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 Froper maintenance must be given careful consideration 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. & regular inspection schedule will practically assure continuous operation. Preventive maintenance will avoid costly repairs. dow 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. “eep 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 aid 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 mili blowing, if necessary. Remove any accumulations of oil or grease with carbon tetrachloride in a well-ventilated room. Make sure there are no foreign materials in the air gap or other air passageways. If the machine is installed in a dirty place, it should be disassembled and thoroughly cleaned as frequently as the conditions warrant. Listen for any mechanical noises which indicate metal-to-metal contact. If present, shut down the machine as soon as possible and check for misalignment or bearing failure. 3-46