🔍 Key Concepts

• Function of an ammeter selector switch (AM Sel. Sw.) on a three‑phase generator switchboard • How many ammeters are shown per generator and what that implies about measuring three separate phase currents • Difference between measuring an average or difference of currents vs. measuring one phase at a time

💭 Think About

• Look at the single ammeter symbol labeled "A" for each panel and trace how the AM Sel. Sw. connects it into the three‑phase system—what does a selector switch normally let you choose? • Ask yourself whether normal shipboard practice is to use one ammeter per phase, or one ammeter with a switch that lets you check each phase individually. • Consider which answer choices talk about "difference" or "average" of currents, and whether the schematic shows any extra devices (like summing or differential circuits) that would be needed for that.

✅ Before You Answer

• Verify that the AM Sel. Sw. has multiple positions leading to the three phase lines feeding the generator, not to another averaging or comparison device. • Confirm from the diagram that there is only one ammeter per generator panel; this hints at why a selector switch is needed. • Eliminate any option that requires the switch to perform mathematical operations (average or difference) rather than simple selection of which current is sent to the meter.