Here is a picture of paint overspray that has contaminated the bus bar in an electrical panel. Paint overspray and other foreign substances should not be present on components inside an electrical panel, especially on the bus bar. This is because the paint can interfere with safe operation of the panel. If a breaker is installed in this open slot pictured, full contact with the bus bar will be impaired because of the paint. This will cause the electrical current to have to jump across a gap rather than smoothly flow. This jumping or "arcing" as it is known creates excessive Heat which can result in melting breakers and possibly an electrical fire. When paint is present inside an electrical panel, a licensed electrician will need to evaluate the panel further to determine what types of repairs or replacements are required.