Cleaning corroded conductors

vwes59 · Apr 2, 2021

Hi,
I've just completed some fault finding on a ring final, as I couldn't get continuity on the CPC, and I found most of the metal back boxes and CPC conductors were in a pretty bad state with lots of corrosion. I did a bit of cleaning up to get bare copper, and it worked enough to get continuity, but the values were still quite bad. Has anyone tried the vinegar/salt and then baking soda method to clean copper to recover corroded conductors and metal back boxes ? It's only the lugs on the back boxes and the first 10mm or so on the conductors, but I don't want to cut them back as there won't be enough conductor left to fix the fronts on.

telectrix · Apr 2, 2021

wire wool for the conductors. replace any bad boxes.

Julie. · Apr 2, 2021

Why is it all corroded?

If its a load of water etc then cleaning would be OK.

However if its the green goo - this could be a bigger problem, this could extend up the core all the way. This was caused by a poor choice of plasticiser for the pvc used in the 1960's which desolved the conductors themselves.

This can cause the cross section to be significantly reduced, this isn't a case of cleaning, as the cable is completely destroyed.

Cable from the mid-late '70s should be ok as the issue was resolved.

Remember the goo is toxic and conductive, another issue therefore is at the bottom of vertical runs it spreads out and can cause short circuits.

pc1966 · Apr 2, 2021

I would be very weary of using any sort of corrosive mix to try and out-corrode existing damage. Most likely it will persist somewhere after you think it is finished and cause more problems for later.

Realistically if it is beyond a bit of a scrub with a small wire brush or wire-wool, then you really should be looking at replacement.

Dustydazzler · Apr 3, 2021

Couple squirts of white vinegar solution and scrub with a wire scouring pad To clean old cables. If the back box is all rusted up it could be damp wall so the damp will need sorting then replace the back box.

vwes59 · Apr 9, 2021

The back boxes were all dry, so I'm not suspecting a water leak. Cables were all renewed in roughly 2012 (That's the date on the consumer unit). My suspicion is that the fronts were put back on before the plaster dried (There were plaster splashes on the back of the front plates), thus it was "damp" behind the fronts. I've looked into it a bit more, and it's common for the CPC to be affected by corrosion and not the other conductors if damp, condensation etc is involved, and I believe old lime based plaster can react with the zinc in the back boxes and the copper in the conductors if any amount of water is introduced.

I've seen one solution to this is to use plastic back boxes where lime plaster is suspected to form a barrier between the plasterwork and the cables.

Anyway I'm due back on Monday, so I'll clean it all up, replace any fly leads and fronts that are beyond repair and see what readings I get for continuity and IR and take it from there.

btw there is a video up on youtube on this, so comments welcome.

telectrix · Apr 9, 2021

vwes59 said:
The back boxes were all dry, so I'm not suspecting a water leak. Cables were all renewed in roughly 2012 (That's the date on the consumer unit). My suspicion is that the fronts were put back on before the plaster dried (There were plaster splashes on the back of the front plates), thus it was "damp" behind the fronts. I've looked into it a bit more, and it's common for the CPC to be affected by corrosion and not the other conductors if damp, condensation etc is involved, and I believe old lime based plaster can react with the zinc in the back boxes and the copper in the conductors if any amount of water is introduced.

I've seen one solution to this is to use plastic back boxes where lime plaster is suspected to form a barrier between the plasterwork and the cables.

Anyway I'm due back on Monday, so I'll clean it all up, replace any fly leads and fronts that are beyond repair and see what readings I get for continuity and IR and take it from there.

btw there is a video up on youtube on this, so comments welcome.

post a link to the video.