Flexible non-metallic conduit systems: Cable carrying capacity (wire fill)

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Flexible non-metallic conduit systems: Cable carrying capacity (wire fill)

Published: 12 October 2021 · Category: Product Catalogues & Brochures

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— T EC H N I C A L D ATA S H E E T Flexible non-metallic conduit systems Cable carrying capacity (wire fill) 40% of the cross sectional area (CSA) - UK Wiring regulations BS7671 recommend that the total cross sectional area of the sum of individual cables shall not exceed 40% of the cross sectional area of the conduit based on 'using 3 or more cables'. These instructions enable you to select the correct nominal diameter of non-metallic conduit, depending on the number and overall diameter of the cables to protect. Instructions to define the nominal diameter of a non-metallic conduit: • Step 1: Establish the number and size of each wire to be run in the conduit • Step 2: Look on the Cross Sectional Area (CSA) chart (table 1), look up the CSA taken up by each of the wires from Step 1 • Step 3: Add all the CSA values together (Total CSA) • Step 4: Look on the conduit fill value chart (table 2) and choose a conduit with a 40% fill value higher than the total CSA from Step 3 — Table 1 - Cross Sectional Area (CSA) chart Cross sectional area (CSA) [mm2] Conductor diameter Overall diameter Conductor diameter Overall diameter Example - What size of conduit to use? • Step 1: 4 x 2.5mm cables, 2 x 10mm cables, and 3 x 25mm cables • Step 2: - The CSA of Four 2.5mm cables is 19.64 (4 x 4.91) - The CSA of Two 10mm cables is 157.08 (2 x 78.54) - The CSA of Three 25mm cables is 1472.61 (3 x 490.87) • Step 3: Total of these groups is 19.64 + 402.12 + 1472.61 = 1649.33 • Step 4: Using Table 2,...