Best way to deal with moisture in cable

[bhavik]

I have a 6mm cooker cable in the wall. Perhaps a choc bar connector has been used (don't know for sure). The cable is showing continuity after disconnecting each end and testing. This suggests moisture perhaps. (Lots of cats around so no mice or rats. )

Is it worth trying to clear the moisture by passing high voltage to heat the cable?
Any suggestions on equipment e.g. Robin

(Client had a similar problem 15 years ago when new kitchen was installed but don't know what was done.)

 

[DefyG]

Or damaged cable but either way the fault or joint needs locating and eliminating to be 100% sure! Re-wire?

 

[bhavik]

Or damaged cable but either way the fault or joint needs locating and eliminating to be 100% sure! Re-wire?

I am afraid part of the cable is in the wall and part above suspended ceiling (which could be broken). Mostly not easily accessible. A new cable could be run. Might be easier to attempt to remove moisture if it lasts another 15years!

 

[James]

The fault needs to be physically found and repaired.
alternative is to replace the suspect piece of cable with new.

trying to warm it by passing current down it is just not an option as you have no way of determining what damage has been done to any junctions or insulation brake down along the cable.

 

[bhavik]

The fault needs to be physically found and repaired.
alternative is to replace the suspect piece of cable with new.

trying to warm it by passing current down it is just not an option as you have no way of determining what damage has been done to any junctions or insulation brake down along the cable.

I have a fair idea that the issue is likely due to moisture. Sometimes vermin can chew and damage the cable but this is not likely in this case. Cable is only about 15 years old. The installer may have taken a short cut by using choc bar connector to lengthen the cable and this is probably where there may be moisture. Best fix is probably to run a new cable. But if moisture can be removed and the problem does not recur for a long time, it might be a more aesthetic and economical solution.

 

[telectrix]

 

[James]

How can you ensure that the cable or joint has not been damaged by the moisture?
sounds like a fire ready to happen.

 

[Moley]

Sounds like a fire ready to happen.

Well, that would cure the moisture.

 

[bhavik]

How can you ensure that the cable or joint has not been damaged by the moisture?
sounds like a fire ready to happen.

It's a valid point. Based on age of cable and nature of issue I am assuming that the damage is not severe. The RCD would continue to trip if damage is severe after attempting to remove moisture.

 

[James]

Sorry to say this, but no matter how many ways you try to justify this “fix”

it is a DODGY DIY FIX, no professional in there right mind would do this and HOPE the problem goes away for a few years.

 

[westward10]

What value of continuity are you getting and between which conductors.

 

[bhavik]

Sorry to say this, but no matter how many ways you try to justify this “fix”

it is a DODGY DIY FIX, no professional in there right mind would do this and HOPE the problem goes away for a few years.

Agreed. The best solution is new cable. But client may prefer to do that later when replacing the kitchen etc

 

[bhavik]

What value of continuity are you getting and between which conductors.

I am afraid my fluke 1652C went dead. Hoping to get replacement soon. I did check continuity but can't remember the values. Will get back after checking again.

 

[James]

You are listed as a trainee electrician, what does your tutor / mentor / electrician you are working with say about this?

clients often have little understanding about the dangers involved with electricity, it makes no difference and doesn’t surprise me that the client would like it fixed cheep on the promise that it may get redone in the future when other work is done.
however, as an electrician we should only ever give options to them that are safe And can be certified as compliant.

 

[JBW175]

What conductors were you getting continuity between?

Did you IR test the circuit?

What were the original symptoms that led to you being asked to conduct investigations?

 

[westward10]

We're you doing continuity or insulation resistance.

 

[UNG]

So 15 years ago the kitchen fitters bodged the electrics and left a fault waiting to happen, now the OP now wants to bodge the electrics again to avoid the reality that the only real fix may mean taking some plaster off

You are listed as a trainee electrician, what does your tutor / mentor / electrician you are working with say about this?

His profile also has " Business Name Bhavik Shah IFA " wondering if that is why he is trying to fix it on the cheap

 

[bhavik]

What conductors were you getting continuity between?

Did you IR test the circuit?

What were the original symptoms that led to you being asked to conduct investigations?

Original symptoms were RCD tripping. Haven't done a lot of testing yet. Continuity between live and neutral.

 

[westward10]

Original symptoms were RCD tripping. Haven't done a lot of testing yet. Continuity between live and neutral.

Continuity or insulation resistance.

 

[bhavik]

So 15 years ago the kitchen fitters bodged the electrics and left a fault waiting to happen, now the OP now wants to bodge the electrics again to avoid the reality that the only real fix may mean taking some plaster off


His profile also has " Business Name Bhavik Shah IFA " wondering if that is why he is trying to fix it on the cheap

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

 

[bhavik]

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

 

[bhavik]

We're you doing continuity or insulation resistance.

Only tested for continuity so far.

 

[UNG]

If there is moisture in the cable are you sure you don't need a plumber or a roofer

 

[Moley]

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?

 

[bhavik]

If there is moisture in the cable are you sure you don't need a plumber or a roofer

depends on where the cable is.

 

[James]

True. It could be somewhere really wet!

 

[bhavik]

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.

 

[UNG]

Your assumption is it is a moisture issue but it could also be a melted or failing connector block or even rodent damage

 

[JBW175]

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.

 

[bhavik]

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).

 

[bhavik]

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.

 

[JBW175]

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.

 

[westward10]

I doubt moisture would introduce a low enough resistance to show physical continuity.

 

[littlespark]

Neon on the cooker switch?

Random thoughts, haven’t read the rest of the replies..

 

[James]

Neon on the cooker switch?

Random thoughts, haven’t read the rest of the replies..

Op said cable disconnected both ends.

 

[bhavik]

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.

 

[Lucien Nunes]

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.

 

[bhavik]

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.

 

[bhavik]

IR testing:
Live to Earth is only 0.01 mega ohms (10 KΩ) when testing at both 250V and 500V.

Live to Neutral and Neutral to Earth are both 200 mega ohms (250V), 500 mega ohms (500V).

 

[ipf]

Suggest you find the choc bar connector to see if it's melted.

 

[JBW175]

IR testing:
Live to Earth is only 0.01 mega ohms (10 KΩ) when testing at both 250V and 500V.

Live to Neutral and Neutral to Earth are both 200 mega ohms (250V), 500 mega ohms (500V).

Looks like it’s time to start lifting up floors and digging into walls to find the problem then.

At least you know what part of the circuit it’s on after splitting it down and IR testing it.

 

[bhavik]

Suggest you find the choc bar connector to see if it's melted.

Would like to do that. But may not be practical as part of the cable is in the wall. If the connector was found (for example in a suspended ceiling), what next?

 

[James]

Would like to do that. But may not be practical as part of the cable is in the wall. If the connector was found (for example in a suspended ceiling), what next?

Take a photo of it and post it in dodgy trade pics thread.

then cut back the cable to the undamaged part and using correctly rated maintenance free connections repair it.
test
certify
give happy customer the invoice

goto local pub for a pint or local cafe for cheesecake

 

[littlespark]

goto local pub for a pint or local cafe for cheesecake

Save time and find a pub that serves cheesecake. Or a cafe that sells beer…..

Or cheesecake flavoured beer.

I’m calling it!

 

[UNG]

Would like to do that. But may not be practical as part of the cable is in the wall. If the connector was found (for example in a suspended ceiling), what next?

You need a cable tracer, should lead you to where the fault is

 

[bhavik]

Take a photo of it and post it in dodgy trade pics thread.

then cut back the cable to the undamaged part and using correctly rated maintenance free connections repair it.
test
certify
give happy customer the invoice

goto local pub for a pint or local cafe for cheesecake

https://community.NoLinkingToThis/threads/extending-the-existing-6mm-cooker-cable.52161/

Yellow in line connectors:

4.0mm² - 6mm² Yellow In-line Butt Connectors

www.tlc-direct.co.uk

 

[Lucien Nunes]

I don't trust no-brand insulated crimps on 32A circuits. Plus, you'll need to join the 2.5mm² solid CPC and most crimps are not suitable for solid cores (some are, but they are specific types and you must use the matching tooling which can be £££)

Would suggest three Wago 773-173's which do 2.5 to 6.0. and are rated for 41A:

Wago 773-173 Push Wire Connector 2.5mm - 6.0mm 3 Way | Wago_Connectors (773-173)

www.tlc-direct.co.uk

 

[bhavik]

Continuity readings:
L E. 0.15 ohms
N E 0.88 ohms

 

[bhavik]

You need a cable tracer, should lead you to where the fault is

Any recommendations on cable tracer?
Most will trace the wire. I presume the signal would weaken around the fault. There are loads on market from cheap to the expensive fluke 2042

 

[Lucien Nunes]

Continuity readings:
L E. 0.15 ohms
N E 0.88 ohms

Really ohms?

This thread started off all about moisture but now we get onto the actual readings they are perhaps 10,000 times lower than moisture is likely to be responsible for. Unless it's raining mercury?

That's a proper short-circuit you have there, a nail through the cable or similar, and all three conductors involved too.