USCG Exam PracticeElectrical troubleshooting and maintenance
On a vessel with an ungrounded delta power system, the ground-detection lamp associated with a faulted phase will display which indication?
- A. It will extinguish completely while the other two lamps remain at normal brightness
- ✓ It will dim while the lamps on the other two phases brightenCorrect
- C. All three lamps will brighten equally, indicating increased system voltage
- D. It will flash intermittently while the other two lamps remain steady
Why B is correct
DOE-HDBK-1011 Vol.4 §15-3 explains that in an ungrounded system using three ground-detection lamps (one per phase to ground), a ground fault on one phase dims that phase's lamp and brightens the others, signaling the watchstander to locate the fault.