Flexible metallic conduit systems

ADAPTAFLEX® FLEXIBLE METALLIC CONDUIT SYSTEMS

— Technical section 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 metallic conduit, depending on the number and overall diameter of the cables to protect. Instructions to define the nominal diameter of a 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

Example - What size of conduit to use? • Step 1: 4 x 2.5mm cables, 2 x 10mm cables, and 6 x 6mm cables • Step 2: - The CSA of Four 2.5mm cables is 19.64 (4 x 4.91) - The CSA of Three 10mm cables is 235.62 (3 x 78.54) - The CSA of Six 6mm cables is 169.62 (6 x 28.27) • Step 3: Total of these groups is 19.64 + 235.62 + 169.62 = 424.88 • Step 4: Using Table 2, we chose the size of metallic conduit with 40% fill value higher than 424.88: 50mm NOTE: The information given above relates to SPL liquidtight conduit in combination with M-Type fittings.It is given in good faith and should be used only as a guide in conjunction with the relevant wiring regulations.

— Table 2 - Wire fill of metallic conduit

— Table 1 - Cross Sectional Area (CSA) chart

Nominal diameter (mm)

100% fill value

40% fill value

Overall Diameter [mm]

Cross sectional area (CSA) [mm 2 ]

CSA [mm 2 ]

12 16 20 25 32 40 50 63 75

25.5 83.3

10.2 33.3 64.2 97.3

0.79 1.77 4.91

160.6 243.3 452.4 855.3

1.5 2.5

181

4 6

12.57 28.27 78.54

342.1 465.7 785.4

1164.2 1963.5 3473.3

10 16 25 35 50

201.06 490.87 962.11 1963.50

Conductor diameter

1389.3

Overall diameter