Guide to Lighting and Power cables

Guide to single and three phase lighting and power cables

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Guide to lighting and power cables

In order for us to be able to use our lights and appliances we need to connect them to the main power supply. We will discuss the different types of cables in this post and their typical application.

The fixed wiring which runs through the walls/ceilings between the fixture and the power supply is refereed to as “cable” whereas the wire used to connect portable appliances such as lamps etc. to a wall socket is refereed to as “flex” or “flex cable”.

Cable and flex cable

Cables are flat with curved sides and have 2-4 cores within them. Flex (flexible cable) is circular with 2-3 cores within.

Electrical cable cross sectional view
Cable cross sectional view

Flex cross sectional view
Flex cross sectional view

The separated copper wires inside the cable/flex are referred to as cores. Each of the cores (except the earth core in cables) are covered in a colour coded PVC insulation which provides protection and allows easy identification. (A green and yellow insulating sleeve is pulled over the exposed earth core during the installation of the cable) The cores are then all surrounded by a final layer of PVC insulation, called a sheath, which is usually grey or white.

The colour of the cores was changed in March 2006 to align it with the requirements of the European Union. The old colours were

Red – Live
Black – Neutral

These have been replaced with the following colours

Brown – Live
Blue – Neutral

It is important to remember that you will often see a mixture of the new and old style colour coding in buildings of pre-2006 construction.

Cables come in different sizes, the size refers to the cross sectional area of the cores and this will vary depending on the amount of current flowing through them. A cable with 2.5mm2 cores is typically used for power circuits and a cable with 1mm2 cores is typically used for lighting circuits.

Single Phase Power cables

Two core and earth cable: This cable connects the consumer unit (fuse box) to the power outlet sockets and carries the electricity to appliances which are plugged in to the circuit. The cable has three cores, a live core, a neutral core and the earth core. The live and neutral cores are insulated and carry the current to and from the outlet socket. The earth or earth continuity conductor (ECC) is not insulated, except for the outer sheath, and provides a path for the current to flow to ground should a fault develop.

two core and earth cable new colours
Two core and earth cable – new colours

two core and earth cable new colours
Two core and earth cable – old colours

 

Three core flex: This type of cable is used to connect appliances such as lamps or extension cables to the power outlet sockets. The flex cable (flexible cord/cable) has three cores being Live, Earth and Neutral. Each of the cores is insulated with a layer of colour coded PVC, all three cores are then surrounded by an additional outer PVC layer known as the sheath.

Three core flex
Three core flex

 

Two core flex: This type of cable is used to connect small appliances which are double insulated and need no earth. The cable only has two cores being live and neutral. As this is flex cable it will be of circular shape with an outer sheath and two colour coded PVC insulated cores.

Two core flex
Two core flex

 Three Phase Power Cables

Three phase and neutral: typically you wouldn’t find three phase cables on domestic properties unless they are extremely large, but you will commonly find these in industrial and high rise buildings as they can supply much more power that a single phase cable. The three phase cables are usually circular and contain 4 cores with 3 of these being live and 1 being neutral. Each of the cores is covered in a colour coded PVC insulation and then grouped together and covered in a layer known as the sheath (inner sheath) this is then surrounded by a layer of twisted galvanised steel wire which has a dual purpose of providing armoured protection as well as acting as the Circuit Protective Conductor (CPC). The armoured layer is then covered in an additional layer of PVC insulation which protects the armour from rust.

Three phase and neutral cable new colour coding
Three phase and neutral cable – new colour coding

Three phase and neutral cable - old colour coding
Three phase and neutral cable – old colour coding

 

The colour of the three phase cores was changed to align it with the requirements of the European Union. The old colours were

BlackNeutral
Blue
Live (L3)
Yellow
Live (L2)
Red
– Live (L1)

These have been replaced with the following colours

BlueNeutral
Grey –
Live (L3)
Black –
Live (L2)
Brown –
Live (L1)

It is important to remember that you will often see a mixture of the new and old style colour coding in commercial and industrial buildings although there should be a warning sticker as well as phase labeling.

Lighting Cables

Three core and earth cable: This type of cable is used for wiring two way light switches. The cable consists of 4 cores with 1 being the neutral and the other three potentially being live depending on the way the lighting circuit is designed and what position the switches are in. Each of the cores (except the earth) is covered in a layer of colour coded PVC insulation to allow identification, these cores are then covered in an outer layer of PVC known as the sheath.

Three core and earth cable new colours
Three core and earth cable new colours

Three core and earth old colours
Three core and earth old colours

 

Two core flex: This type of cable is used for wiring light fittings with plastic lamp holders which do not require an earth. The cable only has two cores being live and neutral. As this is flex cable it will be of circular shape with an outer sheath and two colour coded PVC insulated cores.

Two core flex

Tools you'll need

1 COMMENT

  1. Can you show us how a single phase cabling system from the distribution board to any fixtures looks like in real life. What about double and triple phase? I don’t understand how cabling connects in real life.

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