insulation on the cables from being peeled off due to rubbing against the sharp edges of the conduit when they are pulled in;

(ii) Secondly it helps in securing the rigid conduit to conduit box when no locknut is placed on the inside of the box. Generally the collared bushing is used since it covers the hole in the board.

There is another closed type of bushing which is used during the construction of the building. Such type of bushing is provided with a cap. It prevents the moisture entering the conduit system during construction.

(d) Locknuts:

When the conduit enters a box, it is necessary that the look nut should be screwed on the conduit as it makes the connection to the box rigid and electrically continuous. The locknuts are punched out of thin steel sheets Locknuts are either hexagonal or octagonal.

(e) Conduit Nipples:

The nipples serve the same purpose as that of conduit bushing. Similar to the bushing it has & smooth inner surface and are used for providing a coupling to the conduit bore. The nipples are rarely provided because the system becomes costlier.

(f) Box Connector Bushings for Flexible Conduits:

Represents the bushing to be used when the flexible conduit enters the box. The connectors so used are usually made of cast iron; one end of it clamps the flexible conduit while the other threaded end enters the bore where it is fixed to the box with the locknut.

(g) Conduit Reducers:

The reducers are used when the size of the conduit is changed in between the wiring system. The conduit reducers are similar to that of steam and water-pipe reducers. Fig. 3.204 shows a reducer changing a 19.0 mm to 125 mm conduit pipe. In practice the size of the conduit cussed in to one building is not changed.

(h) Conduit Box:

The rigid conduits are always terminated at outlets into a box. There are different types of boxes; it may be round, square or octagonal. The depth of the box may be.

The boxes always have knockouts punch out at the time of manufacture and are held there by small sections of knockouts: these knockouts are removed by hammering, or with the twist motion of the pliers or a blunt tool.

The conduit boxes are also called as outlet boxes since they are usually used for outlets. The boxes are provided with a cover held by screw on it.

After removing the knockout the conduit is attached to it by means of the locknut and bushing. Care should always be taken not to remove the knockout until and unless it is to be used; the knockout is removed it must be sealed. The purposes for which the boxes are used are underlined:

(i) To provide connections for lights, fans, heaters etc, in which case they are called as outlet boxes;

(ii) To facilitate the pulling of conductors in the conduits and are known as inspection boxes;

(iii) To house the junctions of the conductors and are known as junction boxes;

(iv) To provide snap switches.

It should be noted that if the conduit to be fixed to the box it is cut too long so that two locknuts are provided, one inside the box & the other outside,

(I) Conduit Saddles or Clamps or Straps:

The conduit straps or saddles are used to fix the conduit to the wooden plugs in the wall. The conduit saddle may have one or two such saddles are made from sheet steel.

(J) Conduit Fittings:

The conduit fittings are similar to that of a box ; but the difference lies only in the method of fixing the conduit to these. The conduit fittings have projections and have female threads. The use of boxes are generally limited to the concealed type wiring as the conduit fittings are rarely used for that, but for the surface work both fittings and boxes can be used

There are two methods of fishing the wire in conduits:

(i) In case of one-way fishing only one snake wire is used for pulling the wires;

(ii) Where the conduit runs are very long and have a number of bends close together, those require two-way fishing i.e. two snake wires are pushed in, one from each end of the conduit. The wires in the conduit are so manipulated that their hooked ends engage each other. Then one of the wires is pulled through the conduit, Usually it is a job of two men, in order that the wires may engage easily, one of the workers shakes and rattles it while the other worker tries to get it engaged with the other snake wire.

In fishing operation care must be taken that:

(i) there should not be any kink or bend in the wire entering the conduit.

(ii) the wires in the conduit should not cross.