In the illustrated switchboard, what is the...

🔍 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.

In the illustrated switchboard, what is the purpose of the device labeled "AM Sel. Sw."? Illustration EL-0003

it allows the instantaneous difference between individual three phase legs to be displayed on the ammeter

it allows the instantaneous average of the three phase legs of alternator current to be displayed on the ammeter

it allows the instantaneous difference between the average of the three phase legs of both alternators to be compared

it allows the individual three phase legs of alternator current to be displayed on the ammeter by selective switching

🔍 Key Concepts

💭 Think About

✅ Before You Answer