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Intention is to replace cable eventually.

Client history suggests similar problem occurred when the new kitchen and wiring was done 15 years ago.
I was wondering of others experience and long periods of remission after treating moisture.
Some electrical safety certificate was issued after the works were completed 15 years ago
That should be somehow
 
If there is moisture in the cable are you sure you don't need a plumber or a roofer
 
If theres enough water in the cable to show up on a continuity test then that cable is scrap. If it was an IR test I could understand it but continuity? Are you sure it's water and not the insulation damaged somewhere?
 
True. It could be somewhere really wet!
Best way to deal with moisture in cable 1657102575827 - EletriciansForums.net
 
In conclusion answer generally seems to be: 'Do not remove moisture, replace cable.'
Thanks to all those who replied and shared your knowledge and vast experience.

I think that myself and the other members have concluded that you need to carry out some more comprehensive testing and stop being so vague in your answers.
 
Thats true. Assuming it is moisture and it is removed for example by passing current at high voltage on a resistance setting, I wonder if an electrical safety certificate would be issued (this is sort of what happened 15 years ago).
 
I think that myself and the other members have concluded that you need to carry out some more comprehensive testing and stop being so vague in your answers.
Apologies, I should have posted after more thorough testing. Unfortunately, my tester (fluke 1652C) died and I hope to get a replacement soon.
 
Apologies, I should have posted after more thorough testing. Unfortunately, my tester (fluke 1652C) died and I hope to get a replacement soon.

And I apologise for maybe coming across as being a bit harsh, but it’s a cooker circuit and in an ideal world, It should run from CU to isolator, then from isolator to cooker connection plate.

The very least you need to do is split it down at these points and then IR the cable. This will give you a good indication of which leg the fault is on.

Also, with regards to it being a cooker circuit, have you pulled the cooker out and checked the condition of the connection plate?

It could well be that after 15 years of water, soup, and other detritus falling down the back of the cooker, it’s got inside the plate and the fault lies there.
 
And I apologise for maybe coming across as being a bit harsh, but it’s a cooker circuit and in an ideal world, It should run from CU to isolator, then from isolator to cooker connection plate.

The very least you need to do is split it down at these points and then IR the cable. This will give you a good indication of which leg the fault is on.

Also, with regards to it being a cooker circuit, have you pulled the cooker out and checked the condition of the connection plate?

It could well be that after 15 years of water, soup, and other detritus falling down the back of the cooker, it’s got inside the plate and the fault lies there.
Off at cooker switch. from cooker switch goes into isolator. Isolator connects to oven and microwave - no cooker. problem on cable coming in to cooker switch. cable going out from cooker switch to isolator and onwards to oven and microwave is ok.
 
Original symptoms were RCD tripping. Haven't done a lot of testing yet. Continuity between live and neutral.

Continuity L-N won't trip the RCD. It will make a loud bang, spit out some molten metal, leave a burn mark and trip the MCB.

Anyway, let's suppose there's 'moisture' causing leakage L-E. We need to be clear what that 'moisture' is. A bit of condensation on the surface of a terminal block will not trip an RCD, it needs to be properly wet. What is the highest insulation resistance that can possibly trip an RCD? A typical RCD trips around 22mA, let's suppose there's 4mA of leakage already on it and it only needs 18mA from the insulation breakdown. That would put the insulation at 230 / 0.018 = 12.8kΩ. Considering that most circuits achieve 10,000 times better insulation or more, gives an idea of why that's spectacularly low.

0.018 * 230 = 4W of heat dissipated at the fault. That is enough heat to melt insulation and cause rapid corrosion. Then there is the subject of surface tracking. When significant leakage takes place through water over a period of time, metal ions are dissolved from the conductors and can be deposited on the surface of the insulation. This is very much more serious on DC but it does still occur on AC. When the moisture evaporates, a surface track of degraded insulation strength is left behind. If the problem is at terminals they are likely to be badly corroded and high-resistance. The last 'damp' fitting I saw that had just occasionally started tripping an RCD was a double-socket with free water in the back box that ran down the wall when I drew a Stanley knife round it to break the paint seal. It was so badly corroded that the terminal screw heads had rusted away and the conductors were jet black with copper oxide for 3cm inside the insulation.

It's often OK to dry out moisture if it's fresh and / or the parts have not yet been subjected to mains voltage. But it is not safe simply to dry things out when they have likely been simultaneously subjected to moisture and voltage for an unknown period.
 
Continuity L-N won't trip the RCD. It will make a loud bang, spit out some molten metal, leave a burn mark and trip the MCB.

Anyway, let's suppose there's 'moisture' causing leakage L-E. We need to be clear what that 'moisture' is. A bit of condensation on the surface of a terminal block will not trip an RCD, it needs to be properly wet. What is the highest insulation resistance that can possibly trip an RCD? A typical RCD trips around 22mA, let's suppose there's 4mA of leakage already on it and it only needs 18mA from the insulation breakdown. That would put the insulation at 230 / 0.018 = 12.8kΩ. Considering that most circuits achieve 10,000 times better insulation or more, gives an idea of why that's spectacularly low.

0.018 * 230 = 4W of heat dissipated at the fault. That is enough heat to melt insulation and cause rapid corrosion. Then there is the subject of surface tracking. When significant leakage takes place through water over a period of time, metal ions are dissolved from the conductors and can be deposited on the surface of the insulation. This is very much more serious on DC but it does still occur on AC. When the moisture evaporates, a surface track of degraded insulation strength is left behind. If the problem is at terminals they are likely to be badly corroded and high-resistance. The last 'damp' fitting I saw that had just occasionally started tripping an RCD was a double-socket with free water in the back box that ran down the wall when I drew a Stanley knife round it to break the paint seal. It was so badly corroded that the terminal screw heads had rusted away and the conductors were jet black with copper oxide for 3cm inside the insulation.

It's often OK to dry out moisture if it's fresh and / or the parts have not yet been subjected to mains voltage. But it is not safe simply to dry things out when they have likely been simultaneously subjected to moisture and voltage for an unknown period.
Well explained. Good basic maths. Will do more testing in a few days. From the sounds of it, the cable will likely need replacing.
 

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