An explanation of Cable Current Ratings
Handy information on how to work out which cable to choose in different lamp scenarios
19 January, 2021 by
An explanation of Cable Current Ratings
Lampfix, Brian Smith
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If you are rewiring a light fitting and not sure what cable to choose, start off with the Voltage the fitting is operating at and the total number of Watts that will be drawn (e.g. quantity of lamps x their wattage). This will enable you to work out the Amps drawn by the fitting and therefore the cable conductor size that will be required.

Current Ratings for Flexible Cables

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

To calculate the Current (in Amps) drawn by a particular lamp, or any other appliance, divide the Power (in Watts) by the Voltage (in Volts).

Examples:

Example 1:  A mains-powered (240V) heater rated at 3000W draws a current of 3000 divided by 240, which equals 12.5 Amp. From the table above, it will need 1.5 sq mm flex.

Example 2:  A mains-powered (240V) light bulb rated at 100W draws a current of 100 divided by 240, which equals 0.4 Amp. It will need 0.5 sq mm flex.

Example 3:  A 12V circuit of 20 LED bulbs, each rated at 3W, draws a current of 20 multiplied by 3 divided by 12, which equals 5 Amp. From the table above, it will need 0.75 sq mm flex.



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An explanation of Cable Current Ratings
Lampfix, Brian Smith
19 January, 2021
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