Correct AnswerC. To act as a backup power source during a grid outage
Quick Explanation
A diesel generator set in a commercial building primarily provides backup/standby electrical power when the normal utility/grid supply fails. An automatic transfer system can start the DG and transfer selected essential loads.
Detailed Explanation
Concept & Reasoning
DG sets are sized according to essential/standby load demand, motor starting, transient voltage/frequency performance and code requirements. They are not normally operated solely to reduce daily energy bills unless a specific economic/peak-shaving strategy exists.
How to Solve It in the Exam
DG in buildings = standby power.
Important Exam PointDifferentiate standby generation from UPS: UPS supplies near-instant ride-through; DG provides longer-duration backup after start-up.
Related Revision Path
This question sits in the revision path Building Electrical Services → Standby Power → Diesel Generators .
