🔍 Key Concepts

• Relay/contactor coil faults: difference between an open coil and a shorted coil • How ohmmeters and meggers behave when measuring shorts vs opens • What visual and fuse indications usually tell you about overcurrent or short circuits

💭 Think About

• Think about what electrical resistance you expect if many turns of a coil become shorted together inside the winding—does that make the resistance very high, very low, or unchanged? • Which instrument (ohmmeter vs megger vs voltmeter) is best suited to detect a direct short inside a coil winding? • If a coil is shorted, how would the current and heating change, and what physical or protective-device signs might you see?

✅ Before You Answer

• Be clear on the difference between zero ohms, infinite ohms, and normal coil resistance on an ohmmeter • Decide what a megger to ground actually tests (insulation to ground, not between turns) • Ask: would a shorted coil usually draw more or less current, and what would that do to insulation and fuses?