This may be an old topic for seasoned home inspectors, however I feel it is worth taking another look at this issue. I first noticed this several years ago, and am not to proud to admit that I thought it was dielectric grease. After further research I discovered that this is actually the breakdown of a “plasticizer” used for the wire insulation. They added this to make the wire more flexible. Elevated temperature and possibly humidity can cause the plasticizer compound to separate from the insulation on the wire. The plasticizer can then travel along the wire and be visible on the exposed part of the wire or on a device like a circuit breaker or receptacle. Common wire insulation has an outer nylon jacket. The plasticizer cannot penetrate this jacket, therefore it runs down the wire strands or conductors. This is why it is most noticeable where the wire conductors are exposed or at a termination. The effects of this process cause the wires to become less flexible and more brittle. Residue on devices may also cause connection issues and possibly failure. What should a home inspector be looking for and how to advise your client:

• Green oily residue – this should not be confused with dielectric corrosion
• The surfaces should not be cleaned
• This may be confused with lubricant use to pull wires.
• The oily residue is normally found on the ends of the wires or where the conductors are connected to a device, NOT on the outside where a lubricant may have been applied in order to pull wires through conduit
• If this residue is observed, the electrical equipment and devices are probably damaged. The residue may have entered the inside of the components
• The “plasticizer” is a petroleum based product and may cause deterioration to insulation used in some electrical devices
• Recommend your client seek the services of a qualified electrician to evaluate and replace any areas where this has taken place

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