Verdigris is a bright greenish-blue hue patina of copper carbonate or likely Di-n-Octyl Phthalate formed on copper or brass by atmospheric oxidation affecting electrical cabling. Its a a plasticiser leaking from older PVC insulation.

It is a poor conductor of electricity. It increases electrical resistance, inefficient current flow & overheating. Verdigris indicates corrosion, weakening structural integrity of cables & cable failure.

Chemical reactions producing Verdigris degrade insulation material & short circuits or electrical fire or equipment malfunction.

Causes
PVC in your electrical cable degrades and reacts with the copper wiring. This occurs due poor manufacturing practice which resulted in a sub standard plasticiser being used. The plasticiser leaches from the insulation when warm, and then reacts with copper and producing a tacky green substance.

• Overheating: High temperatures from overloading or loose connections can speed up the decomposition process 
• Age: Older cables are more likely to experience cable greening 
• Grade: Cheaper grades of PVC cable are more likely to produce green goo 

Effects

• De-plasticisation: The process of cable greening de-plastifies the insulation, which can eventually cause the PVC to  become brittle and crack 
• Tracking and overheating: The green substance is conductive, so it can cause tracking and overheating if left at socket outlets.  
• Corrosion: Greening or Verdigris corrodes copper cables and connections

• Health hazard: While seemingly harmless, it can pose health risks. Touching or ingesting the substance can be hazardous, especially for young children 

Solutions

• It is strongly recommended that the affected area be rewired when cable greening is discovered.
• Clean the substance with a rag soaked in a petroleum- or alcohol-based solvent 
• Remove the substance and clean the terminations 
• Seal all areas to minimise air circulation to minimise oxidation effects