SWA, armour equivalent copper

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This is a guide to the equivalent csa copper cable to give the same resistance/impedance as the armour in various sizes of SWA cable. The importance of this is that in some cases the armour is insufficient to meet the requirements of BS 7671 table 54G, where----------. Therefore the SWA in these cases will need to be supplemented with an additional earth core such as a free core or an additional external earth cable. This is of particular concern when running an SWA sub-main to an outbuilding where it is required to maintain a TN-C-S supply.


Cross section of armour for 2,3,4 and 5 core steel armoured cables, equivalent copper is in brackets..
Nominal Conductor csa. mm sq Armour csa for 2 core (mm sq). Armour csa for 3 core (mm sq). Armour csa for 4 core (mm sq). Armour csa for 5 core (mm sq).
1.5 15 (4.82) 16 (5.15) 17 (5.46) 18 (5.79)
2.5 17 (5.46) 19 (6.11) 20 (6.43) 22 (7.08)
4.0 19 (6.11) 20 (6.43) 22 (7.08) 25 (8.04)
6.0 22 (7.08) 23 (7.40) 36 (11.58) 40 (12.87)
10 26 (8.36) 39 (12.55) 42 (13.51) 46 (14.80)
16 42 (13.51) 45 (14.48) 50 (16.08) 72 (23.16)
25 42 (13.51) 62 (19.94) 70 (22.51) 88 (28.31)
35 60 (19.30) 68 (21.87) 78 (25.09) 100 (32.17)
50 68 (21.87) 78 (25.09) 90 (28.95) 144 (46.32)
70 80 (25.73) 90 (28.95) 131 (42.14) 166 (39.40)
95 113 (36.35) 128 (41.17) 147 (47.29) -
120 125 (40.21) 141 (45.36) 206 (66.27) -
150 138 (44.39) 201 (64.66) 230 (74.00) -
185 191 (61.44) 220 (70.77) 255 (82.03) -
240 215 (69.16) 250 (80.42) 289 (92.97) -
300 235 (75.60) 269 (3.00) 319 (102.62) -
400 265 (85.24) 304 (97.79) 452 (145.40) -
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