WOODEN CASING AND CAPPING WIRING

WOODEN CASING AND CAPPING WIRING

WOODEN CASING AND CAPPING WIRING

The cables used in this type of wiring is eihter VIR or PVC or any other oppproved insulated cables.

The cables are carried through the wooden casing enclosures. The casing consists of V-shaped grooves (usually two to hold the cables of opposite polarity in different grooves) and is covered at the top by means of rectagular strip of wood, known as capping as capping of same width as that of casing.

The capping is screwed to the casing by means of 13 mm x 4 wooden screws fixed at every 15 cm on the center fillet.

To protect the casing against white ants first class seasoned teak wood varinshed by shellace varnish is employed.

Two or three cables of same polarity (either all phases or all neutrals) may be run in one groove.

The casing is usually placed 3.2 mm apart from the wall or ceiling by means of porcelain distance pieces of thickness not than 6.5 mm in order to keep the casing dry at the back.

The wooden gutties on which the casing is screwed by means of 32 mm x 8 wooden screws are fitted into walls or ceiling at intervals not exeeding 90 cm for sizes of caisng capping up to 64 mm exceeding 60 cm for sizes more than 64  mm. The sizes of the casing to be used depends upons the number and size of cables to be accommodated in any particular length of run.

The table II showing the number of cables of differnt sizes, which can be accommodated in each groove of differnt sizes of casing capping are given.

The length in which casing capping is available varies from 2.5 meters to 3 meters.

Advantages 

 1.  Chpeap in cost as compared to lead sheathed and conduit wiring system.

 2. Easy to instal and rewire.

 3. It provides good installation as conductors are good distance apart.

 4. Free from trouble of consdensation so advantageous in tropical countries where there might be trouble from condensation of moisture in steel conduit.

 5. Easy to inspect be opening the capping.

Disadvantages

 1.  This type of wiring even being coasted with paint or shellace varnish, is not damp proof so can not be used in damp places.

 2. Since there is a risk of fire,  so it can not be used where there is a possibility of fire hazard.

 3. This type of wiring can be used only on surface and can not be concealed in plaster.

Fields of application:

This type Of wiring of suitable for low voltage domestic installations in dry places and where there is no risk of fire hazard.

Precautions to be taken

 1.  The casing-capping used should be of first class seasoned striaght, smooth and hard teak wood.

 2. In no case the cables of opposite polarity should be run in one groove.

 3. The casing must be kept at least 3.2 mm apart from the walls or ceiling by means of porecelain distance pieces of thickness ont less than 6.5 mm in order to keep the casing dry at the back.

 4. The wooden gutties on which the casing is screwed must be fitted into walls or ceillings at an intervals not exceedings 90 cm for sizes of casing capping up to 64 mm and not excceding 60 cm. For sizes more than 64 mm.

 5. The casing should be well fixed fixed to its supporting structure i.e., walls or ceilings.

 6. Gaps should be avoided.

 7. At bends the grooves must be rounded off in order to save installation from damage.

 8. The joint whenever required should be made with good workmanship and in approved manner.

 9. All cappings, should be attached to the casings (after all insulated wirs are laid inside grooves) by round head screws (perferably of brass) fixed on edges and screwed to the outer walls of the casing at an interval not exceeding 15 cm cross-wise (i.e., 30 cm between successive screws one each side) for all sizes upto 64 mm casing and capping. For size above  64 mm similar additional round-head screws should be fixed on the center wall (or alternative walls in case of 3 grooves) at an interval of 45 cm.

10. While screwing capping over the casing precautions should be taken that screws go into the dividing wall of the casing otherwise they will damager the cable instalation.

11. The casing and capping should be painted with the paint as specified in I.S.732 before erection. It is also to be painted or varnished to give desired finish after erection.

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