SWA failure.

[defadog]

Sitting right next to a leaking watermain...which has been leaking for months based on the ground I was digging out.

Howver, given that the garage (left hand spur) remains sound, how do I tell if this really is the problem...or do you agree based on its condition it almost certainly is?

 

[bernardgreen]

or do you agree based on its condition it almost certainly is?

I agree

 

[defadog]

Thought you might say that. I am not happy with how shallow it is..nor that it runs under a retaing wall. Would it be better for me to fit a junction box on the retaining wall on the right ( there is plenty of loop on the cables) so that it is obvious there are cables there ? It also dets it clear of the water main.

 

[defadog]

Also..the house is a PME fit, and currently the earth is exported to both garage and shed...about 100m away as the cable runs via the protective mesh. Would I do better to breat the earth and fit new earths at each?

 

[bernardgreen]

To me it looks like the seals have failed and the box has been flooded.

Inside the box there could be quantities of rust from corroded steel. This would be conductive and could explain the voltages on low impedance that you measured.

I would seriously look at replacing the entire cable as the amount ( length ) of corrosion of the SWA is un-known

 

[conny]

To me it looks like the seals have failed and the box has been flooded.

Inside the box there could be quantities of rust from corroded steel. This would be conductive and could explain the voltages on low impedance that you measured.

View attachment 196761

I would seriously look at replacing the entire cable as the amount ( length ) of corrosion of the SWA is un-known

As per my post near the beginning.

Water can travel uphill as well as down hill due to capillary action. This is particularly true if the cable is stranded wires.
I'd stop all the faffing and run a new cable in, making sure you keep both ends sealed until you are ready to terminate them.

Read more: https://www.diynot.com/diy/threads/swa-failure.546741/#ixzz6Pzf7Uq7v

 

[defadog]

Replacing cable on this site is a nightmare. Plan is to usecabove ground box fixed to retaing wall
https://www.tlc-direct.co.uk/Products/PRABX23.html
Will test the cables to see if they needcreplacement once the joint is out.

New TT earths at garage and shed to ensure that I am not relying on SWA sheath.

Assuming cables are sound, does that sound sensible?

 

[bernardgreen]

New TT earths at garage and shed to ensure that I am not relying on SWA sheath.

The SWA metallic sheath must be Earthed at the supply end ( CU in the house ) and be continuous for the entire length of the SWA cable.

You should not connect the metallic sheath to the TT Ground rods as a fault in the house supply ( lost Neutral ) could lift the house "Earth" potential above Ground potential. This could result in high currents from the house "Earth" along the SWA metallic sheath and into the TT Ground rods. This would lift the "Earth" in shed and / or garage to a potential significantly and possibly dangerously above Ground potential.

There are no protective devices to limit this "Earth" to Ground current as it flow along only the "Earth" conductors.

 

[defadog]

Bernard, plan was to ensure continuity on the sheath as far as the connection to the garage and shed, but not use it for the earth in those two buildings. So completely seperate TT earthing in both. Alternatively I can leave as is..with house earth exported to both buildings via the sheath?

I will be getting a professional in for the repair...but want to ensure I have all the required parts.

 

[dannyboi2003]

That looks like it took some effort to expose! That does look like a proper Y resin joint compared to the butchered one you found serving the shed. It’s probably failing though and water has found its way inside and stared to corrode the connections or when it was connected together the joint wasn’t tightened well enough and its burnt out. Hopefully cutting that out and replacing it will fix your voltage problem

 

[RF Lighting]

I would install a new underground joint personally.

If properly installed, there is no better joint available. Unfortunately it appears your joints have not been installed very well.

Where abouts are you in the country?

 

[defadog]

Update. Joint was completly shot, and water had got in. But now the mystery. Can someone explain why there has been no problem with supply to garage, yet with the joint removed and cables rejoined to garage only, the mcb now breaks even with the wires open circuit? Currently inside an IP68 box in a terminal block to prevent damage. Tested voltage..fine. but wht would mcb go when open circuit when it didnt go when in the damaged join?

 

[defadog]

RF...in wales. Cannot use an underground joint ...cable only 10cm beneath path. So will put inside proper underground conduit, and use pratley orange box on retaining wall so it is clear it is there. If I can get the cable problem fixed that is.

 

[defadog]

but there is one positive...having discovered the pme earth had been exported, I can at least fix that!

 

[securespark]

If you know someone who has a time-domain reflectometer (TDR) it might pin point if there's another joint or issue?

That sounds like something that belongs in a time–travelling DeLorean....