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How To Measure Electric Cable Size?

An essential part of any building design is determining the right size and type of cable to install for each electrical circuit. The wrong electrical cable size can be wasteful, and in some cases dangerous.

Cables with different thicknesses are used to cope with different amounts of electrical resistance. So, electric cookers, showers, and heaters need thicker cables as they use a large amount of current. And the greater the distance the current has to flow the greater the resistance and the less current available as a result.

Cables placed under insulation and in insulated walls will carry a different rating. And electric cable sizes vary depending on the job they need to do. See how to measure cable size here…

Types of electrical cables

Understanding Basic Terms

An electrical cable is a set of wires that supply electricity to homes and businesses. Cables supply your meter box, sockets, ceilings and wall lights. Most household cables have a blue wire which is neutral, a brown wire for live current, and a bare wire to earth the residual current. This cable is known as a two core and earth, or twin and earth.

An alternative cable used for domestic lighting is called a three core and earth. The extra wire here is used an additional conductor to carry more power between two or more switches operating the lights in an insulating sheath.

Appliance flex in simple terms is a flexible cable. They’re used for appliances that need to be moved around a lot – where a fixed cable would be unsuitable as it may get damaged or crack.

Resistance is electrical fiction where the wires in the cable or flex absorb some of the current energy meaning less arrives at the target destination than was originally sent.

An amp is the base unit of electric current that calculates the electromagnetic force between electric conductors carrying the electric current.

Cable Selection

You need to make sure that your cable has the sufficient current rating for the expected circuit load including a safety margin. The run length of the cable won’t cause a voltage drop of more than 3%, and the properties of the cable are suitable for the installation.

Cables for lighting circuits for domestic purposes are usually a 1.5mm cable. And cables for sockets on a ring or radial main are normally a 2.5mm cable. This measurement is the cross-sectional area of the individual wires within the cable – the actual area of the exposed face of the wire.

The size of the cable should be printed on the sheath. The cross-sectional area of the earth wire in a 1.5mm cable is 1mm. In a 2.5mm cable, the measurement is 1.5mm.

Electric Cable Sizing

Cable sizes with their current ratings are shown in this table below for cables enclosed in an insulated wall:

Cable SizeCurrent Rating(Amps)

Electrical cable size chart amps with reference to plasterboard ceilings or joists covered by thermal insulation less than 100mm are shown below:

Cable SizeCurrent Rating(Amps)

For cables that are installed with the clipped direct method the following electrical cable sizes chart applies:

Cable SizeCurrent Rating(Amps)

Electrical cable sizes for that above exceeding 100mm are:

Cable SizeCurrent Rating(Amps)

Cable Construction

The materials used to construct cables vary and include:

  • PVC – widely used in electrical cable construction for insulation, bedding, and sheathing due to the simplicity of its processing
  • Thin wall – a harder grade of PVC cable with better electrical insulation properties. It’s light and has a greater working temperature range making it more resistant to abrasion and offering more protection.
  • Tinned copper – extensively used in marine environments where long-term good conductivity is necessary
  • Double insulated cable – this cable had thin inner insulation and an outside thicker layer to protect the conductor – most often used in agricultural and heavy plant machinery

Speak to a Qualified Professional

What cable do I need? This frequently asked question will be simply answered by your trusted local emergency electrician. When you need to know anything about electrical work, re-wiring, or new installation you’ll get all the necessary help and advice – from qualified and registered electricians.