I discovered this in a property this week, so what is it?
This Green Goo or Greening can look like something out of a horror movie, it is caused by the plasticiser used in the making of the PVC cable insulation reacting with the copper wire and warmth of the house and leaching out. It has the appearance of fairy liquid and in mild cases wont be noticed by the home owner until some electrical work is being carried out, but often it can be very apparent, oozing down light pendant cables to the bulb holders or leaking out of light switches and sockets leaving a green stain down the wall.
This problem is most common in houses built or rewired between 1965 and 1971 and is a due to a fault in the manufacturing process, PVC cables require a plasticiser to make the cable pliable. Modern plasticisers don't usually react in this way.
The Goo can cause functionality problems with light switches and sockets, and in worse cases can cause the insulation of the cables to crack and fail.
The Green stuff is mildly toxic and can cause burning, dermatitis and irritation, particularly when in contact with the eyes, nose or mouth.
So what do you do if you find your property is affected? Sadly the only real treatment for this is to rewire the effected circuits and fuse boards, simply replacing the affected switches etc. will only be a temporary fix as the Green Goo will return.
The Electrical Safety Council advises that all such remedial work is undertaken by a registered electrician.