I have seen what looks like green gunk seeping out of some old twin and earth cables. What is it and what should I do?
Green gunge (also known as green goo) is sometimes seen exuding from the ends of older PVC insulated and sheathed cable. It is normally seen in cables made in the 1960s and 1970s, but not generally seen in modern PVC cables.
Its origin is the plasticiser used to provide flexibility in the PVC polymer compound. This is generally di-octyl phthalate, which over time or with excessive heat has reacted with the copper conductors to produce copper phthalate (hence the green colour) suspended in the liquid plasticiser. The material is a health concern, so should be handled with care – gloves should be used and waste disposed of properly.
Although there does not appear to be a problem with the electrical performance or safety of the cable itself, any exuded gunge should be removed as it can cause corrosion or affect the action of switches and terminations, potentially resulting in tracking / overheating. It can also cause cosmetic problems such as staining. The affected circuits should be rewired as soon as possible.
The original manufacturer of the cable should be contacted if there are any additional questions.