A main switchboard synchronizing panel is fitted with two synchronizing lamps and a synchroscope. When paralleling, if the synchroscope pointer is at the noon position and one synchronizing light is bright while the other remains dark, what does this indicate?

Correct Answer: Option D — the generators are out of phase sequence and one lamp is burned out

Synchronizing lights using dark and bright methods indicate phase rotation. If the synchroscope reads noon but one light is bright while another is dark, the phase sequence is incorrect and a lamp filament has failed, violating proper parallel connection prerequisites per IEEE 45 standards.