The Diseases Of Electrical Machinery

48 THE DISEASES OF hindered from moving, and may not convey up enough oil to the journal. The oil rings should be of brass (cut off from drawn brass tube, carefully cleaned from grit). Iron is objectionable, because of magnetic effects, and zinc is also bad, since it is so easily rubbed away. A fault which often occurs with new plant is the belt being stretched too tight. This cannot be sufficiently strongly impressed, since a too tight belt may melt out a bearing in next to no time. This occurrence may be prevented by gradual tightening of the belt. Since, however, mishaps often occur from this cause, it is obvious that sufficient attention is not always paid thereto. Cutting-off of the Air Supply.—When working continuously, a motor requires a good supply of air, and a common cause of abnormal heating of a motor is the hindering of the supply by covering the motor with a case. Only when motors are intermittently at work is such a covering allowable. For continuous working it is dangerous for the motor. Any casing over the motor should have sides and top of perforated metal ; except in the case of motors in mines, or in places where the atmosphere is explosive, totally- enclosed motors should not be tolerated. We must now refer to a fault which is caused directly by the neglect or forgetfulness of an employé. When stopping a motor, even if only for a short time, the starter handle wiust always be brought back to the