Electrical insulation embrittlement

The consequences of oxydative and thermal breakdown of a polymer are discolouration, surface roughening, embrittlement, etc. for rubbers tackiness, followed by embrittlement. For electrical applications oxidation goes accompanied by a strong increase in the dielectric losses, and a decrease in insulation resistance and breakdown strength. 

Polycarbonates insulating and other electrical properties are excellent and remain almost unchanged by temperature and humidity conditions. One exception is arc resistance, which in PCs is lower than in many other plastics. They are generally unaffected by greases, oils, and acids. Water at RT has no effect on PCs, but continuous exposure in 65 C (150°F) water causes gradual embrittlement. They are soluble in chlorinated hydrocarbons and attacked by most aromatic solvents, esters, and ketones, which cause... 

Mineral-insulated, metal-sheathed (MIMS) cable is suitable for use in most environments, but it is not so suitable for use where there may be vibration. In an old paint spray booth which predated the Highly Flammable Liquids and Liquefied Petroleum Gases Regulations, a spider-frame-mounted, electrical extractor fan had been positioned at the mouth of the extract duct and connected by MIMS cable. The fan motor was totally enclosed and explosion-protected as the paints used were flammable. The maintenance was poor and paint accumulations were allowed to build up on the fan blades causing an imbalance and vibration. This led to embrittlement of the copper sheath of the cable, which cracked and broke. Then one of the conductors fractured and sparking occurred between the ends. Ignition of the spray started a fire in the paint accumulations on nearby surfaces and the factory was burnt down. 

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