Shaft-Bonding Devices: Application on Large Inverter-Fed Machines Operating in a Class 1 Location

Until they are proven to be not ignition capable under the 2017 National Electric Code (NEC), section 510.125(B)(5) [1], the application of unprotected shaftbonding devices (brushes) in hazardous locations was prohibited because they are arcing and sparking devices. A paper was published in 2014 on a small motor application that proposed a way to determine whether a spark is ignition capable and a methodology for evaluating the relative safety of two example cases [4]. This article presents the application of a shaft-bonding device on a large converterfed machine to validate devices as being nonincendive and, therefore, usable in classified locations. The testing of a large converter-fed motor is a rare occurrence. The authors present data taken on a synchronous motor (rated 23,500 kW, 9,000 V, four poles) operating on a converter. The test data are compared with data derived by calculation. Another example of a large induction motor is considered with a similar calculation method. This may help users and manufacturers to apply shaft-bonding devices or brushes without further means of explosion protection.