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American Society of Heating and Ventilating Engineers Guide, 1932 remote from the motor equipment are sometimes found, due to such noises being carried by the steel work, ducts, or piping in the building. There is considerable evidence that these sounds are more easily con trolled with higher motor speeds than with lower motor speeds. Motors which are practically quiet in operation and free from magnetic disturbing noises can be obtained and should always be specified for quietness of operation when used for fan installations in buildings where quietness is a factor. In the construction of fan and motor foundations where the machinery is mounted on the floor or upon a concrete platform, it is a usual practice to install a layer of cork on top of which is laid or floated the base which carries the apparatus. It is essential that the bolts or lag screws which Table 2. Classification of Motors Group Sub. Diy. Ttte Cur rent Speed Char acteristics Starting Torque Starting Current Applications A i Shunt Wound d-c Constant Medium High Fans 2 Squirrel Cage a-c Constant 3 Synchronous a-c Constant 4 Slip Ring or a-c Constant Wound Rotor 5 Double Squir a-c Constant rel Cage Medium Medium Heavy Heavy High -- About Fans, Centrifu six times full gal Pumps load Starts as Squir Motor Genera rel Cage Motor tor Sets, Air Compressors, Fans Low Vacuum Pumps, Air Compres sors Medium Frequent and Heavy Starting Loads, Pumps, Compressors B 1 Brush Shifting a-c Adjustable Medium 2 Cumulative d-c Adjustable Heavy Comp'd with Shunt Predominance 3 Squirrel Cage a-c Multi- Medium Poles can be Speed Regrouped Low High Stokers, Boiler Fans Pumps High Fans, Ice Ma chines C 1 Series d-c Variable 2 Cumulative d-c Comp'd with Series Predominance 3 Slip Ring-- a-c Using External Resistance in Secondary Variable Variable Heavy Heavy Heavy 496 Low / Low / Low Fans Single Acting Reciprocating Pumps Fans Chapter 34--Fans and Motive Power fasten the machines to this foundation shall not extend through to the floor. It is wise to fasten curbs to the floor, these presenting insulated surfaces to the machinery foundation and so preventing it from traveling. The general classification of motors used for heating, ventilation and air conditioning is shown in Table 2. Control for Electric Motors Very small direct current motors may be started by throwing them directly on the line through a suitable starting switch. The larger sizes require some type of starting rheostat. When speed adjustment is desired, the controller for adjusting the speeds of the motor usually functions also as a starting device. Alternating current motors of 5 hp and under, usually may be thrown directly on the line. It is good practice to use a starting switch equipped with a thermal overload or inverse time limit overload device. This type of switch provides protection to the motor beyond the power of fuses to supply. Fuses when used necessarily must be large enough to take care of the inrush current which makes them inadequate for protecting the motor under operating conditions. The thermal overload device allows for this inrush and does not function until an overload has become persistent, the -time element depending upon the percentage of overload over the rating of the element. This type of switch is available for manual operation and also is fur nished in the magnetic type for remote operation by push-button, or for operation by other types of pilots such as pressure switches and ther mostats. On the standard squirrel cage motors above 5 hp a starting compen sator usually is employed to keep the inrush current to within the limits specified by the local power companies. Compensators may be obtained in transformer type and primary resistor type, and usually are furnished for manual operation. They can be secured for remote control also, but are necessarily expensive. However, the new type of high reactance, self-starting motors, may usually be thrown across the line up to 30 hp in size, and still have their inrush current within the limits of the rules of National Electric Light Association. With this type of motor a magnetic contactor usually is used. This device may be operated from a remote point by push-button, if desired. These magnetic contactors are furnished usually with thermal overload and no-voltage protection. For remote operation of motors through magnetic starters, the operat ing buttons may be located in the engineer's or manager's office, and tell-tale indicating lamps may be wired up with the circuit to indicate whether or not the unit is in operation. This type of control is very desirable in large buildings where the engineer is to have complete charge of the ventilating system. Remote or automatic control of the units may be effected also by pneumatic or hydraulic apparatus, or by thermostats or by pressure devices which are provided with electric contacts for starting or stopping the units upon reaching certain conditions. Variable speed slip ring motors and direct current motors may also be arranged for remote speed control by means of pre-set automatic 497