Normally, the best type of draw-in box to use is the round inspection box. These have a better appearance, plenty of room for drawing in cable, and have enough room to stow slack cable. For conduits up to 1 in. diameter small round boxes of inside diameter 23/8 should be used. The large round boxes, having an inside diameter of 3/6 are suitable for conduits not larger than lin. diameter. For conduit larger than 1/2 diameter, rectangular boxes should he used. The reason for this is that generally larger size cables are run in the larger diameter conduits, and with round draw-in boxes not enough space is available to draw the cables in or stow the slack. Rectangular boxes are made in various size and they should be chosen so that they are long enough to permit easy drawing in. The inspection sleeve is a useful fitting because its length makes it easy to draw in even relatively large size cables. Its marrow width also enables conduits to be run close together without, making any sets in the conduit to avoid the draw-in points.
Where two or more conduits are run in parallel, it is good practice to provide, an adaptable box (made of cast iron or pressed steel), to which all the conduits can be connected. This gives a better appearance than separate draw — in boxes and has the advantage of a junction point if additions to the installations have to be made later. One advantage of the conduit system is that the cables can be altered or renewed at any time. In order to make this s easy as possible all draw-in boxes should be readily accessible and nothing should be fixed over or in front of them.
If conduit has to be run straight for distances which are longer than the standard lengths’ supplied, then joints will have to be made in the conduit. This can either be done by screwed couplings when the conduit is able to be rotated, or by running joints if the conduit cannot be moved. Conduit Fixing These provide a good secure fixing for surface conduit and can be used where it is not necessary to keep the conduit run away from the surface. Saddles should be spaced at intervals of about 3 ft. along the conduit, and within 4 in. of each fitting or accessory. When fixing these saddles to concrete, stone, brick or plaster walls, Rawl-plugs or similar plugs should be used. They should be secured by round headed brass or rust proofed screws of 1 inch minimum length. Space Bar Saddles These are ordinary saddles mounted on a spacing plate. These plates should be ½ in diameter and 3 in, thick for larger sizes of conduit. This spacing plate is approximately the same thickness as the sockets and other conduit fittings, and so the conduit need not be set out ‘hen it leaves these fittings. It also prevents the conduit from coming into close contact with damp walls or ceilings, thus preventing corrosion of the conduit.
Generally spacer bar saddles have only one fixing hole in the centre, the saddle being fixed to the bar by small screws. This then saves time in installation as only one hole has to be plugged instead of two and the fixing of the conduit is easier. The intervals of fixing along the conduit are the same as with ordinary saddles: Distance Saddles These are made so as to space the conduit approximately 3/8 in. from the wall or ceiling, and can be made of cast iron. They are much stronger than the ordinary type of saddle and provide protection against corrosion since they keep the conduit further from the wall. They are usually specified for installations where cleanliness is essential, such as out of reach conduit runs in hospitals; the increased spacing from the wall prevents the collection of dust and dirt behind the conduit. Multiple Saddles These are used where two or more runs of conduit follow the same route. Different types are available but use of the type which clamps the conduits close together is not recommended. The better practice would be to use a number of ordinary saddlew which leave a reasonable space between each run of conduit and give more secure fixing. The intervals of fixing along the conduit should be about the same as for a single run, but with a large number of conduits, the intervals might have to be shorter. Girder Clips These are used where conduits are run along or across steel girders or joists. Standard sizes are available hut it is generally better to make them up on site since they can be made to fit the conduit and the girder exactly. Clips should be spaced at intervals of about 3 ft. along the conduit.
When conduits are being suspended across girders and held by these clips, there is a possibility of sagging especially if lighting fittings are suspended from the conduit between fixing points. These conduits should either be of sufficient size to prevent sagging or be supported between the girders by straps of iron or steel fastened to the roof.
If the spacing of the girders is more than 10ft. apart, then it is not recommended to run conduit this way, and it should be re-routed and run on the wall or ceiling where good support can be provided. Flush Fitting Accessories Difficulty sometimes occurs when surface conduit is run to feed wall or ceiling fittings or other accessories which are fixed directly to the surface. Two methods can be used; one, to set the conduit into the wall or ceiling a short distance from the fitting and then terminate the conduit at the back; or two, to mount the fitting on a hard wooden block and run the conduit straight to the fitting.
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