Burning bars happen primarily from commutator contamination. Contamination is caused by chemicals, dust, and brush wear. Preventative maintenance is key to finding and stopping burning bars before they cause major problems. Changing brushes that are worn can stop burning bars, as can periodically inspecting in the condition of winding insulation. Certain factors may be present as well that indicate burning on slot bars along with unusual markings. This includes incorrect neutral setting, improper interpole strength, contamination, and electrical overload. If the trailing edges on the dark bars are burned or etched, the commutator should be resurfaced.