Excessive Heating of Body & Bearing

While the machine is on bed, carefully record, with a thermometer the temperature of the hottest area on the stator body, and of the bearing housing if accessible. The temperature of the body will be found to vary, being hottest over a place where the body is in contact with the stamping through the ribs provided on the inner surface of the body. A temperature RISE of 40oC above the ambient temperature indicates no abnormality. But more important than this is any sign o sudden increase in the temperature rise recorded previously. Ignoring the slight changes that will occur due to variation of the ambient temperatures, If the rise exceeds 40oC on the body, an excess current due to either overloaded or under voltage, or inadequate cooling/ventilation is indicated. Reduce the load in such cases until rectification is effected, or other wise the insulation may suffer premature ageing. If the excess rise is only in certain areas of the body, a likely reason may be the overloading of one or two phases due to single phasing, i.e., operation with voltage supplied to only two out of the three stator phases. If this is the case, the fault may lie perhaps not in the motor itself but in the stator switch or elsewhere, in the form of a weak contact or loss of continuity. This must be discovered and set right immediately. If the temperature RISE of the bearing housing exceeds 50oC, then there is either too little lubricant or, which is more common, too much lubricant (grease or oil) in the bearing housing; in either case remove the external bearing cap, ascertain the cause and make the appropriate rectification. See also Inspection and checking of bearing.