Advice for wiring in walls with damp

[MikeKing]

Hi all,

Was called to a house with a tripping RCD this week, traced it to the basement socket ring. The house is a ground and basement floors, with the basement excavated and converted into the living room and is about 5 years old, DB is up on ground level.

Very low IR readings across the main section of cabling in the basement and customer tells me that he has had a huge problem with damp coming in through the basement walls, existing cabling is unprotected t&e into cavity boxes. I know the obvious answer is to get the damp fixed. I'm sure he's on it, but in the mean time, he needs to get the situation remedied. The circuit needs rewiring but I wanted to ask for some collective advice on a wiring method that would offer a long term solution should the problem reoccur.

Surface cabling and sockets is definitely not a preferred option.

I was thinking a couple of options,
Rewire faulty section (almost whole thing) in armoured, although that would mean galv back boxes which will just rust over time.

Research on forums has suggested, pvc conduit into surface boxes, but recess them and silicone joints.

Just wondering if there was an obvious trick I was missing??

Thanks in advance.

 

[Wilko]

My thought is to double check that damp was the cause. To trip an RCD it needs say 16K ohm or less, which is pretty low for a bit of damp, just saying.

 

[littlespark]

The damp would only affect the cables at the terminations, so changing the cable to armoured wouldn’t have much effect.

T&E sheath is quite waterproof until it has a nick in it.

Were the cables disconnected to give low IR readings or are you picking up connected equipment

 

[buzzlightyear]

Is you customer called rigsby reasirig damp , if the back boxes are sealed then no more damp , but if the basement has been tanked then he sould not have problum.
[automerge]1576570513[/automerge]

 

[davesparks]

The only real solution to this is to cure the damp problem.

The dampness is unlikely to be affecting the cables so I doubt it needs to be rewired.it is almost certainly just affecting the terminations where condensation forms a layer of moisture between terminals.

Heat and dehumifiers in the room may help with this. Other wise high IP rated accessories would be an ugly but effective measure.

 

[phil 01]

The only real solution to this is to cure the damp problem.

The dampness is unlikely to be affecting the cables so I doubt it needs to be rewired.it is almost certainly just affecting the terminations where condensation forms a layer of moisture between terminals.

Heat and dehumifiers in the room may help with this. Other wise high IP rated accessories would be an ugly but effective measure.

Most people don’t understand how tanking a room works, basically your making a sealed box within the room with drains around the room to a collection point and the water is pumped out, possibly a small sump pump, the membrane that fitted around the room completely seals it from the incoming water, you can’t stop the water coming in you just manage it. So now installing our electrical system become difficult, penetration of the membrane shouldn’t be carried out without a specialist with you to reseal the area, but probably shouldn’t be done at all.

 

[static zap]

Would you TT an install like this for safety ?
--or is everthing in the lounge double insulated--
(it's a bit like being outdoors)

 

[MikeKing]

Thanks for all the replies, the IR testing was done with the legs disconnected.

It was my impression that the T&E would have been ok in damp, not ideal but ok, I agree it would have likely to only have been effected at the terminations. Although one of my guys said he actually got a little tingle on the T&E through the grey outer sheath on a L-->E IR test.

I like the idea of tanking. Although sadly this is beyond my scope of works, although I will mention it.

 

[Strima]

I had similar in a pub last week, building around 300 years old and rewired 5 years ago. The walls have had a layer of waterproof membrane place between internal and external but the brainiac who fitted the sockets decided to cut out the plastic to fit the back boxes.

Move forward five years the cables are now mouldy and the screws had rotted out to the point where the socket would pull out.

This was on an EICR so I wouldn't normally repair but with public access I needed to sort it just in case.

 

[westward10]

The damp would only affect the cables at the terminations, so changing the cable to armoured wouldn’t have much effect.

T&E sheath is quite waterproof until it has a nick in it.

Were the cables disconnected to give low IR readings or are you picking up connected equipment

PVC sheathed cables are not waterproof at all they are merely resistant to water. Prolonged immersion in water will eventually penetrate the PVC sheath. Water is a persistent solvent and will pass through the PVC.