Bonding SWA armour wires

[rick]

A practical Q

Will have 6mm 3 core SWA terminating on an insulated IP65 box, using CW20 gland

I will also be bringing in (via flexy conduit and waterproof gland) a

16mm single core earth lead from a local earth rod.

(earth will be insulated and in flexible conduit hence 16mm)

This cable can terminate on to terminals in the box, what size cable do I need to bond to the armour wires, my understanding is 6mm is correct size … and could best be achieved with a Piranaha nut. Any advice/comments.

[John J]

If the gland kit contains a brass earth tag I'd drill through the smaller hole and enclosure, employ a brass nut and bolt through both. Then crimp a suitable lug onto the end of the cable and secure it to the brass bolt no need to fanny about with fancy fixings.

[John Rumm]

From the point of viw of providing an adequate earth (i.e. not exporting an equipotential zone), 6mm^2 will be more than adequate (if you think about it a 6mm^2 T&E only has a 2.5mm^2 earth).

Yup, it is what I normally do - crimp an eye terminal on the end of the wire, and bolt onto the side of the nut. However it can be a bit tight on space in those boxes when you need several such connections.

An alternative is to use the banjo tag that comes with the gland. You can either bend its tab up and bole the eyelet on the wire to it in the box, or sometimes it is neater to leave it flat, and drill a hole through the box wall inline with its hole. Then stick a dome head bolt through the outside of the box, through the banjo, through the eyelet on the wire, and stick a nut on the inside. That gives a good rigid fixing that is also flush with the inside of the box.

[rick]

ce in those boxes when you need several such connections.

I'll try a Piranha nut .... don't want to drill a hole for nut & bolt as this is external and could compromise IP65 rating, used Non-metal boxes for this reason.

[John Rumm]

You can bend the tag on the banjo if you want it all inside the box:

[John Rumm]

I have tweaked the main terminating SWA article with some more details on ways of terminating the earth and armour.

[ARW]

For a one off I would suggest the Piranha nut. If you are doing hundreds a year like myself then it's bend or drill.

[Fredxx]

Nice article.

I've struggled to see why Piranha nuts are so expensive and the standard galvanised nuts are so thin!

[ARW]

Milking it for all it's worth.

[John J]

[John J]

You don't consider the cable gland hole through the box is different in some way to the small hole for the brass bolt?

[John Rumm]

The standard ones are the cheapest thing that will still do the job, and the Piranha nuts are priced at the highest level they can get away with where people will still buy them because of the extra convenience and time saved when fitting.

[Fredxx]

The Piranha nuts are subject to patent that seemingly has a few years still to run:

Though it not obvious when it runs out?

[Robin]

UK patents last up to 20 years from when filed so (without checking the details) looks like 2025

[Andy Burns]

If using wiska boxes, and having multiple SWA cables terminating into the box, they do earth bars, which work as a "double" piranha nut for the same sort of price.

[Fredxx]

I wasn't sure if it would be based on filing date, which is 2004?

[Robin]

Patent law not my thing but I thought the 20 year period ran from the filing date (in 2005) rather than from the priority date (in 2004), and at least some others who claim to know more seem to agree.

[John Rumm]

Nice - not seen those before.

(I added a link and some words to the wiki page)

[Fredxx]

Thanks, I wasn't sure. I believe the priority date only gets invoked if a third party submits a competing patent after the priority date, but before the filing date.

TBH, after re-checking the Piranha nuts are a little over £2 each, so for a professional, if it saves then a couple of minutes or more I would have though it's a no-brainer.

[John Rumm]

Depends on if you are being paid by the hour, or a fixed price for the job :-)