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.

 

[Guest112]

NO it's not to do with checking old cables, though it can be used to do so. Sheath testing is normally primarily made to New cables before final gland termination to enclosures.

Testing is performed between the SWA, to either a spike or more likely, proven earthed metalwork etc. Obviously the SWA must not be in contact with any earthed metalwork during the the testing period.

You may well have pulled in many cables in the past without undertaking sheath testing, So you'll never know if any of those cables SWA's are now corroding away or not. Any large project with project supervision, that requires work signing off before payments are released will most certainly be conducting such tests on direct buried cables.

One thing is for sure, roughly handled cables, bad pulling techniques, lack of attention to back filling procedures, and the chances are you will get a failed sheath test guaranteed!! Which is going to bad news where installations are relying on the SWA as it's primary source of earthing/CPC.

ah right so its to check for a break in the sheath and to test if the armourings are in contact with the earth meaning if it is the armours are going to rust away. now i know why id never heard of the test before all the swas we pull in are 99% of the time on ladder racking or on trays

 

[Engineer54]

ah right so its to check for a break in the sheath and to test if the armourings are in contact with the earth meaning if it is the armours are going to rust away. now i know why id never heard of the test before all the swas we pull in are 99% of the time on ladder racking or on trays

Sheath testing is primarily concerned with direct buried cables or buried ducted cables . (Many duct systems are not waterproof). Though I have known clients representatives to call for sheath testing on such installations as you describe, i guess to check for cables wedged tight against cable tray bolting/fixings etc.

 

[La Poste]

I found something out today, the lights in his garden used to work OK.
They worked for quite a while maybe two years before they started blowing the RCD.

I think this is quite encouraging because at least it shows the cable might not have been badly damaged when the new garden went on top of it.
Or maybe the cable was damaged and it has taken a while before this damage has shown itself.

If a cable has been badly damaged by damp is there some way of drying it out?

Thanks.

 

[Engineer54]

This sounds more like a buried JB(s) or joint(s) gone bad!! No you can't dry a damp cable out, (well you can, but you won't have the equipment to do that) and this cable sounds like it has more than just one problem. Your probably going to find it pretty difficult to to locate any buried joints or JB's too if nothing has been marked....

 

[La Poste]

Just a quick update to this thread.

I have just been around my neighbours house and discovered loads of buried Whiska boxes in his garden that are totally wet through.

The Whiska boxes are what the electrician used to connect the SWA supply from the house to the flex that he wired all the garden lights in, after he wired the lights he then buried these boxes, I have so far discovered three.

This is obviously what is causing his lights not to work IE RCD tripping at the board.

So for those of you that said it was underground joints that were to blame you were all spot on.

The actual SWA cables are still perfectly sound.

I won't say the nationality of the electrician that fitted all these because I don't want to be labeled a Polaphobe.

 

[oldtimer]

Well I will not label you a racist but this is the problem in this country if we criticise each other that ok but anybody else we are racist but we do have to have a grown up conversation about our lets say eastern european cousins Yarrick and Darrick who are here for a quick buck and wont be here in 5 years time so no one can find them me well I have lived in the same area for 31 years and funny enough with the same phone number.

 

[Octopus]

Just a quick update to this thread.

I have just been around my neighbours house and discovered loads of buried Whiska boxes in his garden that are totally wet through.

The Whiska boxes are what the electrician used to connect the SWA supply from the house to the flex that he wired all the garden lights in, after he wired the lights he then buried these boxes, I have so far discovered three.

This is obviously what is causing his lights not to work IE RCD tripping at the board.

So for those of you that said it was underground joints that were to blame you were all spot on.

The actual SWA cables are still perfectly sound.

I won't say the nationality of the electrician that fitted all these because I don't want to be labeled a Polaphobe.

You say this is obviously what is causing the RCD tripping but have you opened the wiska boxes yet? Could he have filled them with the "gunge"?

 

[La Poste]

You say this is obviously what is causing the RCD tripping but have you opened the wiska boxes yet? Could he have filled them with the "gunge"?

Nope.

They are not filled with anything except water, they are totally damp inside.

I've given the SWA cables a quick IR test and they all seem absolutely fine.

I shall do some more testing tomorrow when I have the daylight.

 

[Guitarist]

Have to say that I am always amazed by how some electricians think that swa is indestructible. It gets crushed and scored, kinked and trampled, then the immortal words sound out "Don't worry, it's armoured".
Agree with E54 entirely here, treat it with respect and use correct methods for burying...

 

[Engineer54]

Dry out these Wiska boxes, re-terminate all the connections within them and then fill with a good sealing gel/compound!! That should sort out any leakage problems caused by damp and/or condensation etc!!!

 

[La Poste]

To be honest I have a real phobia about underground joints and it might be an illogical phobia based on lack of experience.

I really don't like underground joints whether they are filled or not I prefer to make all my joints above ground and accessible.

I realise it might make the garden look a bit ugly with the boxes placed here and there but at least I can get to them if I need to.

I mean are these boxes filled with sealing compound really that reliable and is my phobia justified?

What are other peoples thoughts on underground junction boxes?

Thanks.

 

[Strima]

In your original post the electrician who fitted the system may not been aware of the flooding in the area and may have deemed the boxes suitable. IMHO (which is worth nothing) I would remake the junctions in boxes of IP68 rating. Another option would be to solder the terminations in the original boxes and fill with a suitable resin.

Nothing wrong with phobia but we must have confidence in modern materials, we have now moved on from hemp and bitumen.

 

[La Poste]

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.

 

[Knobhead]

we have now moved on from hemp and bitumen.

But have we improved?

View attachment 11652

 

[Strima]

But have we improved?

View attachment 11652

True, things back then were made to last.