Planning to Rewire Your Home
Any re-, or the extension of existing wiring, should be carefully planned so as to make the job as straightforward as possible.
Use twin-socket outlets and multiple switches where possible. This will make wiring and cable routing simpler.
In bathrooms, use only pull-cord switches. This is in the interest of safety. A wall switch may be fitted for the bathroom, provided it is outside the door.
Skirted lamp holders must be used where condensation is present, such as in bathrooms or kitchens.
Rose junctions are used for both loop-in and junction box wiring. For loop-in wiring they must have four terminals.
In this case the switch wiring, the mains supply, and the bulb wiring all go directly to the rose junction. This means that all but the switch drop runs above the ceiling.
A junction box (JB) is used for joining circuits, and is useful when extending existing wiring. It provides take-off points for the next light instead of the ceiling rose. This is also used for junction box wiring in conjunction with three-terminal ceiling roses. When planning wiring, it should become apparent which circuit is most suitable.
There are several main methods of fixing cable: surface wiring, fixed with clips at short intervals: concealed wiring, through conduit tubing.
This tubing may be metal or nylon. When fitted inside metal conduit it must be earthed. The rating of cable when run through conduit is reduced. For the 6A cable it should be rated at 5A in conduit.
Cables which are to run across plaster surfaces may be concealed. This can be done by ‘chasing’ out the plaster with hammer and cold chisel to take the cable which must be conduited, unless it is a reinforced type such as Hituf. Once positioned the conduiting can be plastered over.
Cables may run freely in the roof space as long as they are slack and are resting on the roof surface or run along the sides of joists.
Wires must never be laid so that they are under tension, and in no circumstances should thev be knotted.
The plastic insulation and sheathing on cables can be attacked by some wood preservatives. This may cause an electrical insulation failure leading to fire hazard. Always check that a preservative will not affect new or existing cables.
Where cables are to be fixed to a surface, they may be secured with tinned copper or purpose-made plastic clips. Clips are available in various sizes and should be of a suitable diameter to enable easy fixing. These are fixed with brass pins or gimp pins.
Non-corroding clips must be used in damp conditions and clips of different metals should not touch each other, as this may cause electrolytic corrosion.
An example is where chrome and steel come in contact; the steel soon corrodes, as can often be seen on cars.
When fixing on brickwork, a wooden batten can be screwed to the wall, using wall-plugs. The wire is then secured to the batten with clips.
Alternatively, the wire can be fixed, using specially shaped PVC clips, with hardened steel fixing pins.
The batten need not necessarily be used on good brickwork as clips can be fixed in line with the mortar between courses.
PVC cable can be fixed at regular intervals with clips, to avoid loose sections of running cable. Plastic clips are neat and quick to use.
Bends in cables should not be less than three times the radius of the diameter.
If a shaped support is made for the bend the cable can be clipped to the support and allowed to hang freely from it. This is convenient when wiring in cavity walls.
When cables run under floorboards at right angles to the joists, holes should be drilled in the joists to route the cable. These must be fixed at a minimum of 50mm below the floorboards.
Cables running across the line of joists should never be laid in notches as these are too vulnerable in this position to accidental damage. It is better to keep holes through joists within the outer third of the joist span.
When wiring parallel with, or through joists, ensure that the fittings to be wired can be easily reached.
This presents no problem if the flooring is simple planks and an end is visible. Nails can be drawn or punched down and the end of the board simply levered up.
The boards can then be supported and raised in turn.
If no board end is free, the position of a joist can be established by seeing where boards are nailed down. A hole can be drilled in the board and a key-hole saw inserted to cut through the board beside the joist.
When the board is replaced the cut end should be supported by a timber noggin.
With tongued-and-grooved boards the tongue may have to be sawn off so that the board can be raised.
If junction boxes or other fittings have been used under floorboards, ensure that future access is possible.
Wiring a switch
Twin-with-earth cable must be used from the junction box or rose junction. The red wire goes to live (L), the black (N) to the switched side of the lamp and the green or bare to earth (E). This cable is taken to the switch through the knock-out hole in the metal switch box.
Cable should be protected from sharp edges at entry to the metal box by means of a rubber bush.
The red and black wires are connected to each side of the switch, and the earth wire is clamped to the metal box with a.
For a two-way switch, a fourth wire is necessary. Ensure that all wires are double insulated, possessing both an inner cover and a sheath. Three-core-and-earth cable can be used.
10. November 2011 by admin
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