Selective Coordination - Cooper Bussmann

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Selective CoordinationElevator CircuitElevator Circuits and RequiredShunt Trip Disconnect — A Simple Solution.When sprinklers are installed in elevator hoistways, machine rooms, ormachinery spaces, ANSI/ASME A17.1 requires that the power be removed tothe affected elevator upon or prior to the activation of these sprinklers. This isan elevator code requirement that affects the electrical installation. Theelectrical installation allows this requirement to be implemented at thedisconnecting means for the elevator in NEC ® 620.51(B). This requirement ismost commonly accomplished through the use of a shunt trip disconnect andits own control power. To make this situation even more complicated, interfacewith the fire alarm system along with the monitoring of components requiredby NFPA 72 must be accomplished in order to activate the shunt trip actionwhen appropriate and as well as making sure that the system is functionalduring normal operation. This requires the use of interposing relays that mustbe supplied in an additional enclosure. Other requirements that have to be metinclude selective coordination for multiple elevators (620.62) and hydraulicelevators with battery lowering [620.91(C)].There is a simple solution available for engineering consultants, contractors,and inspectors to help comply with all of these requirements in one enclosurecalled the Cooper Bussmann Power Module.Elevator Selective Coordination RequirementIn the 2005 NEC ® , 620.62 states:Where more than one driving machine disconnecting means is suppliedby a single feeder, the overcurrent protective devices in eachdisconnecting means shall be selectively coordinated with any othersupply side overcurrent protective devices.A design engineer must specify and the contractor must install main, feeder,sub-feeder, and branch circuit protective devices that are selectivelycoordinated for all values of overloads and short circuits.To better understand how to assess if the overcurrent protective devices in anelectrical system are selectively coordinated refer to the SelectiveCoordination Section of this booklet. Below is a brief coordination assessmentof an elevator system in a circuit breaker system (example 1) and in a fusesystem (Example 2).Power Module Elevator DisconnectAll-in-One Solution for Three DisciplinesNEC ®• Selective Coordination• Hydraulic Elevators• Traction ElevatorsNFPA 72• Fire Safety Interface• Component MonitoringANSI/ASME A17.1• Shunt TripRequirementThe Power Module contains a shunt trip fusible switch together with thecomponents necessary to comply with the fire alarm system requirements andshunt trip control power all in one package. For engineering consultants thismeans a simplified specification. For contractors this means a simplifiedinstallation because all that has to be done is connecting the appropriatewires. For inspectors this becomes simplified because everything is in oneplace with the same wiring every time. The fusible portion of the switch utilizesLow-Peak LPJ-(amp)SP fuses that protect the elevator branch circuit from thedamaging effects of short-circuit currents as well as helping to provide an easymethod of selective coordination when supplied with an upstream Low-Peakfuse with at least a 2:1 amp rating ratio. More information about the CooperBussmann Power Module can be found at www.cooperbussmann.com.Using the one-line diagram above, a coordination study must be done to seethat the system complies with the 620.62 selective coordination requirement ifEL-1, EL-2, and EL-3 are elevator motors.Go to the Selective Coordination section for a more indepth discussion on howto analyze systems to determine if selective coordination can be achieved.104 ©2005 Cooper Bussmann
Selective CoordinationElevator CircuitExample 1 Circuit Breaker SystemIn this example, molded case circuit breakers (MCCB) will be used for thebranch and feeder protective devices and an insulated case circuit breaker(ICCB) will be used for the main protective device.1,000800600Example 2 Fusible SystemIn our second example, LPJ-(amp)SP fuses will be used for the branchprotection, LPS-RK-(amp)SP fuses will be used for the feeder protection, andKRP-C-(amp)SP fuses will be used for the main protection.1,000800600400300200400300200KRP-C-1600SP10080601600A ICCB1008060LPS-RK-400SPTIME IN SECONDS40302010864321.8.6.4.3400A MCCB200A MCCB100A MCCBTIME IN SECONDS40302010864321.8.6.4LPS-RK-200SPLPJ-100SP.2.3.2.1.08.06.04.03.1.08.06.04.02.03.01.021002003004006008001,0002,0003,0004,0006,0008,00010,000BLACKOUT(PARTIAL)CURRENT IN AMPERES20,00030,00040,00060,00080,000100,000BLACKOUT(TOTAL).011002003004006008001,0002,0003,0004,0006,0008,000CURRENT IN AMPERES10,00020,00030,00040,00060,00080,000100,000Looking at the time current curves for the circuit breaker in the figure above,where any two circuit breaker curves overlap is a lack of selectivecoordination. The overlap indicates both devices open. If any fault currentgreater than 750A and less than 3100A occurs at EL-1, EL-2 or EL-3, the200A circuit breaker will open as well as the 100A branch circuit breaker - thisis not a selectively coordinated system and does not meet the requirements of620.62. This lack of selective coordination could result in stranding passengersin elevators or not having elevators available for fire fighters. Fault currentsabove 3100A will open the 400A circuit breaker as well and faults aboveapproximately 16,000A will open the 1600A circuit breaker - which furtherillustrates the lack of coordination. For a better understanding of how toassess circuit breaker coordination, see the section on Circuit BreakerCoordination in this book. A system that is not in compliance may result inneedlessly stranding passengers and creating a serious safety hazard.To verify selective coordination, go no further than the Fuse Selectivity RatioGuide in the Fuse Selective Coordination section in this book. The Low-Peakfuses just require a 2:1 amp rating ratio to assure selective coordination. Inthis example, there is a 4:1 ratio between the main fuse (1600A) and the firstlevel feeder fuse (400A) and a 2:1 ratio between the first level feeder fuse andthe second level feeder fuse (200A). As well, there is a 2:1 ratio between thesecond level feeder fuse and the branch circuit fuse (100A). Since a minimumof a 2:1 ratio is satisfied at all levels for this system, selective coordination isachieved and 620.62 is met.As just demonstrated in the prior paragraph, the fuse time current curves donot have to be drawn to assess selective coordination. For illustrativepurposes, the time current curves for this example are shown above.©2005 Cooper Bussmann105
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Selective Coordination - Cooper Bussmann

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