Terminating SWA

[Harry Bloomfield]

Robin formulated on Wednesday :

In winter you can find it is too cold to actually use SWA. Some of the plastics used as the outer can become very brittle when cold.

[Harry Bloomfield]

John Woodison formulated the question :

The next stage after the nut has been put on, is to give the inner a quick sweep around following the direction of the armour strands, which helps to splay them out evenly an just enough to permit the cone to slide under the armour.

[Andy Wade]

1. It might be worth putting in some "don'ts" - i.e. saying that using a proper gland is the *only* acceptable way of terminating SWA where connection to the armouring is required, as it usually is. Specifically say that using BS 951-type earthing clamps (as used for bonding to water & gas pipes) to connect to the armour is a big no-no, ditto for taking SWA into an enclosure without the use of any form of gland.
2. It's a bit bizarre to show an SWA gland fitted to a flush mounting box. The latter will usually be embedded in masonry, but the gland (which incorporates a mechanically clamped connection of the CPC/armour) must be accessible for inspection and testing (and re-tightening if necessary). If the cable is being directly connected to a wiring accessory then a surface-mounted 'metalclad' type box would be more appropriate. (As an aside I would always mount the type of box shown the other way up, knockouts permitting. That way the earth terminal is at the top and is less likely to fill up with plaster and other crud.)
3. The banjo tag is usually used flat, the normal method of use being to drill a hole in the enclosure in line with the smaller banjo hole and use a appropriately sized screw, nut & lockwasher to give a solid earth connection. The screw can extend inside (or outside) the enclosure to create a stud for connecting crimp ring terminals, where necessary.
4. It's quite valid (IMO) not to use the banjo where the gland is used on a metal enclosure, but when doing this you must be sure that the gland itself will make a good connection. Remove paint from the enclosure where necessary and make sure the back nut is done up really tight. Any connection to the earth terminal of a wiring accessory will need a tail from the earth terminal of the box to comply with 543-02-07. Caution is also needed with enclosures which have a separate demountable gland plate. Don't rely on the plate's fixing screws to provide earth continuity.
5. For the smaller sizes (up to 10 mm^2) I find that a handy way of ringing the sheath and pre-nicking the armour wires is to use a plumber's copper pipe cutter (the rotary disc type) - try it!

There's an interesting document written by a professional electrical surveyor on the theory and practice of using SWA available on the MSN group "Sparky Heaven" -

and login required for access).

[John Rumm]

Yup, good points. Will add that.

;-) indeed, I quite agree - but it was sat on the bench in front of me when I was looking round for something with a 20mm hole in to demonstrate what it looked like fitted! (and I had just used my last surface mounting adaptable box).

OK will add that as well. Personally I like the big lock nuts that TLC do that have tapped holes in the side of them. The make a really solid fixing as they are easy to tighten, and provide an easy way to take a ring terminal terminated wire fixing.

I shall do some more photos to add next time I have a suitable box to hand. That way I can show the CPC termination more fully.

Handy tip... yup I will.

[John Rumm]

OK, have a look now, I have added words as appropriate (and pointed out that photos of a better choice of box are really needed!)

Can't get that to download in firefox... (and IE keeps wanting to register me for a MS passport!). Could you email me a copy?

Ta

[Andy Wade]

Many improvements noted. I could probably provide a photo of a cable terminated to a more suitable box, but it would have embarrassingly red and black conductors...

I'd still be inclined to take out reference to soldering to the banjo tag; I don't think anyone actually does that.

[John Rumm]

Lob it on an email, I may be able to "recalibrate" it in photoshop ;-)

(not that red and black would matter here given the purpose of the article)

I have done it on the odd occasion where you have a plastic box and not much space to play with for extra fixing hardware, like some of those external waterproof socket jobbies... (mind you, those tags are a PITA to solder to without a powerful iron to hand - so I usually use a pencil flame mini blowtorch)

[andyrdhall]

You don't mean that you... no... surely not.

Mind you TLC still has some of this contraband