Bonding both sides of an swa cable

Why’s it not classed as bonding sorry I’m just confused. I know if I used the armour as a cpc it would be earthing

The armour would be classed as an exposed-conductive-part (just like the metal case of a class I appliance) - so the protective conductor connecting it to the means of Earthing would be a c.p.c - since it may have to carry the full earth fault current until the protective device opened to provide ADS. That would still be the case if the armour didn't form the c.p.c. for the downstream circuit as there could still be earth faults either within the cable (if damaged) or at the far end (say to the gland if it wasn't separately earthed at the far end).


Supplementary bonding is a different kettle of fish where you're connecting together exposed-conductive-parts that are already connected to their appropriate c.p.c.s or extraneous-conductive-parts (which if entering from outside of the installation would already be main bonded) - so even in the worst case they'd only be carrying a portion of the earth fault current as they're in parallel with the appropriate c.p.c.. The idea of supplementary bonding is to reduce the voltage difference between simultaneously accessible parts within a small area (such as a bathroom) - not to provide basic earthing to any one part.


As you've noticed that OSG table only works for situations where the associated c.p.c. is 6mm² or less - other situations (e.g. larger cables) might well demand larger supplementary bonding conductors. In general when connecting two exposed-conductive-parts the supplementary bonding conductor would have to be at least the same size as the smaller of the c.p.c.s (always subject to the 4mm² or 2.5mm² minimums for any separate protective conductor for mechanical robustness reasons).


   - Andy.

Why’s it not classed as bonding sorry I’m just confused. I know if I used the armour as a cpc it would be earthing

The armour would be classed as an exposed-conductive-part (just like the metal case of a class I appliance) - so the protective conductor connecting it to the means of Earthing would be a c.p.c - since it may have to carry the full earth fault current until the protective device opened to provide ADS. That would still be the case if the armour didn't form the c.p.c. for the downstream circuit as there could still be earth faults either within the cable (if damaged) or at the far end (say to the gland if it wasn't separately earthed at the far end).


Supplementary bonding is a different kettle of fish where you're connecting together exposed-conductive-parts that are already connected to their appropriate c.p.c.s or extraneous-conductive-parts (which if entering from outside of the installation would already be main bonded) - so even in the worst case they'd only be carrying a portion of the earth fault current as they're in parallel with the appropriate c.p.c.. The idea of supplementary bonding is to reduce the voltage difference between simultaneously accessible parts within a small area (such as a bathroom) - not to provide basic earthing to any one part.


As you've noticed that OSG table only works for situations where the associated c.p.c. is 6mm² or less - other situations (e.g. larger cables) might well demand larger supplementary bonding conductors. In general when connecting two exposed-conductive-parts the supplementary bonding conductor would have to be at least the same size as the smaller of the c.p.c.s (always subject to the 4mm² or 2.5mm² minimums for any separate protective conductor for mechanical robustness reasons).


   - Andy.