Electricity in the Home: Installing Ring Mains
Power can be used indoors and outdoors. The modern ring-main circuit distributes the load on an electrical circuit at any one time. For the average household, two circuits provide a convenient arrangement. Outdoor lighting and power can serve garage or greenhouse, as well as garden lighting and pumps for garden pools.
For an outdoor light, such as a porch, wire to any fitting on the house wall should consist of 1.0mm2, twin-with-earth cable. The earth, neutral and live points should be connected up at a convenient junction box or ceiling rose.
While in older circuits there may be no earth wire, the outside lamp must be earthed, and a separate earth continuity conductor may be used.
The lamp fitting should be a fully weatherproof type if it is to be in an exposed position. If so, it must be enclosed in a globe which seals on to a rubber gasket. The neutral and live are taken to the bulb holder, in the normal way, and the lamp frame is earthed.
A grade of cable with an approved plastic insulated covering, such as PVC, PCP or CSP, must be used for outdoor wiring.
Non-corrosive cable clips should be used. If possible, avoid clipping cables to render or similar surfaces. Wiring to aor shed may be routed underground or overhead.
Cables should not be run along fencing or railings.
The cable may be run in conduit or suspended from a wire which takes its weight.
Heights should be 5.2m above the ground if any vehicles pass beneath, 3.5m for suspended wiring and 3.0m for conduit wiring.
Conduit can be used for spans of up to 30m; for longer spans a supporting wire should be used.
Holes should be replugged with mortar to minimize the risk of fire spreading and to keep out rain. Similarly, where wire emerges from the conduit, if outside, this should be plugged with a proprietary weather-proof sealing compound.
Where a supporting wire is to be used, it should be ‘strained’ between strong fixing points, The cable is then fixed by clips to the wire. Clips can be spaced at 460mm centres. In this way no strain is imposed on the cable.
Where cables are led round at angles, the inner radius must be at least eight times the cable diameter.
Underground wiring is often more convenient when wiring a greenhouse or an outhouse some distance from the main building. Mineral-insulated copper-covered cable, Hituf cable or armoured cable are generally used, though PVC is suitable in many cases.
The cable should be laid in a trench 500mm deep so that it will not be disturbed when digging. The soil that covers it should be free from flints. To make sure of this, the first 75mm depth of soil cover should be sifted to remove all the stones. Cable should have a protective cover of stout tiles or be run buried in galvanized-steel conduit.
The supply must not connect directly to the mains in the house but must go through its own switched fuse box. This is because you must be able to isolate external circuits independently of the house circuits.
The use of 4.0mm2 cable is advisable on long runs carrying high loads, to minimize voltage drop. A 2.5mm rating can be used if loadings are only to be small.
In the greenhouse the cable must be connected to a mains switch and fuse unit, mounted about l.5m above the ground. Greenhouse and garden circuits can be wired from this.
For outhouses and garages a ring circuit can be used.
10. November 2011 by admin
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