🔍 Key Concepts

• Ground fault (grounded field coil) in an AC motor and what it means electrically • Typical use and purpose of a megohmmeter ("megger") versus other test instruments • How insulation resistance to ground is normally checked on shipboard electrical equipment

💭 Think About

• Which instrument is specifically designed to test insulation resistance to ground rather than just continuity or current flow? • On a ship, when you suspect a winding is grounded to the frame, what kind of test do you need to perform: visual, continuity, or high-resistance insulation test? • Think about which choice is normally used by marine electricians to check if windings are shorted to ground rather than shorted turn-to-turn.

✅ Before You Answer

• Be clear on the difference between checking insulation to ground and checking for shorted turns within a winding. • Consider which device can safely apply a higher DC test voltage to measure very high resistance to ground on large motors. • Eliminate any tools that are mainly for indicating small currents or doing simple visual checks rather than formal insulation resistance tests.