Bonding both sides of an swa cable

mapj1:

OK, but if the armour is not earthed at all, at the risk of stating the obvious,  the cable does not meet the regs requirement for a cable with an earthed armour, and is then to be treated as you would perhaps twin and earth, in terms of safe zones where you can route it and if it needs an RCD at the origin in case it is damaged.


Given where and how SWA is normally used,  there are few cases where electrically floating the armour makes any sense - if you do not need an earthed armour,  then use a cheaper cable. If you do need it, then earth it


I have seen the armour terminated not in glands but combed as a 'tail' into large terminal blocks, in much the same way that concentric cables are terminated at DNO fuses etc. It does not provide the mechanical anchor like  a normal gland,  but n those odd  cases where that is not needed, electrically such a termination  can be very satisfactory. (though I like to see heatshrink and there almost never is.) Certainly a tail is better than no connection.

Agree with Mike.


If buried, Regulation 522.8.10 applies even for armour of ELV cables.


Taking what Mike says a little further, also if not buried, then we need to consider whether the armour is or is not an extraneous-conductive-part.


We all know that Insulation + Sheath cables are treated as double or reinforced insulation, but what separates the armour from the live conductors? Strictly, according to the cable construction standards, it's Insulation + Filler.


As the plastic around the insulated conductors is not intended as a sheath, but a filler (the sheath being over the armour, and not under it), we must assume that the armour is an extraneous-conductive-part in LV and FELV armoured cables.


I suppose you could consider insulating the armour to avoid any contact (that would including during maintenance and testing activities), and it couldn't be terminated in an SWA gland - but that insulation would have to be done by a method that requires destruction (e.g. properly insulated using cold shrink sleeving or similar, not simply wrapping with tape).

mapj1:

OK, but if the armour is not earthed at all, at the risk of stating the obvious,  the cable does not meet the regs requirement for a cable with an earthed armour, and is then to be treated as you would perhaps twin and earth, in terms of safe zones where you can route it and if it needs an RCD at the origin in case it is damaged.


Given where and how SWA is normally used,  there are few cases where electrically floating the armour makes any sense - if you do not need an earthed armour,  then use a cheaper cable. If you do need it, then earth it


I have seen the armour terminated not in glands but combed as a 'tail' into large terminal blocks, in much the same way that concentric cables are terminated at DNO fuses etc. It does not provide the mechanical anchor like  a normal gland,  but n those odd  cases where that is not needed, electrically such a termination  can be very satisfactory. (though I like to see heatshrink and there almost never is.) Certainly a tail is better than no connection.

Agree with Mike.


If buried, Regulation 522.8.10 applies even for armour of ELV cables.


Taking what Mike says a little further, also if not buried, then we need to consider whether the armour is or is not an extraneous-conductive-part.


We all know that Insulation + Sheath cables are treated as double or reinforced insulation, but what separates the armour from the live conductors? Strictly, according to the cable construction standards, it's Insulation + Filler.


As the plastic around the insulated conductors is not intended as a sheath, but a filler (the sheath being over the armour, and not under it), we must assume that the armour is an extraneous-conductive-part in LV and FELV armoured cables.


I suppose you could consider insulating the armour to avoid any contact (that would including during maintenance and testing activities), and it couldn't be terminated in an SWA gland - but that insulation would have to be done by a method that requires destruction (e.g. properly insulated using cold shrink sleeving or similar, not simply wrapping with tape).