🔍 Key Concepts

• Megohmmeter (insulation resistance tester) operation and what it actually measures • How ground faults in shunt field coils are located in a DC machine • Why you often need to isolate individual components from the rest of the circuit when testing for grounds

💭 Think About

• Think about what happens to the megohmmeter reading if multiple field coils are still electrically connected together—can you tell which single coil is grounded? • Ask yourself: to positively identify which shunt field coil is grounded, do you need the coils to be tested one at a time or all together as a group? • Consider which option directly prevents current paths through the rest of the field circuit that could mask or share the ground fault.

✅ Before You Answer

• Which choice ensures only one coil at a time is in the test circuit when you use the megohmmeter? • Which option is specifically about the shunt field coils themselves, not the frame, hull, or main line leads? • Which action would most clearly prevent parallel paths to ground that would confuse your measurement?