water in an outdoor JB and effect on SWA glanded in on the lower edge

The cables may dry out to some extent but the life will not be greatly changed although the armour may suffer a very small amount of corrosion. Armour corrosion requires that the water is changed frequently as once it reacts with water the water is unreactive, and Hydrogen is given off.

If possible a hair drier can be used to drive any moisture out from the cable to an open end. It will take time though. The heat will not be enough to damage the cable. The process is similar to using a blowlamp on damp M.I.C.C. cable to drive out moisture to an open unterminated end. Start by warming the cable about a metre from the end and work slowly towards an open end. This may take several passes with the hair drier.

Z.

We hope it's not this bad.

I had to replace a metal distribution board a few years ago. It was connected by SWA to a junction box 5m away and 1m higher. Water had got into the junction box, run through the SWA and into the distribution board in sufficient quantity to turn it to rust. Once dried out the SWA tested OK, but maybe it's life was shortened.

I may have posted this before but during an inspection the installer took off the lid of a 3-ph DB to see a puddle of water in the bottom plate where the incoming SWA was glanded off. He immediately thought of it being a leak from the roof above but I suspected SWA cable damage where buried from the elevated supply source. On drying out the gland plate you could actually see the water rising through the gland. Somewhere upstream (sorry, couldn't resist it!) the SWA had been damaged (not buried in sand or a duct) and water was getting into the sheath and capillary took over.

As to corrosion, the SWA wires are only zinc plated and will rust and eventually break. I stripped an old SWA to see how far water had gone and it was far beyond the concept of hairdryer use as I gave up after 25 m.

Regards

BOD

The only cable types that survive this unaffected are the ones that have wax or petroleum jelly  pressure filled into the voids between the cores at manufacture - and that is not normal SWA in the UK . If not you should assume it will have got wet pretty much all the way along, and will remain wet more or less for ever, whatever you do with tissues or gentle heating, unless it is very recent ingress.

So run the normal tests, with attention to insulation and armour continuity in particular, and mark up a relatively short duration to next inspection - if the water has been running down inside the cable for a few years it may well be pretty much ‘lifed’. If the water coming out is brown, the armour wire galvanising has been removed and it is eating into the steel already.

The current rating may be slightly enhanced, thought you will know if it boils.

Mike.

thank you all for the comments

of course it is best nothing like this scenario happens, but if it does it would  seem (in relation to implications from comments) that DaveZ comments would be the ‘best’ outcome, but in reality it is likely somewhere in between that and total bust - hopefully not too bad though.