What is the indication on the switchboard of...

What is the indication on the switchboard of...

Question 1 of 270705eccefa4bacbc34ba4d483cb

What is the indication on the switchboard of a ground on a particular phase of an ungrounded three-phase low voltage distribution system?

Question 1 of 27070

Q

What is the indication on the switchboard of a ground on a particular phase of an ungrounded three-phase low voltage distribution system?

🔍 Key Concepts

• Ungrounded three-phase systems and how a single line-to-ground fault affects current and voltage indications • Purpose and operation of ground detector lights on a switchboard • Difference between what wattmeters measure (power) vs what voltage/ground indicators show

💭 Think About

• In an ungrounded three-phase system, what happens to the phase-to-ground voltages if one phase becomes grounded? Think about which phase’s voltage to ground changes and how the other two phases are affected. • Ask yourself: does a single ground on one phase necessarily increase or decrease total power (wattmeter reading), or is it more likely to change an indication designed specifically to detect grounds? • Consider what each instrument on the switchboard is meant to indicate: which one is specifically intended to show a ground fault rather than load changes?

✅ Before You Answer

• Verify what a ground detecting light (or ground detector lamp set) is wired to measure in an ungrounded three-phase system. • Check whether a wattmeter would clearly show a single ground fault if the load has not otherwise changed. • Confirm how an ungrounded system behaves: one phase solidly grounded makes that phase’s voltage to ground go to approximately zero, and the other two phase-to-ground voltages shift. How would that affect a lamp connected from each phase to ground?