SWA Armouring CSA Sizes Chart

by Editor on October 27, 2018

Use this chart to find the CSA cross sectional area of SWA steel wire armoured cables. It also shows the gland sizes.

A chart showing SWA armouring CSA and cable gland sizes.

(Click the table to enlarge)

These dimensions should be used for guidance only as steel wire sizes can vary between manufacturers.

Rule of thumb is – Always run a cable with integral earth core or install a separate parallel earth cable.

SWA armoured BS6121 CW cable gland showing steel armouring earth ring

Using SWA steel wire armouring for earth cpc conductor

The steel wire sheath of an SWA cable can be used as an earth conductor if the cross sectional area of the steel wire is sufficiently compliant.

Note – Steel does not conduct as well as copper. It has a higher resistance, therefore cannot be compared size for size with copper.

Caution

It’s not only about the size (cross sectional area) of the earth conductor. Here are some important factors to take into account when sizing the steel armouring of an SWA cable for use as a cpc earth conductor. All of which need to be taken into account in calculations:

  • Steel has a higher resistance than copper, therefore needs to be of a greater cross-sectional area to achieve the same result. Calculations should include values of k from Table 54.5 .
  • Steel armouring must be clamped tight at each end using the correct cable glands. Corrosion over time may affect the effectiveness of an earth connection.
  • May not be suitable for PME installation where exposed conductive parts is not allowed outside the equipotential zone.
  • Where the earth conductor is common to several circuits, its cross-sectional area should be based on the largest line conductor of those circuits.

Consult Regulation 543.1.1 to 543.1.4 and Table 54.7 of the current IET wiring regulations.

Use Calculations

Regulation 543.1.1 states that the cross sectional area of every protective conductor, other than an bonding conductor, should be:

1. Calculated in accordance with Regulation 543.1.3, or
2. Selected in accordance with Regulation 543.1.4 (Table 54.7)

By Calculation Using Method 1– If the SWA armouring is to be used as a protective conductor (cpc) it would need to be sized by using the appropriate value of k and the adiabatic equation in 543.1.3 .

By Table Using Method 2- Regulation 543.1.4 states that you can use Table 54.7 to determine the required cross-sectional area of a protective conductor.

Check Table 54.7 for yourself to determine the size of earth conductor required because you’ll still need to do a calculation where the cpc is a different material (ie. steel) from the line conductor (ie. copper).

You can find the cross-sectional are of the armouring of various SWA cables detailed in Tables D9,D10A and D10B of the Guidance Notes 1 IEE publication.

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