SWA and damp.

[La Poste]

Greetings.

My neighbour has a barn that needs doing but also this.
He has just had a major extension done, a lot of work and a bit of it sub standard.
He didn't realise at the time that the guy living next door to him IE me could have probably done it better. :stuart:
Anyway he has had a lot of garden lights fitted.
A 1.5mm SWA cable runs from the house down to the bottom of his garden.
It terminates in a splash proof adaptable box and then feeds various lighting circuits.

There is a stream at the bottom of his garden and the sparky who fitted all the lights down there probably did
not realise the area was prone to flooding, I mean it gets completely submerged.
This outside circuit is wired to the fuse board inside the house and is attached to an RCD that also supplies a lot of other circuits.
Of course whenever he tries to switch his outside lights on half of his house goes dark.

I was having a look today and testing, I isolated the SWA that feeds the lights and started to measure it.
The IR results I got for L-E and N-E were about 9 Mohms but when I measured the L-N I got 0 MOhms.
I then transferred to Ohms and got a reading of 10.7 K ohms which then crept up to 20 K ohms.
You can see by my pictures.

The cable looked dry at both ends, maybe just a bit damp but I wondering why it would be that my readings are so low between L-N.
Is this just damp or has the cable been damaged in some way by all the gardening work that has gone on on top
of it.

I also went to see another guy who wanted outside lights fitted, a different customer.
He told me that his existing supply, a 2.5 SWA had a buried joint in the ground, a torpedo joint.
I measured that cable and found the IR between L-N started at 0.30 Mohms and then gradually crept up to 2.5 Mohmns.
I am not sure whether to condemn this cable and lay a new one.

So my question is really what is acceptable for SWA and how much do they vary due to damp.
Once we get a bit of juice running through them will this IR figure increase dramatically?
It's one of those areas that are grey, not black or white and maybe with a bit more experience
I could make an educated guess but right now I am not sure.

Any comments welcome.
Thanks.

 

[Engineer54]

IMHO it's the underground leakage you can't guarantee.

Especially if the cable is RCD protected and line, neutral and earth are all terminated in the same capsule and then buried.

It probably wouldn't be so bad if the cable was not RCD protected but I don't think that's a good idea in a garden with kids running around.

Underground joints and RCD's seem like a bad combination and in this instance absolutely no thought was given to changing weather and ground conditions, it worked on the day the electrician left it and then blew up at the first sign of rain and guess what the electrician was suddenly very hard to find and so was the builder.

Absolute crap wiring job.

There are underground/buried joints and boxes that have been there for literary donkey's years. Garden buried termination boxes correctly terminated and protected should last a good 30 years, if not longer undisturbed.

Your not going to get any leakage, if all the terminations are sealed/encapsulated against water ingress, condensation and damp!! Your over thinking the dangers here, there is more risk of someone putting a fork/shovel or a spike through the cable!! lol!!

 

[alli]

TLC have Pratley underground junction boxes that are made of metal and you can screw a SWA gland straight into it. I used some 4/5 years ago that where buried in a garden, I had to open one up a few weeks ago to alter the type of light. When I opened it up, it was clean, dry and looked as good as the day I first did it.

The place it is installed at have a team of gardeners that just love to smack the equipment to pieces, they say its by accident, I beg to differ. What we did do though, was dig in a plastic earth pit into the flower bed. Brought the swa into it with enough slack to be able to work on the joints above ground, then the junction box, waterproof 12volt transformer etc all live inside the earth pit. The lid goes on and with a little soil over the top as it is not allowed to be seen in this garden - jobs a good un.

The beauty of this is when the gardeners are working in that bed, their tools hit the top of the earth box and they then know to avoid it. Also if you have to do any repairs/alterations, all the kit is in one place that is easy to find.

 

[La Poste]

I found another two buried joints today so that's 5 altogether in a garden about 50 metres long by 30 metres across, is that some sort of record?

All the joints were just Whiska boxes ----ed into the ground I suppose they were quite easy to find because everywhere there is a light there is a joint between two ends of SWA 1.5mm three core and a bit of three core flex going to some recessed light which is additionally buried and also usually soaking wet inside.

So there is a sort of logic to it, anywhere there is a light there is a rubbish junction box, I think I'm getting the hang of this.

I like the idea of an earth pit enclosure to terminate stuff in, you can always get to it and you know where it is.

 

[oldtimer]

Remember all these things cost unless you are doing for Hee Haw so you may have either run a new swa looping in and out of the lights or as suggested new boxes with resin

 

[La Poste]

There's only really one joint box that needs burying and it is right in the middle of the garden, all the others are round the edges and can be made safely above ground and hidden behind bushes etc.

The actual cables are fine, R1R2 right to the end of the garden from the house is just below 1 Ohm and they IR test OK, at least he used nice cables.

I like the sound of an earth pit and then use resin sealed joints, leave myself plenty of slack in the box just in case, the best of both worlds.

The rest of the house is not much better, the quality of workmanship is cr@p.

 

[Knobhead]

If flex is used from the joint avoid compound. You can guarantee as soon as it’s set someone will put a spade through it.

You say the cable tests OK, have you tested the sheath for damage?

 

[La Poste]

A sheath test is something I haven't done, my evenings reading has just been booked up.

Thanks Tony.

 

[Knobhead]

An IR test on the sheath between the armours and earth. It will show up any damage to the outer sheath, it’s a pain in the arse to carry out in an existing installation, but worth it to forewarn of future problems.

As for flex and solid compound how do you change a damaged flex?

 

[La Poste]

Well it's only the one joint that will be buried and resin sealed so I guess what I will do is seal the SWA joint with a very small amount of flex, leave some spare flex trailing, this will all be inside the earth pit.

From this flex that is trailing inside the earth pit use a waterproof or underwater joint box to connect to the lamp, if this lamp flex is damaged I can easily change it.

AS long as I leave plenty of spare cable I should be alright, either this or insist that the whole lot is joined above ground and use no resin at all.

 

[Knobhead]

Wasn’t having a go at you La Poste. Just trying to avert future problems for you.

It just made me remember some one doing it at work and muggings (me) had to chop a section out of the SWA and put a through and a breach joints within 3’ of each other.

 

[La Poste]

No worries Tony I never thought you were having a go.

I also like to try to think of any eventuality, there's nothing worse than doing something and then having to return to put it right.

 

[La Poste]

There are these that don't need sealing compound but I have never tried them:



Adding the flex could be an issue but maybe I could re-wire the lights in SWA also.

 

[Knobhead]

Used them in the cement industry. They were supposed to be above ground but it’s funny how the ground level changes with the amount fallout from the process. It’s a wonder the plant didn’t vanish under it. The boxes most have been a good 2’ under ground.
This picture will give an idea of what the fallout was like.
View attachment 11734

 

[La Poste]

It sounds like they did their job very well.

So there are basically three types of waterproof joint boxes, the Pratleys as shown above, the resin sealed boxes and those little waterproof plastic joint connectors used in fish ponds and the like.



I'll have a little read about them.

 

[Octopus]

Anyone (old enough) to remember the Blue Peter "time capsule"?

Buried in the late 1960's and dug up in the year 2000?????

Everything in it was completely ruined!

Pratley boxes for me or Wiska with the gel if it has to go underground!