# How To Check You Have The Right Cable Size

Work out which cable size to choose for your wiring job.
19 January 2021 by ​Lampfix, Brian Smith

Unsure which cable size to choose for your wiring job?

Here are some easy steps you can take to make sure!

# 1. Find out the voltage

Start off with the Voltage the fitting is operating at. 240V? 12V? 110V?

# 2. Find out the total wattage

Next, work out the total number of Watts drawn (e.g. quantity of light bulbs x their wattage).

E.g. A light with 3 arms each with a 60 watt light bulb has a total wattage of 3 x 60W = 180 Watts

Getting this info will enable you to work out the Amps drawn by the fitting in Step 3.

# 3. Calculate the current

To calculate the Current (in Amps) drawn by a fitting, divide the Power (in Watts) by the Voltage (in Volts).

E.g. using the example above, 180 Watts / 240 Volts = 0.75 Amps.

# 4. Work out the conductor size

Now you know the Current, you can work out the cable conductor size you need from the table below.  In our example, we know we need a cable rated safely above 0.75 Amps. So, for decorative lighting, 0.5mm (3A) or 0.75mm (6A) is usually sufficient.

# Current Ratings for Flexible Cables

 Conductor Size, sq mm Max Current, amp 0.50 3 0.75 6 1.00 10 1.50 15

More Examples:

## Example 1:

A mains-powered (240V) heater rated at 3000 Watts.

This draws a current of 12.5 Amps. (3000 divided by 240)

From the table above, it will need 1.5 sq mm flex.

## Example 2:

A mains-powered (240V) light bulb rated at 100W

This draws a current of 0.4 Amp (100 divided by 240)

It will need 0.5 sq mm flex.

## Example 3:

A 12V circuit of 20 LED bulbs, each rated at 3W

This draws a current of 5 Amp. [(20 multiplied by 3) divided by 12]

From the table above, it will need 0.75 sq mm flex. 