🔍 Key Concepts

• Normal vs emergency power sources shown on the one‑line diagram (SSDGs on the main switchboard vs EDG on the emergency switchboard). • How the 480 VAC emergency bus can be fed in different modes (from the main switchboard through a bus‑tie, or directly from the EDG). • What equipment the emergency diesel generator (EDG) is designed to supply in emergency mode according to the diagram (emergency power panels, lighting, etc.).

💭 Think About

• On the diagram, trace the path of power in normal operation: from which generators, through which breakers, to the 480 VAC emergency bus. • Then trace the path of power when the main-emergency bus-tie breaker is open and the EDG is running: which buses and panels are still energized? • Look at every symbol connected to the shore power and EDG and ask: does the diagram actually show what the choice claims (automatic start, shore power restriction, or which buses are fed)?

✅ Before You Answer

• Verify which side of the main-emergency bus-tie circuit breaker the 480 VAC emergency bus is connected to, and what happens if that breaker is opened. • Check whether the EDG output connects to the same 480 VAC bus that feeds the group control centers, or only to specifically labeled emergency power panels. • Confirm whether there is any indication on the diagram that shore power depends on the vessel being tied up on a particular side (port or starboard) — diagrams usually show electrical, not mooring, limitations.