SWA carrying two circuits?

The 314 group of regulations are to do with division of installation. What I am suggesting is that the armour of a multicore SWA covering live conductors of more than one circuit is perfectly acceptable. Think about earthed metallic conduit where the conduit forms the protective conductor. It has always been acceptable to have more than one circuit with the conduit. The multicore SWA is akin to that. Overall, 2 cables will of course give you more armour, but more expense, to my mind unnecessarily.

Thank you for the point about equivalent conductance for protective bonding conductors. I had forgotten you cannot just apply the adiabatic rules as you can for protective conductors!

Regards Bruce

Reply to
BruceB
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Is there a nuance we have missed in the wiki here?

at the end of the section on:

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say "Also note that if one is exporting the equipotential zone, that probably means the CPC of the submain is also being used as a main bonding conductor, and so it will will have to meet the minimum CSA size requirements for a main equipotential bonding conductor. Since this is often 10mm² copper equivalent, this can preclude the use of some of the smaller sizes of SWA since the copper equivalent of the armour may be too small. In these cases a separate bonding conductor can also be used."

Rather than an 8x factor we have: "Note that for ease of use of the above figures one needs to convert the actual CSA of the steel armour wires to a "copper equivalent". To do this divide the quoted figure by

2.255. So for example: a 2 core 2.5mm² cable with 70° C PVC cladding has a copper equivalent armour area of 17 / 2.255 or 7.54mm²"
Reply to
John Rumm

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Sorry - hit send too soon...

Out CSA equivalence is presumably applying only the adiabatic fault withstand requirements - which is appropriate for the original scope of providing a CPC to an outbuilding. However I get the impression we are missing a requirement here when said CPC is to also be a main bonding conductor.

Reply to
John Rumm

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> We say "Also note that if one is exporting the equipotential zone, that

Yes there is a nuance missed I think

There are 2 separate calculations or issues.

Fault currents and protective conductor sizing. Adiabatic regime applies which allows you to use ratio of 'k' values to work out minimum protective conductor size. Table 54.7 gives an example.

Protective bonding conductors. Reg 544.1 covers protective bonding conductors. 544.1.1 introduces the phrase 'affording equivalent conductance in other metals' which is then emphasised in the note at the bottom of Table

54.8. This is much more demanding and as was said in another post by Andy Wade means you need pretty large (impractically large for domestic) sizes of swa to comply if you want armour as a bonding conductor.

Regards Bruce

Reply to
BruceB

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>>> We say "Also note that if one is exporting the equipotential zone, that

Indeed - I think we have covered this angle well enough...

Yup, I think we need to create a new section on exporting equipotential bonding to cover this requirement.

Not sure how we missed that first time thought - since the same words are on the end of Table 54H in the 16th edition.

I think it might be wise to modify the tables we have that show the armour CSA to also include the resistance per m based on table H.2 in BS5467:1997

Reply to
John Rumm

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