Application of shaft bonding devices (brushes) on large inverter fed machines operating in a class I location

Application of unprotected shaft bonding devices (brushes) in hazardous locations are prohibited as they are arcing and sparking devices until they are proven to be not ignition capable under 2017 NEC [1] section 510.125(B)(5). A paper was published in 2014 on a small motor application suggesting a means to determine whether a spark is ignition capable by addressing physics and a methodology to evaluate the relative safety of two example cases. This paper presents the application of a shaft bonding device on a large converter fed machine to validate devices as being nonincendive and therefore are usable in classified locations. Generally testing of a large converter fed motor is a rare occurrence and therefore the authors would like to present such data taken on a synchronous motor rated 23500 kW 9000 Volts 4 pole operating on a converter. The test data is compared with data derived by calculation. Another example of a large induction motor is considered using a similar calculation method. This may help users and manufacturers in applying shaft bonding devices or brushes without further means of explosion protection.