To calculate the conduit size you require, you must first multiply the cross-sectional area of each cable by the appropriate factor, the total factor for each of your cables must not exceed the capacity factor recommended for each conduit diameter.
Conduit Diameter (mm) Capacity Factor
· 16mm 290
· 20mm 460
· 25mm 800
· 32mm 1400
The recommended maximum fill percentage of a conduit containing just 1 wire is 53%, for 2 wires, the maximum percentage is 31% and if the conduit contains 3 or wires, the maximum percentage is 40%. The size of the conduit you require can all be checked by calculating the cross-sectional area of the wires that will be contained within the conduit.
When incorporating bends within the conduit, it is recommended that 15% is subtracted from the maximum cross-sectional area being used. You should also avoid using 2 or more 90° bends in a single section of conduit.