Branch Circuits for Grouped Loads

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3.  The  total  load  on  any  overcurrent  device, located in a panelboard, will not exceed 80 percent of its rating.  If  in  normal  operation,  the  load  will  be continuous (3 hours or more) unless the assembly including  the  overcurrent  device  is  approved  for continuous duty at 100 percent of its rating. Power-distribution   panels   are   similar   to   the feeder-distribution type. They have bus bars normally rated up to 1,200 amperes at 600 volts or less and contain control and overcurrent devices sized to match connected   motor   or   other   power   circuit   loads. Generally, the devices are three-phase. Special   panelboards.   containing   relays   and contactors, can be obtained and installed when remote control of specific equipment is specified. A thorough knowledge  of  all  the  available  types  of  panelboards aids in the selection and installation of the proper unit. Service-equipment  panelboards,  for  loads  up  to 800 amperes, containing six or fewer main fused switches,  fused  pullouts,  or  circuit  breakers  are available. These panels constitute service equipment and frequently contain split buses that supply branch circuit or feeder overcurrent devices installed in the same enclosure (figs. 5-4 and 5-6). Feeder  distribution  panels  generally  contain circuit overcurrent devices rated at more than 30 amperes to protect subfeeders that extend to smaller branch-circuit  panelboards. BRANCH CIRCUITS FOR GROUPED LOADS The uses and limitations of the common types of branch  circuits  are  outlined  in  the  Summary  of  Branch- Circuit  Requirements  (NEC®  table  210-24).  Lighting branch circuits may carry loads as high as 50 amperes, although florescent lighting is limited to use on circuits of 15-ampere or 20-ampere rating. Such circuits are extensively   used   in   commercial   and   industrial occupancies.  Branch  circuits,  supplying  convenience outlets for general use in other than manufacturing areas, are usually limited to a maximum of 20 amperes. The  type  of  outlet  required  for  heavier  capacity  circuits usually will not accommodate the connection plug found on portable cords, lamps, motor-driven office machinery, and so forth. INDIVIDUAL BRANCH CIRCUITS Any   individual   piece   of   equipment   (except motors) also may be connected to a branch circuit meeting the following requirements: Conductors must be large enough for the individual load supplied. Overcurrent protection must not exceed the capacity of the conductors or 150 percent of the rating of the individual  load  if  the  single-load  device  is  a  nonmotor- operated  appliance  rated  at  10  amperes  or  more.  Only  a single outlet or piece of equipment may be supplied. MOTOR BRANCH CIRCUITS Because  of  the  peculiar  conditions  obtained  during the starting period of a motor and because it may be subjected  to  severe  overloads  at  frequent  intervals, motors, except for very small sizes, are connected to branch circuits of a somewhat different design from that  previously  discussed. CONDUCTORS The   Code   covers   general   requirements   for conductors  and  their  type  designations,  insulations? markings, mechanical strengths, ampacity ratings, and uses. These requirements do not apply to conductors that form an integral part of the equipment, such as motors, motor controllers, and similar equipment, or to conductors specifically provided for elsewhere in the Code. Conductors  must  be  insulated  except  where covered or bare conductors are specifically permitted by  the  NEC®.  The  Code  covers  the  insulation  of neutral conductors of a solidly grounded high-voltage system. When stranded conductors are installed, the Code  states  that  stranded  conductors  installed  in raceways must be a size No. 8 or larger with the following  exceptions: Exception No. 1: When used as bus bars or in mineral-insulated,  metal-sheathed  cable Exception  No.  2:  When  bonding  conductors  are required Conductors in Parallel Aluminum,  copper-clad  aluminum,  or  copper conductors of size 1/0 and larger, in each phase of the current; neutral; and grounded circuit conductors may be  connected  in  parallel  (electrically  joined  at  both ends to form a single conductor). Exception No. 1: Conductors in sizes smaller than No. l/O AWG will be permitted to run in parallel to supply  control  power  to  indicating  instruments, contactors,  relays,  solenoids,  and  similar  control devices provided: 1.   They are contained within the same raceway or cable 5-8

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