Earthing of SWA

There is an argument that a banjo can be seen. You can't tell visually how much paint there is under the contact surfaces.

That's a valid point, and does help with bad installation practice I suppose

Yep, if an inspector cannot see a banjo, it will get snagged  as its an easy visual.

Also while I've been thinking, this whole fitting of a banjo never seems to be the case with MICC cabling, assuming that as MICC requires a level of skill the assumption that the installing electrician can ensure earth continuity

If we invented the glands now, with plastic boxes and so on, banjos would not be part of the kit, but something more positive for tails to be attached like the pirahna. However, in the days when earthing was a novelty, and so folk put it on the outside so you could see it - earthed and seen to be earthed, it made sense. (and for some reason theatre lighting folk carried on doing it for much longer after everyone else had stopped.)

What should be part of the kit, and almost never is, is a nice graunchy star washer to go between the nut and the inside surface of the metal box.

It is quite possible to drill and bolt a lug through a thickly painted box and miss all contact with the metal completely if it is coated inside and out. Looks good though. Luckily most paint jobs are not that good, but some dipped plasticote finishes are. ?

My old gaffer always left the rag on a hole drilled for a gland or banjo nut "acts like a star washer"

The reason for banjos is that on a detachable gland plate on switchgear and similar, the earth continuity is assured. Furthermore, multiple banjos provide earth connections for additional cables.


Regards, UKPN

Just want to be clear I'm not trying to get out of using banjos more trying to get my head around, "it's just what you do" so it kinda begs the question if the gland plate isn't removable then is it really required, and at times when connecting up say and armoured to a socket outlet does it really need a banjo at both ends, I accept if its 2 core not really alot of choice but that in itself poses a problem if the connecting box is on the small side

I'd agree it's mostly tradition. If it was steel conduit rather than SWA but everything else the same, a banjo would be unheard of.


With plastic enclosures banjos are a pretty poor solution anyway - as the plastic can deform over time under pressure so the conventional gland-banjo-enclosure-locknut arrangement isn't satisfactory - instead having the banjo on the inside between two locknuts is recommended. All in all the proprietary 'earthing nuts' are much better solution.


   - Andy.