Components used in electrical installations

Incoming supply

Suppliers fuse

Meter

Consumer unit

Appliances/circuits

After the supply leaves the consumer unit, it goes to the appliances/circuits. To get there it travels along cable and flex, these are a combination of conductors and insulators. The conductors allow electricity to flow (electrons). Good conductors are as follows; copper, silver and aluminum. Rubber, plastic and glass are good insulators.

Typical cable

Sizes of cable

1.5mm twin and earth = lighting

2.5mm twin and earth = ring main

6mm twin and earth = smaller electric shower (7kW)

10mm twin and earth = larger electric showers (11kW)

Flex

Used for extension cables and leads for appliances above floor level. With flex, the earth is insulated. The correct selection of flex is important to prevent overheating (cross sectional area).

Heat resistant flex

Used on heat producing appliances; kettles, irons and immersion heaters.

This flex can be heated up to 850C without being damaged or going brittle.

Immersion heater needs to be controlled by a double pole switch. Which must be fitted within 1.5m of the heater, wired using heat resistant cable.

Protection

Trunking

The main purposes of this are to:

Protect flexes from damage
Protect the customer from the flexes
Support the flexes.

Conduit

The main purpose of this is to:

Protect the flex from damage
Protect the customer from flexes
Support the flex.

Remember conduit can be surface mounted or concealed as can trunking, hiding the wiring so be careful...Always use an approved detector.

Electrical supply terminology

Power triangle used to work out Watts, Amps and Volts

Used to work out Volts, Current and Resistance

Domestic 3 pin plug

Modern appliances come with a moulded plug for safety, which offers access to the fuse. Re-wireable plugs are also available with cartridge fuses. Maximum fuse size is 13 amp

Sockets

A video explaining a ring main, which shows a wall socket, which is flush mounted. There are other types of socket such as;

Flush mounted
Surface mounted
Switched
Un-switched
Single socket
Double socket

Images of single gang flush mounted back box

Installing the back box for a flush mounted socket.

Dry lining double back box

Single surface mounted

Switches

Two way switch: allows the live to be switched off in two different places (eg upstairs and downstairs).

One way switch: allows the live to be switched off in one place (eg for a single room).

The switches can be;

Flush mounted
Surface mounted
Single gang
Multi gang

Fused spur

Flush mounted
Surface mounted
Switched
Un-switched
Luminated

A Fused Spur Switch is commonly used for powerful electrical appliances, such as washing machines and dish washers that need to be installed without a plug; they are also used for electrical items that need to be installed on a separate cable from the ring main, for safety and maintenance purposes

Junction box

No conductors must be visible when connected to the junction box. On central heating systems the lafge junction box is used. The wiring centre.

Pre- wired lighting spur junction box

Heavy duty junction box

Wiring centre

Pull cords for danger zones

Lights in a bathroom – single pole isolator
Isolator for electric shower – double pole isolator (these
must be luminated and have a manual indicator).

Isolators

The on and off switches are not isolators, all isolators need to be locked off and labelled such as; the main consumer unit isolator each MCB and fused spur.

Electrical timers

On the whole most timers will be installed on a central heating system such as a programmer or a time clock.

Time clock

Programmer

A variety of different programmers are available and which one is best for you will depend on what type of heating system you have, and how you use it.

Test yourself

Terminals

Crimp terminal

Terminal connector strip

Pillar terminal

Brass claw terminal fixings

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