USCG Exam PracticeElectrical measuring devices and instrumentation
On a shipboard ungrounded delta distribution system, the ground-detection lamp associated with a faulted phase will:
- A. Brighten, while the lamps on the unfaulted phases dim
- B. Extinguish completely, while the lamps on the unfaulted phases remain unchanged
- ✓ Dim or go out, while the lamps on the unfaulted phases brightenCorrect
- D. Flicker at the system frequency, indicating the location of the fault
Why C is correct
In a three-lamp ground-detection scheme on an ungrounded system, all lamps normally glow equally. A ground on one phase reduces that phase's voltage-to-ground toward zero, dimming or extinguishing that lamp, while the other two phases see elevated voltage-to-ground, brightening their lamps.