How To Check You Have The Right Cable Size
Work out which cable size to choose for your wiring job.
19 January, 2021 by
How To Check You Have The Right Cable Size
​, 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). 

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).



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.



Current Ratings for Flexible Cables


Conductor Size, sq mm
Max Current, amp
0.503
0.756
1.0010
1.5015




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.



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How To Check You Have The Right Cable Size
​, Brian Smith 19 January, 2021
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