Can a shaft brush be safely applied on a motor in a Class I hazardous location?

摘要

Some inverter-fed motors, especially at higher power ratings, are supplied with a shaft brush in order to help mitigate bearing currents. As more inverters are applied to motors in Class I, Division 1 / Zone 1 and Division 2 / Zone 2 locations, there is a need to understand whether a shaft brush can be safely applied in such an environment. This paper addresses the physics of why this is a concern and a methodology to evaluate the relative safety of two example cases. These issues are considered from the perspective of users, manufacturers of inverters and motors, and certifying bodies. The question posed in the title of this paper is answered by considering whether the addition of a shaft brush to an inverter-fed motor in a Class I hazardous location makes the system more safe or less safe.