Corrosion of metal parts and pieces is generally bad...unless your nick-name is "Rusty". When these metal pieces are components of an electrical system...It's time to get "Hot After It"!
In the magical world of electrical systems...corrosion equals resistance, and resistance equals heat generation by arcing and sparking. Corrosion can occur at electrical terminals, such as found in main service panels at the breaker lugs, or at receptacle (outlet) locations where the wiring is connected the fixture. Corrosion can result from the improper tightening of the lugs or screws fastening the conductive wire system to the fixture or breaker. If the lug is not tightening properly, then the arcing and sparking of the current across the gap (no matter how small) will generate heat and cause the loss of electrons from the surface of the metal parts. This loss of electrons from the metal surface is "corrosion" and causes a "crusty" surface to appear. The corrosion also causes a resistance to the proper flow of electricity through the electrical system, which causes increasing arcing, sparking, heat production and more corrosion. If the environment in which the electrical system is in has a high humidity level, like those found in vacant houses or with wet / damp basements, then the rate of corrosion is increased.
To reduce the risk of corrosion occurring along the electrical components, a qualified licensed electrician will properly tighten all connections and may also use an electrically conductive / anti-corrosion paste or jell at the connections. When corrosion is observed with existing copper wire systems, then contacting an electrician is an important first step in correcting or replacing the damaged parts. If corrosion is observed with existing aluminum wire systems, then the recommendation to contact an electrician is even more urgent!! Aluminum wire, when acted upon by corrosion and the increased heating of the wire in this location, will expand in dimension when heated, causing extreme pressure on the connection and then return to its normal dimension when the current is off. When the current is re-energized, the connection gap is likely to be somewhat larger, causing a larger arc or spark and more heat generated!!
Having a professional home inspector evaluate an electrical system for its current condition is recommended for protecting life, health and property. A little corrosion can go a long way to causing big problems!!