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MANAGERS AND PROJECTIONISTS 511
commutator, and perhaps a new armature coil or coils as well.
GENERAL INSTRUCTION NO. 8.— Before starting the machine see that it is perfectly clean and that the brushes move freely in their holders and make good contact with the commutator. Also make sure that all connections are tight.
GENERAL INSTRUCTION NO. 9.— Bearings run hot. The first rule when a bearing runs hot is to see that the oil well is filled with good clean oil and that the oil-rings run freely, carrying the oil to the shaft. If a bearing runs hot on a new machine, shut down and wash it out with kerosene. The trouble is probably due to dirt that has accumulated in shipment. If the bearing has been running along satisfactorily and suddenly gets hot, flood the well with clean oil, leaving the drain cock open and pouring in the clean oil while the machine is running, to free the bearing from dirt. A change to a different grade of oil, either heavier or lighter, will often correct a bearing trouble of this kind. Never use water to cool a bearing. It may get into the insulation of the windings and cause worse trouble A machine with clean oil of the proper grade never gives trouble from hot bearings.
GENERAL INSTRUCTION NO. 10.— Heating. Many projectionists, who handle motor generator sets and are not posted as to the permissible operating temperatures of same, become alarmed when some part or parts of the apparatus feel very hot to the touch.
The fact that a motor or generator, or parts thereof, feel quite hot to the touch does not necessarily indicate an unsafe condition.
To determine the actual state of affairs, proceed as follows: The projection room should be equipped with a good thermometer with a centigrade scale, though a Fahrenheit scale can be made to serve, provided it will register not less than 200 degrees.
The American Institute of Electrical Engineers advises, in its standardized rules, a permissible maximum actual temperature of 90 degrees C, which is equal to 194 degrees Fahr., as the limit of safe operating temperature for motor or generator parts, or for transformer coils, et cetera. This means that inasmuch as the ordinary temperature of the human body is about 98 degrees Fahr. (blood temperature) 194 degrees Fahr. would be very hot to the touch.