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 1.5-2.0 ohms (all others) is normal resistance with rotor at room temperature. Readings above 3.5 ohms indicate high resistance and rotor replacement may be necessary. If reading is 1.7 ohms (100 amp.) or 1.5 ohms (all others) or less, the field coil is shorted.