Technical Article - Green Gunge or Green Goo
Green exudate from PVC
PVC
PVC comes in two main grades, plasticised and unplasticised.
Unplasticised PVC (UPVC) is used for example in double glazing window frames where a rigid material is required.
The PVC used for manufacture of cables is a plasticised PVC that conforms to the relevant British Standard for the cable type in question.
Ageing effects
As a cable ages (at temperatures above normal ambient) the elongation to break decreases (also the Insulation Resistance increases). The life expectancy of a cable is arbitrarily considered to be when the elongation to break of the PVC is 50%.
A lower elongation to break value could be considered suitable especially for a fixed wiring cable. Therefore, providing the cable is not subject to movement or when moved due to inspection of socket outlet or the like, the PVC does not crack, a much lower value of elongation to break is considered by some as suitable.
Greening
Greening is the appearance of a wet green substance that is a product of an adverse reaction between certain types of plasticiser and the copper conductors. This greening, which is a rare occurrence, can happen either after a long period of time for some cables, or if the cable has been severely overheated
The Approved Cables Initiative (ACI) on CPR:
Construction Products Regulation (CPR) ensures consistent information is available for those who need to know by enabling the performance of construction products throughout the EU to be assessed and compared irrespective of the manufacturer or country of origin.
The Approved Cables Initiative recently launched a campaign to highlight the 'CPR' requirements - the results are expressed in a hierarchical series of classes (Aca down to Fca). Please watch the video and access our CPR page.