Questions about swa cable and outdoor electrics

[Nabs3000]

I have moved into a new place and wish to look at the outdoor lighting circuit.

It looks like the light system is wired with swa 2 core cable to Wiska junction boxes in series however the cable only seems to be earthed at the start where it exits a outdoor rcd/mcb and plastic glands have been used which seems incorrect.

I am aware both sides of the swa cable should be earthed. There appears to be about 15 Wiska boxes. It would make sense to me that each box has the metal external sheath of the swa linked by an internal Wiska earthing plate but as it is 2 core cable how do you earn the cable/ gland plate? Do you have to use an earthing rod? If so does each Wiska box need to have a external earthing rod or just the last - this way if the wire is severed there is still continuity both sides with the earth.

Thanks

 

[sparkwright]

If it's two core SWA, the armour provides the earth, so the armour has to be connected to earth at the origin, and maintained at all junction boxes throughout the circuit.

You cannot use ordinary plastic glands on SWA because you need to earth the armour. In fact, in your case, the armour is the only means of earthing - so brass metal SWA glands are needed.

If using plastic enclosures, the earth through the armour can be maintained either by using metal banjos and a roofing nut and bolt - which is the old fashioned method and is liable to corrosion. You would connect the earth wire of whatever you are supplying to this.

***

The best and modern way to use an 'earthing nut' instead of a lock nut inside each plastic enclosure, with earth wires connected to this via a ring terminal crimp.