Document 2RvJBLaJwzoJwgzeOLoKgkbVr

872 CHAPTER 57 1965 Guide And Data Book are voluntary.- Those for electrical equipment used in the air:-, conditioning and refrigerating industries are listed in Chapter 71. Of special importance in the United States and Canada are the National Electrical Code (NEC) and the' Canadian Electrical Code, Fart I, respectively. The National Electrical Code is Volume 5 of the National Fire Protection Code, and contains the minimum recommenda tions considered necessary to make electrical installations and equipment safe. All interested industry organisations, insur ance and enforcement groups, and the public are represented on the committees preparing and revising this code, to fulfill permanent-split-capacitor motors are suitable for compressors requiring medium or low starting torques. Capacitor-startand special split-phase motors develop high starting torque. Per formance characteristics are given in Table 4. Domestic refrigerators may or may not have a mechanical air moving device. Those that do generally employ a shadedpole motor. (See Table 4.) Because of their hermetic design, it is neither possible nor necessary to service compressor motors. On the other h*ndF fan motors are accessible and must be occasionally serviced in accordance with manufacturer's instructions. the requirements necessary for adoption by the Ameri can Standards Association. The National Electrical Code is Motor Control not mandatory. Mandatory status is obtained only when it is Starting Switches. To start a single-phase induction motor made part of local ordinances or.by the regulations-offin- of the split-phase or capacitor-start type, a switch is needed surance companies. The electrical .codes-of-practically all - to disconnect the starting winding or the capacitor circuit after communities in the United States are based upon it. Underwriters' Laboratories, Inc., is a, non-profit organiza the motor has been accelerated to approximately 70 percent of synchronous speed. tion sponsored by the National Board of fire Underwriters, In open type motors, centrifugal switches are used and which promulgates standards for various types of equipment. operate at predetermined motor speeds. In hermetic com Underwriters' standards for electrical equipment cover con pressors, electrical arcing cannot be tolerated. Therefore, struction and performance for the safety of such equipment, switches in motors for hermetic compressors must be her and interpret requirements to insure compliance with the metically-sealed, or they must be located outside the com intent of the NEC. A complete list of available-standards - pressor shelL Economic considerations have frequently led to may be obtained from Underwriters' Laboratories which also the use of external switches. examines and tests equipment and publishes lists of equip ment which has passed these tests and therefore bears the Starting Relays. Both magnetic and thermal relays are alum used for starting split-phase motors. They are located outside U/L labels. The lists and labels are recognized by local authorities. the compressor shell. Relays usually respond to the current in the main winding, in order to take advantage of the main The Canadian Electrical Code, Part I, is a standard of the Canadian Standards Association. It is also a voluntary code winding current vs speed characteristics of the motor. The current-speed curve varies with line voltage, so that the with minimum requirements for electrical installations in starting relay must be selected for the range of voltage likely buildings of every kind. The Canadian Electrical Code, Part. II, contains specifica to be encountered in service. Ratings established by the com pressor manufacturer in cooperation with the motor manu tions for construction and performance of electrical equip facturer should not be changed because this may result in ment in compliance with Part I. Specifications for different undesirable starting characteristics. materials and equipment have been published, and the The starting methods by use of relays are: complete list may be obtained from the Canadian Standards Association. Underwriters' Laboratories standards and stand ards of the Canadian Standards Association for electrical equipment are similar so that equipment designed to meet the requirements of one code may also meet the require ments of tiie other. However, there is not complete agreement between the codes and consequently individual standards must be checked when designing equipment for use in both countries. Approvals Laboratories of the Canadian Standards Associ ation examine and test material and equipment for compli ance with the Canadian Electrical Code. Copies of electrical standards may be obtained directly from tire sponsoring organizations. (See Chapter 71.) DOMESTIC REFRIGERATION Motors used in domestic refrigeration range from approxi 1. Starting method using thermally-operated relay. When the motor is started, a contact which is normally closed applies power to the starting winding. A thermal element which controls these contacts is in series with the motor and carries line current. Due to the current flow through this element, it is heated until, after a definite period of time, it is warmed sufficiently to open the con tacts ana remove power from the starting winding. The running current then heats the element enough to keep the contacts open. The setting of the time for the starting contacts to open is de termined by tests on the system components, Le., the relay, the motor, ana the compressor, and is based on a prediction of the amount of time delay required to bring the motor up to speed. 2. Starting method using current-operated relay. In type of connection, a relay coil carries the line current going to the motor. When the motor is started, the inrush^current to the running winding, passing through the relay co3, causes the contacts to close, ana applies power to the starting winding. As the motor comes up to speed, the current decreases until at a definite cali brated value of current corresponding to a preselected speed, the magnetic force of the coil diminishes to a point which allows the contacts to open to remove power from the starting winding. mately 1/100 hp fan motors to hp compressor motors. These motors are in most cases controlled directly by-the Motor Protection system controls, which may be thermostats, timers, pressure switches,-or other automatic control devices. Practially all standard production motors in the United States and other countries are single-phase motors, for operation on 115'and 230 volts single-phase a-c. Motors for domestic refrigerator and freezer compressors are protected by thermal protectors mounted directly on the outside of the compressor shell. These protectors carry the full motor line current The protector size is based on a contact rating which is adequate to interrupt the stalled current of Motors the motor on continuous cycling. Cycling-life requirements are based on specifications established by Underwriters' Labora Compressor motors in most domestic refrigerators are tories in the United States and the Canadian Standards As hermetically-sealed. They are either split-phase, .capacitor- sociation in Canada. Both standards require 15 days of con start, or pennanentieplitHjapacitor # motors. Split-phase and tinuous cycling and a 72-hour heating test with locked rotor. Motors and Motor Protection - Table A .... Characteristics of Various Types of Single-phase a-c Motors SptH-Pbam Gcnrof-hupM* - Spill-Photo Htgh-Siart , Spfit-Capoccfor CepotHor-Slert tadixhoo-Roa Shodod-Polo Connection diagram i* j J, S START J IRUR 1 > CAP"~ S START 1 LsD RIM^ Capodtor-Start Cqpcctlor-Jlaa ' p--L-ii-<>(RUM Speed torque curves -------- Combined windings -------- Run winding Starting method HP ratings Full load speeds at 60 cycles Torque . Locked rotor Breakdown Speed classification Full load power factor A' $A / d 7 s! est Relay Yw-H 3450-1725 Moderate Moderate Constant Moderate TV Relay V~H 3450-1725 . ITVwAi Vi fXii./ Ji if J!' A /A d & / ( lesr 340? None V*s-o 3450-1725 Relay Vw-J-i 3450-1725 High, ..High ' Constant Low Moderate* Constant Moderate . High Very High High Constant Moderate ) as? None 'Viss-tf - 3100-1550 1000 Low Low Constant or Adjustable Moderate Relay 7*-6 . 3500-1750; High High Constant. High Thermal protectors are responsive to temperature as well as or other automatic devices: Single-phase-motors using 115 electric current. Application is made and protector rating de and 230 standard voltage are most common. termined by the compressor manufacturer in cooperation with the protector manufacturer. Any change in protector rating Motors after the proper application has been made, may* result in either over-protection and frequent trip-out or under-protec-, tion and burn-out of the motor windings. Connections to protector terminals should not be changed ' Most compressor motors for room air conditioners are permanent-spliLcapacitor of capadtor-start, capacitor-run motors in hermetically sealed systems. Permanent-split- and no additional connections should be made to the termi nals, lywwBA any change in the heat added to or removed capacitor motors provide mi economical approach to. the prob^ lem of muint-qining low-current draw on a 115-volt circuit. from the terminal will affect the rating of the protector. Performance data are given in Table 4. Open,-type air-moving motors, which are usually small The necessity for low-current-draw on a.115-volt circuit, fractional horsepower motors, are protected by self-imped makes it necessary to* use permanent-split-capacitor ance, thermostats, or thermal protectors. Shaded-pole motors motors for the fans of room air conditioners. Where current- can be impedance-protected. These motors are designed draw is no'problem, shaded-pole motors are used. liberally with regard to iron, and the high impedance of the Hermetic design makes it impossible and unnecessary to windings is used to limit motor current and, consequently, service compressor motors. Fbn motors are accesible, and winding temperature. (See Underwriters' Laboratories re should be occasionally serviced in accordance with manu quirements for impedance-protected motors.) facturer's instructions. Most air-moving motors are protected by thermostats and thermal protectors, operating in response to motor winding Motor Control temperature, or motor temperature and motor current. The protector is part of the motor itself. The nameplate of the motor is marked in accordance with the requirements of the approval agency. Starting relays and protectors for hermetically-sealed com pressor motors normally do not require any maintenance other than to nudea sure that electrical connections are tight. Protectors for open motors do not require any maintenance. Starting Switches. Permanent-split-capacitor motors do not V require a starting switch, because the starting winding with its capacitor is designed to remain permanently connected to the motor circuit. Capadtor-start induction-run, and ca padtor-start capacitor-run motors, have at least one ca pacitor, which is in the'circuit only during the start.of the motor. Therefore,* it is necessary to disconnect the starting winding or the -starting capacitor as soon as the motor, has ROOM AIR CONDITIONERS reached full speed. *T* Starting Relays. Both thermally-operated and'current- Room air conditioners have compressor motors ranging from $ hp to 3 hp, and fan motors ranging from A hp to $ hp. Motors are in most cases controlled directly by the sys tem controls, such as thermostats, timers, pressure switches, operated relays may be used (see previous section on .Domes tic Refrigeration for a description of these relays).'. io . - Capadtor-start hermetically-sealed motors above hp are usually started with a voltage-type relay. In this! method of