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Topic Title: SWA earthing problem
Topic Summary: Bad connection
Created On: 18 February 2014 08:52 PM
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 18 February 2014 08:52 PM
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mossep

Posts: 330
Joined: 05 December 2010

SWA earthing problem

Ive got a job to try and rectify where the SWA is not giving good earth loop reading to the dis pillar it feeds.

So you get an idea of the scenario, the Zs at the panel board is 0.08, the Zs on the brass gland where the SWA terminates in a remote dis pillar is 0.20, the Zs measured inside the dis pillar is 1.98. This seems to be down to a corroded locking nut.

The SWA is a 70mm 4c, and its coming into the bottom of an out door dis pillar in a caravan park. As you can appreciate, removing the SWA from the dis pillar will be quite a long and painful job, involving digging up the ground and stripping down the whole board.

Im toying with putting a clamp around the SWA before is enters the board and running and large earth from the clamp into the board. Is there anything on the market that can be used, I did think of a large corrosion proof Tenby, but Im not sure how it would stand up to high fault currents if something were to go wrong. The other thing I considered were constant force springs, like you get in underground joint kits.

Anyone on here got any suggestions other than pull the cable out and re-terminate it?

Thanks

Martin

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 18 February 2014 09:20 PM
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slittle

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Is the banjo bolted and lugged back to the earth terminal or is it relying on the metal/metal (with paint or rust in between contact) between the lock nut and the enclosure ?

If I was going for a clamp, I'd go constant pressure spring and then loads of self amalg tape over it to keep the weather out


Stu
 18 February 2014 09:48 PM
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mossep

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The dis pillar is GRP construction, with a large brass plate in its base. This brass gland plate has an earth wire lugged to it going to the main earthing bar. The problem is there is very poor continuity between the brass plate and the main incoming SWA gland.

Would a constant force spring hold say a 35 or 50mm single earth tight against the SWA, or would flexible cable be better? The straps you get in underground joint kits are flat braided section so look like they have a better contact area.

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 18 February 2014 09:53 PM
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daveparry1

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I think i'd try a bs951 on the actual gland nut (as the Zs is ok there) and then an earth lead from there into the box. This situation is the very reason that I rarely use the armour for the cpc!
 18 February 2014 11:10 PM
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anastasis

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I don't really understand what the issue is - if you can get to the armour, surely you could replace the locknut. The SWA gland itself is probably OK. Removing the cores from the DB to do the locknut can't be that difficult, even if they are 70mm.

But here's an idea... assuming you can undo the locknut and there's enough male thread from the gland sticking out through the brass plate, you could put a piranha earth nut on this thread and connect an earth lead to that. The nut has grubscrews which lock it onto the thread, so it wouldn't matter about bad continuity between the gland the brass plate.

The gland is probably 40mm, and the 40mm earth nut has an M10 stud on it so can easily take a crimp lug for an suitably large earth lead.
 19 February 2014 06:53 AM
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Fm

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Put a new gland
Removeable gland plate at the pillar?
If not create one?
Earth clamps are for pipes not cables, its non compliantnand rough as
What about a piranaha nut?
 19 February 2014 09:55 AM
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daveparry1

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If you read what I said FM you'll see I didn't suggest putting a clamp on the actual cable, I said put it on the gland! The brass gland is quite capable of coping with the pressure of a bs951. As for rough, maybe not conventional but maybe a way around the OP's problem.

Thinking "outside the box" comes to mind here, something many electricians seem to have problems doing!
 19 February 2014 03:56 PM
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mawry

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Have a lookm on the Furse website, under earthing, bonding and lightning protection. There may be a clamp you can use on there. Not sure it would be following manufacturers instructions tho.
 19 February 2014 04:57 PM
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TVRBryan

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Apologies if I've got the wrong end of the stick but when earthing an outside feeder pillar, aren't you supposed to earth the SWA armour from the origin/source & not earth the SWA at the pillar end, as an earth rod should be used as an earth at the outside pillar end (separated from the SWA armour/earthing)?
 19 February 2014 05:21 PM
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anastasis

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Originally posted by: TVRBryan

Apologies if I've got the wrong end of the stick but when earthing an outside feeder pillar, aren't you supposed to earth the SWA armour from the origin/source & not earth the SWA at the pillar end, as an earth rod should be used as an earth at the outside pillar end (separated from the SWA armour/earthing)?


That's if you're converting to TT earthing, which probably isn't the case here.

Given that this pillar is fed with 70mm cable, I reckon it feeds a lot of final distribution pillars. The TT conversion is probably done at those.
 19 February 2014 07:24 PM
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mossep

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Originally posted by: anastasis

Originally posted by: TVRBryan



Apologies if I've got the wrong end of the stick but when earthing an outside feeder pillar, aren't you supposed to earth the SWA armour from the origin/source & not earth the SWA at the pillar end, as an earth rod should be used as an earth at the outside pillar end (separated from the SWA armour/earthing)?



That's if you're converting to TT earthing, which probably isn't the case here.



Given that this pillar is fed with 70mm cable, I reckon it feeds a lot of final distribution pillars. The TT conversion is probably done at those.


The TT is carried out at the individual pitch supplies.

The dis pillar feed groups of 3 pitch supplies, around 30 in total.

As for the piranha nut idea, I didn't know they went any bigger than 25mm, I'll have a look into that and make a recommendation.

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 19 February 2014 07:58 PM
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peteTLM

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http://www.s-w-a.co.uk/resourc...nd-Accessories/055.pdf

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Lack of planning on your part doesn't make it an emergency on mine....

Every man has to know his limitations- Dirty Harry
 19 February 2014 08:14 PM
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Fm

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Answer from hawke glands when i asked can i put a clamp on the gland
Haha
 21 February 2014 06:29 PM
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weirdbeard

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Originally posted by: mossep

This seems to be down to a corroded locking nut.




Anyone on here got any suggestions other than pull the cable out and re-terminate it?



Hi martin, from the sounds of it my first attempt to improve things would be loosen off the lock nut as far as possible without disconnecting, then set about de-corroding the locknut and the gland plate with emery cloth/possibly dremel type rotary tool, a liberal dousing with WD40 - an hour tops? See how it goes when reconnected, after that look at ways of preventing the problem from happening again (a squirt of WD40 once or twice a year should suffice? )
 24 February 2014 01:20 PM
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AJJewsbury

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I'm puzzled - if you've got a brass gland onto a brass plate, why is corrosion of the lock-nut causing a problem? Could it just be loose?
- Andy.
 06 March 2014 08:48 PM
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weirdbeard

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Hi martin, what was the outcome?
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