USCG Exam PracticeElectrical troubleshooting and maintenance
On a vessel with an ungrounded (delta) shipboard power system, the ground-detection lamps indicate that one phase lamp is noticeably dimmer than the other two. What does this condition indicate?
- A. The system neutral is properly bonded to the hull
- ✓ A ground fault exists on the phase whose lamp is dimCorrect
- C. The lamp filament on the dim phase is beginning to fail
- D. An overload condition exists on the two brighter phases
Why B is correct
DOE-HDBK-1011 Vol.4 §15-3 explains that in an ungrounded delta system using three ground-detection lamps (one per phase to ground), a ground on one phase dims that phase's lamp and brightens the others, signaling the watchstander to locate the fault.