blue liquid in light switch Ask questions and find answers to many subjects relating to electrics and electrical work

[Phil Russell]

A light switch was crackling so I removed it to replace it. There was a quantity of blue sticky liquid on the wires, some had run down onto the switch N (out) terminal and effectively gummed the wire retaining screw. Wire insulation looked Ok in the pattress but the liquid is obviously coming from somewhere. It appears to be within the grey cable insulation, not within either the N or L wires. The supply cable is twin and earth .. the earth is bare copper and, as the liquid is blue, I suspect it is copper based.
What does this mean? I guess I should get the house wiring checked ... is the blue liquid a sign of imminent cable failure?

All help would be appreciated.

Cheers, Phil

[kbrownie]

Hi Phil Russell,
where is this cable situated, sounds strange is there any chance of water ingress in to the cable from another source ie. plumbing above or ceiling/roof.
Regards
KB

[333rocky333]

seen similar a few times but it has been green, usually in older council houses ,where the wires are in steel pipe down to switches ,sometimes more than one switch is like it .
although grey still used ,most grey was previously stranded possibly over 20 years old ,as it then became common to use the solid white cable.
I was told it is where the cable sweats, sometimes due to heat of a bad switch connection and the conductors which were copper with a silver type of coating, react with the pvc type sleeving they used to use then,apart from renewing the wires theres not much you can do
When you remove this and strip it ,it is throughout the cable for about a foot
It may be wise to get the circuit insulation resistance tested ,to check the cable is not breaking down .
It could also be that current is flowing via the bare earth wire if you have one ,due to earth leakage,causing the cable to overheat.
If there is no earth in the cable then you are overdue a rewire
unless you have double pole switches you are unlikely to have a neutral there.
If you have any metal switches I would make sure there earthed ,for your safety,until you get it looked at.

[kuzz]

The green goo! this is ectoplasm left by ghosts and nothing to do with cable manufactured between 1965-71 having a plasticiser in the insulation that reacts with the copper. The ectoplasm is green (or blue in some lights) due to copper oxide.
you do not have a plumbing problem.
The silver coating rocky referred to is tin. Tin coated copper is from around the same era & was used a lot when Britain was struggling to get copper from the copper mines of zimbabwe, but this cable is not prone to ghosts leaving there slimy deposits.
Anyway the answer to your problem is to get an expert to carry out a periodic inspection, then take it from there.

[333rocky333]

[quote="kuzz"]The green goo!
Dear kuzz
for future ref was there two types, tinned and untinned made then, and you say only the untinned had this problem, if so was this made for both earthed and unearthed versions of the cable and did they tin the earth as well as the cores, if it is a reaction would it be through the whole length then,and could temperature enhance this process, but only become evident where the cable is vertical and eventually runs out.
I am interested as this info dates the wiring and whatever type seems as you say over twenty years and well due for testing
I have come across this few times now
Thanks

[Phil Russell]

Thanks for the suggestions. To answer some questions: the house was built in mid 60's. Lighting able is 3 strand black sheath, 3 strand red sheath, solid bare earth. Switch is clearly single pole with red connector in and black out. location is downstairs toilet with vertical water pipes not too far away on the outside of the wall. It has been suggested that the problem is one of condensation. The insulation looks OK but we will get the circuits checked. Certainly cleaning the wires and replacing the switch has cured the 'fizz'.
Cheers, Phil