I've been taught that bond bushings are required on the secondary side of the transformer because ground fault currents on a metallic conduit between the transformer and the main breaker on the low voltage panel would bypass the secondary protection and rely on current ramped up by inductance on the primary side to open up the primary protection. And, since more time is consumed to ramp up sufficient fault current through induction, every effort must be made to minimize impedance on any ground path encountered before the secondary protection, which would be the metallic conduit serving the 208 volt panel and the panel can itself.
Can anyone tell me if I'm off-base here? Not that I'm opposed to bond bushings on any conduit, but if the metallic conduit for the transformer's primary conductors is effectively bonded, no bond bushing are required. Effectively bonded meaning tight locknuts on standard EMT fittings. After 22 years in the trade and boatloads of transformers one would think I wouldn't be second guessing the methods I've used and the theory I've been taught, but I want to bounce this off you guys 'cause the subject came up at work today and apparently I'm the only one that believes that although bond bushings are a good idea everywhere, there's no requirement for them on a metallic conduit containing the primary conductors of a transformer.
Let's here it...
Can anyone tell me if I'm off-base here? Not that I'm opposed to bond bushings on any conduit, but if the metallic conduit for the transformer's primary conductors is effectively bonded, no bond bushing are required. Effectively bonded meaning tight locknuts on standard EMT fittings. After 22 years in the trade and boatloads of transformers one would think I wouldn't be second guessing the methods I've used and the theory I've been taught, but I want to bounce this off you guys 'cause the subject came up at work today and apparently I'm the only one that believes that although bond bushings are a good idea everywhere, there's no requirement for them on a metallic conduit containing the primary conductors of a transformer.
Let's here it...