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RCD & cable mechanical protection

Apostolos
Good morning everyone.

I have couple of questions for the more experienced.

1) In order to get away from an RCD (assuming that the circuit does not feed a socket...) you need mechanical protection for cables chased in the wall at less than 50mm.

Does this mechanical protection need to be earthed as well if we assume that the cables will be protected by galvanized steel conduit???

Or just the steel conduit is enough?

2) I know that a SWA cable is considered mechanical protected by the SWA. Does the SWA need to be earthed? What if I use an external CPC and do not connect the SWA to earth. I guess this is the same question as question number #1...

3) I have a cable from PRYSMIAN called AFUMEX LSX BS8436 and in the description it states:

    "Independently assessed by ERA for nail penetration tests (1.5mm2 to 2.5mm2)"

     Does this make this cable mechanically protected like a SWA cable? Do I understand it correctly?

.....

Thanks for your time guys

Kind Regards

Apostolos
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  • 0

    In order to get away from an RCD (assuming that the circuit does not feed a socket...) you need mechanical protection for cables chased in the wall at less than 50mm.



    There are two different approaches - either earthed protection (i.e. where the live conductors are surrounded by something that can act as a c.p.c.) and mechanical protection (which is purely mechanical and so doesn't require any earthing).


    Earthed steel conduit/trunking, armoured cables, BS 8436 cables etc all normally fall into the first (earthed) category (reg 522.6.204 options (i) to (iii)), not mechanical protection.


    Mechanical protection is reg 522.6.204 option (iv). In these days of nail guns etc it's very difficult to be sure that mechanical protection can work reliably. Some offer "safe plates" for protecting cables/pipes passing through joists/studs - but as far as I'm aware there's nothing official to say they're adequare or acceptable to BS 7671. In some limited circumstances (e.g. where site procedures or H&S rules would prevent the use of power tools) then perhaps mechnical protection could be justified - but in general the safest option is to go down the 'earthed' route.


       - Andy.
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  • 0

    In order to get away from an RCD (assuming that the circuit does not feed a socket...) you need mechanical protection for cables chased in the wall at less than 50mm.



    There are two different approaches - either earthed protection (i.e. where the live conductors are surrounded by something that can act as a c.p.c.) and mechanical protection (which is purely mechanical and so doesn't require any earthing).


    Earthed steel conduit/trunking, armoured cables, BS 8436 cables etc all normally fall into the first (earthed) category (reg 522.6.204 options (i) to (iii)), not mechanical protection.


    Mechanical protection is reg 522.6.204 option (iv). In these days of nail guns etc it's very difficult to be sure that mechanical protection can work reliably. Some offer "safe plates" for protecting cables/pipes passing through joists/studs - but as far as I'm aware there's nothing official to say they're adequare or acceptable to BS 7671. In some limited circumstances (e.g. where site procedures or H&S rules would prevent the use of power tools) then perhaps mechnical protection could be justified - but in general the safest option is to go down the 'earthed' route.


       - Andy.
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