Category Archives: Wiring

Understanding The Outside Electricity Supply

An electricity supply to a detached garage, outdoor workshop or greenhouse requires a separate circuit of 20A or 30A current rating. The circuit can be from a fuseway in the existing consumer unit with a double-pole 30A switch fixed near the consumer unit. If there is no spare fuseway it is necessary to install a main switch and fuse unit. This can be fitted with either a cartridge fuse or an MCB.

The cable running to the outbuilding can be twin and earth PVC sheathed (2.5mm2 for a 20A supply, 4.0mm2 for a 30A supply). The outdoor section of the cable can be run overhead fixed at a height of at least 3.5m above ground level, or it can be buried underground where it must be enclosed in high impact, rigid plastic conduit buried at least 500mm below ground level.

Overhead method

In addition to the cable, materials required are: a length of galvanised steel catenary

wire (preferably stranded), a length of 2.5mm’ green/yellow PVC insulated earth cable and a cable connector; a length of 100 x 50mm timber for fixing to the outbuilding to provide the fixing height for the overhead cable fixed to the catenary wire; two eye bolts or vine eyes and an adjuster; a main switch and fuse unit to be fixed in the outbuilding in addition to the one in the house.

Installing the cable

Run the cable out of the house through a hole drilled in the wall at the specified height. Fix one eye bolt and the adjuster to the house wall, the other to the timber at the

outbuilding. Splice the catenary wire between the eye bolts and tension it, and attach the PVC sheathed cable to the catenary using cable ties. Join the earth wire to the catenary at the outbuilding end using the cable connector. Fix the PVC sheathed cable and the earth cable to the upright timber and pass the ends into the outbuilding through a hole drilled in the wall and connect the red and black wires to the L and N mains terminals of the switch and fuse unit fixed near the door.

Underground method

Dig the trench to the required depth and place a 50mm layer of builders’ sand in the bottom of the trench. Install the 25mm conduit in the trench using wide bends at the corners and pass it through a hole drilled into the house wall above the damp proof course and at the other end into the outbuilding.

Dismantle the conduit and thread in the cable. Smear adhesive bought with the conduit over the ends before fitting the elbows and coat the joints with bituminous paint.

Fill in the trench, removing any sharp stones or flints. Connect up the cable as described above. In the outbuilding, socket outlets and a fused connection unit for the fixed lighting can be supplied from a radial circuit.

How to Fit and Mend Fuses Safely

Fuses the fuses of various current rating have different physical dimensions (except the 15A and 20A which are of identical size) which prevents, say, a 5A cartridge being replaced by one of higher current rating, on 03 bath There are two types of circuit fuses, rewirable fuses containing ordinary fuse wire, and cartridge fuses. TheContinue Reading

Installing Electrical Appliances Yourself

Some appliances need to be wired direct into the domestic supply. These include items such as showers, immersion heaters and cookers. Instant showers A shower unit has an electrical loading of either 6kW or 7kW and therefore requires a circuit of 30A current rating, since the current demand is 25 or 29 amps respectively. TheContinue Reading

Fitting Electrical Sockets Securely And Safely

It is a fairly simple job to convert a single 13A socket outlet to a double. Materials required: One 13A double socket outlet. One plastic two-gang surface mounting box. A short length of green/ yellow PVC sleeving. Surface to surface conversion Turn off the main switch. Release the existing single socket from its box andContinue Reading

Fitting Electrical Switches

The modern rocker-operated 5A lighting switch is a square plateswitch containing 1, 2, or 3 switches on the one plate and has two screw holes for fixing to the lugs of a one-gang plastic shallow surface box or a metal plaster-depth flush box. Each box contains an earth terminal to which is connected the sleevedContinue Reading

Working with Cables and Plugs

Cables used for home wiring are mainly twin and earth PVC flat sheathed cables containing one red and one black PVC insulated conductor and one uninsulated earth conductor. The red conductor is used in the live pole of the circuit, the black in the neutral pole. (The black conductor is also used in the liveContinue Reading

Wiring To Plugs And Equipment

Older wiring had red insulation for the live line, black for the neutral line and green for the earth wire. Newer wires conform to a European standard. If you have a 13 amp plug with a fuse, the live wire may connect under or alongside the fuse. The neutral terminal (marked N) is at theContinue Reading

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