6. When applicable, check the brushes to make sure they ride freely in the brushholders, The brushes were correctly positioned and springs adjusted to the right pressure at the factory. HEATING The rated temperature rise of the machine is stamped on the nameplate. The actual operating temperature of the machine will be the temperature rise of the machine plus the temperature of the surrounding air, Standard Class A insulated machines will withstand an occasional maximum observable temperature of 90°C (194°F) for open machines and 95°C (203°F) for enclosed machines. MAINTENANCE GENERAL Proper maintenance must be given careful considerations if the best performance and longest life are to be expected from the machine. The major features are those of lubrication, care of the insulation, and commutation. A regular inspection schedule will practically assure con- tinuous operation. Preventive maintenance will avoid costly repairs. How often various inspections should be made will depend a great deal upon the type of machine and the conditions under which it is installed and operated. Keep the machine clean. the machine, Do not permit rubbish to accumulate about It may seriously restrict the ventilation of the machine or get into moving parts, and cause a breakdown. With the machine at rest and disconnected from the line, wipe off any accumulation of dust with a dry cloth. The inside of the machine may be cleaned by suction or mild blowing, if necessary. Remove any accumulations of oil or 3-29