Rotor Test

Test rotor for grounded, open or shorted field coils using an ohmmeter. Test for grounds between slip rings and rotor shaft; no continuity should exist. Check for an open field by connecting ohmmeter across slip rings, 1.7-2.1 ohms (100 amp.) or 1.5-2.5 ohms (all others) is normal resistance. Readings above 3.5 ohms indicate high resistance and rotor replacement may be necessary. If reading is 1.7 ohms (100 amp.) or 3 ohms (all others) or less, field coil is shorted.