There are times when a DC motor or generator experiences a catastrophic failure and the customer wants to know why it happened. One type of failure that seems to stimulate lively conversation is when the failure involves dramatic damage to the brushholders and commutator. The term "flashover" describes the appearance of the failure; the very name conveys an accurate mental image of the failure. The questions that arise next are predictable: "What caused this?" and "What can be done to prevent a recurrence?" Or, if the motor was recently repaired: "What did you do to my motor to cause this?!" The purpose of this article is to help you answer those questions.