UL 845-2021 pdf download

UL 845-2021 pdf download.Motor Control Centers.
3 Definitions 3.1 For the purposes of this standard, the fllowing apply. 3.2 auxiliary devices – types of devices such as indicating meters (instruments), current transformers, control devices, control relays, timers, protective relays or protective devices, communications devices, etc. 3.3 available short-circuit current – the short- circuit current available at the equipment line terminals plus any motor contribution. The available ac short-circuit current is expressed in rms symmetrical A. 3.4 bus, horizontal – a bus that extends through a motor control center section. 3.5 bus, vertical – a bus that serves the units in a section and that originates from the horizontal bus. This bus may be replaced by insulated wiring. 3.6 Class I motor control centers – mechanical groupings of combination motor control units, feeder- tap units, other units, and electrical devices arranged in an assembly. (See Annex H). 3.7 Class II motor control centers – a Class I motor control center provided with manufacturer- furmished electrical interlocking and wiring between units, as specifically described in overall control system diagrams supplied by the user. (See Annex H). 3.8 combination controller unit – a control unit containing a magnetic or solid-state controller and an externally operable disconnecting means and overcurrent protection. The controller may or may not contain motor overload protection. 3.9 combination motor control unit – a control unit that contains components that perform the following functions: externally operable circuit-disconnecting means, motor branch-circuit overcurrent protection, motor overload protection, and motor control. NOTE Two sets of extemally operable circuit-disconnecting means, each with branch-circuit overcurrent protection and motor controller, may be mounted in a single compartment to form a dual unit. 3.11 feeder-tap unit – a unit that includes an externally operable circuit-disconnecting means and branch-circuit overcurrent protection, principally used for non-motor loads. NOTE Two sets of exterally operable circuit means, each with branch-circuit overcurrent protection, may be mounted in a single compartment to form a dual unit. 3.12 incoming supply conductor – a conductor insalled to provide power to the equipment. 3.13 main bonding jumper – the connection between the grounded circuit conductor and the equipment grounding conductor at the service. 3.14 motor control center – a floor-mounted assembly of one or more enclosed vertical sections typically having a horizontal common power bus and principally containing combination motor control units. NOTE Usually. units are mounted one above the other in the vertical sections. The sections nomally incorporate vertical buses connected to the common power bus, thus extending the common power supply to the indvidual units. Power may be supplied to the individual unis by bus bar connections, by stab connections, or by suitable wing. 3.15 motor control center section – the vertical enclosure and assembly that is prevented by the structural framework from being physically separated into smaller parts and is intended to receive individual combination motor control units. The function of the vertical section is to support the horizontal and vertical buses, units, covers, and doors when the doors are not mounted directly to the unit. 3.16 service equipment一the necessary equipment, usually consisting of a circuit-breaker or switch and fuses, and their accessories, located near the point of entrance of supply conductors to a building or‘ other structure, or an otherwise defined area, and intended to constitute the main control and means of cut-off of the supply.
5.4 Short-circuit 5.4.1 Standard short-circuit current ratings of motor control center units 5.4.1.1 Each unit of a motor control center containing a short-circuit protective device shall be assigned a short-circuit current rating. Except for units containing only control-circuit components, the rating shall be the applicable rating from Table 2. 5.4.1.2 Each unit of a motor control center containing only control-circuit components shall be assigned a short-circuit current rating not greater than the interrupting rating of the short-circuit protective device, but not exceeding 100 kA. 5.4.1.3 A unit not containing any short-circuit protective device shall not be connected directly to the power bus (with the exception of lightning and surge arresters) and shall not be assigned a short-circuit current rating, which shall be indicated as “NA.” Absence of a short-circuit current rating on such a unit does not affect the short-circuit current rating of the motor control center. 5.4.2 Combination motor control units A combination motor control unit, for other than variable speed drives, may have a short- circuit current rating greater than the short-circuit current rating of any individual component if evaluated by design tests. For combination motor control units containing variable speed drives the short circuit current rating shall not be greater than the interrupting rating of the short-circuit protective device. When the short-circuit protective device is an instantaneous-trip circuit breaker, it shall be evaluated by design tests.UL 845-2021 pdf download.