How, When & Why are power system engineers required to provide a second level of overcurrent protection in the same relay when one layer of overcurrent protection can do the job.? The case in the question involves a bus outgoing feeder and a buscoupler and the bus normal oprating voltage is 10kV. The question came to my mind as it became pretty troublesome while coordinating it with further upstream relays where the client had already provided their relay settings and changes would be required in further upstream relays.