As a homeowner, you may come across cables, switches or sockets that  ooze a sticky green goo that has a strong odour. Here’s what causes it, and what you can do about it…

The green goo that you see is the product of a reaction between decomposing plasticiser (a plasticiser is an oily liquid used in the manufacture of PVC compounds) and the copper conductors of PVC cables. It’s better known as cable ‘greening’.

The decomposition of the plasticiser is caused by overheating the PVC compound. It is usually a slow process, but can be accelerated when high temperatures are involved. High temperatures can be caused by external reasons, but overloading and loose connections are two common examples.

Although all cable grades of PVC may look the same, the cheaper grades can be more prone to producing the green goo. The main instances of ‘greening’ cable arose during the 1960’s and 1970’s, although some instances are still seen today. Inferior grades of plasticiser were prone to greening even if the cables were not overheated.

The plasticiser of better grades of cable, such as those produced by Prysmian contain an antioxidant which inhibits the decomposition rate of the plasticiser when heated. Even these plasticisers can be broken down eventually under adverse conditions of heat, but are much better protected than those which do not contain an antioxidant.

Although fumes may be given off when PVC is decomposing (this statement is applied to house wiring) it would not be considered to be a health hazard, but there is a danger that the breakdown of a cable could cause an electrical fire.

The plasticiser itself is a clear oily liquid that is non-conductive. The green substance is a combination of copper oxide and plasticiser which is conductive. Therefore, whenever this green substance is found at socket outlets etc. it should be removed and the terminations cleaned (gloves should be worn) otherwise it is possible that tracking/overheating may occur. It is normally considered that if greening is found that rewiring should strongly be considered.

In terms of solutions, the options are limited, but two to consider:

1. A full or partial re-wire – though this may not be desirable unless the property is empty and you have the budget!

2. We have come up with a special way to deal with this at each socket or switch location that causes minimal damage to the wall.
Please contact us if you’d like to resolve this issue in your home.