Document ZBa0mZrR4x88pennXabqD3L1V

838 CHAPTER 39 1950. Guide almost entirely by, inrush current limitations. The starting torque of all motors varies with the starting current and it is therefore necessary to insure that the motor is supplied with sufficient current to develop enough torque to accelerate the load. In present practice overload protection of motors is obtained by use of thermal overload inverse time limit type protection. The usual setting of such protection devices is not to exceed 125 per cent of rated full load current'for open 40 C rise motors, and not to exceed 115 per cent of rated full load current for all other motors, the element tripping after a definite interval of time. The National Electrical Code requires the addition of fuses or circuit breakers to protect the overload elements from severe short circuit currents. Two types of protection are available against low voltage at the motor terminals. One type, called low voltage release, permits the motor line contactor to drop out on low voltage and to close again when the voltage returns to. normal, thereby restarting the motor when the abnormal condi tion is ended. The second type, called low voltage protection, causes the motor line contactor to drop out on low voltage, but prevents restarting when- the voltage returns to normal except by the action of an operator. This latter type of protection is desirable where it is necessary for the operator to make initial starting adjustments on the machine. . Manual control for an alternating or a direct current motor is usually located near the motor. When so located an operator must be present to start and stop or change the speed of the motor by operating the control mechanism. Manual control is sometimes employed only as a device to give overload protection and another device is employed to start and stop the motor. Manual, control is used particularly on small motors which operate unit heaters, small blowers, and room coolers in an air conditioning system. In other cases manual control in the form of drums, when used with multi-speed motors, is only, used as a speed setting device, while the starting and stopping functions operate automatically through thermostats and pressure switches.. , Because of the increasing complexity of air conditioning systems, the equipment is operated preferably by automatic control, and less dependence is placed on manual operation and regulation. Automatic control of motor starters , may be accomplished by the use of remote push button stations, by a thermostat, float switch, pressure regulator, or other similari pilot devices. An added advantage of auto matic control is that the main wiring for the,starter may be installed near the motor, while the starter may be operated by a control device located 'elsewhere. . ' TYPICAL MOTOR AND CONTROL SPECIFICATIONS Specification A. Typical Specifications foe d-c Motobs Constant Shunt (1151 ......... Hp,-.;.. .....RPM, Adjustable Speed, Compound Wound, {230 Volts Varying Series (600] d-c Motors for Driving ..................................... (Application). Motor Shall Be Arranged for '. ^. (Horizontal) Mounting and Shall Be Provided with a.................................... (Vertical / (Open, Splashproof, etc.) Type of. Enclosure, ' Insulation, and jg^!vej Bearings. ' Motors and Motor Controls 839; .: Specification. B.' Typical Specifications rou d-c Motob Contbol . Specification C. Typical Specifications fob Sqdibbel-Cage Motobs 208' RPM, {gj} Cycles, Volts, {3} Phase,. 550. ' ' Squirrel-Cage Induction Motors of-the IVEAfA ' ' {DDeessiiggnn A--Normal B--Normal Starting Torque, Starting Torque' Starting NEMA Current Above NEMA Starting Current . Value) Design C--High Starting Torque, NEMA Starting Current Design D--High Slip High Starting Torque ype . Driving......(.A...p..p..l.i.c..a..t.i.o..n..)...... Motor Shall Be Arranged for 1 vertical j Mounting and Shall Be Provided with a-..... .......... Type of Enclosure, NEMA ... (Open, Splashproof, etc.) . .. {class b} filiation, and {I'ffi''6} Bearings. ** Refer to section on Specification ADlt.e'rnTatyinpgicCaurlreSntpMecotiofriscfaotr eioxpnlasnaftoiobn of typea,'. Wound Rotob * Motobs ................ .-Hp,................RPM, [208] ' ^ . ... .. ~ Cycles,{^1 Volts, Phase, Wound Rotor (55oj Induction Motors for Driving.................... Motor Shall Be Arranged for .... (Application) , Mounting and Shall. Be Provided with a.......................................... (Vertical. (Open, Splashproof, etc.) Type of Enclosure; NEMA {q|^ gjlnsulation and {gj^gve} Bearings. Specification E. Typical Specifications fob Synchbonous Motobs ............... Hp, .:... .RPM, ....... Per Cent P.P., ..!.. . Volts, Phase, Cycles, (Belted Synchronous Motors of the 1 Coupled Type for Driving......................................... (Engine (Application). Motor Shall Be Arranged for {verticS*^} Of)era*'on aQd Shall Be Provided with' a ....... ...Type of Enclosure. Motor Shall Be Capable (Open, Splashproof; etc.) /'