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The act of isolating a faulted circuit from the remainder of the electrical system, thereby eliminating unnecessary power outages. The faulted circuit is isolated by the selective operation of only the overcurrent protective device closest to the overcurrent condition.
Without Selective Coordination With Selective Coordination
The proper localization of a fault condition to restrict outages to the equipment affected, accomplished by the choice of selective fault-protective devices.
Selective Coordination - Insulated Case Circuit Breakers (See SPD)
Selective Coordination - Insulated Case Circuit Breakers (See SPD)
2000A Insulated Case Circuit Breaker STD Is an Option - Allows breaker to delay opening Instantaneous Override built-in: may be as low as 12X the breaker rating Will often result in lack of coordination
Selective Coordination - Insulated Case Circuit Breakers (See SPD)
Selective Coordination - Insulated Case Circuit Breakers (See SPD)
2000A Insulated Case with STD and Instantaneous Override and 100A Molded Case Thermal Magnetic Circuit breaker - NO Coordination in Short-Circuit Region (above 21,000A)
IEEE 242-1986 “BUFF BOOK”Protection and Coordination of Industrial and Commercial Power Systems
Page 263 6.4.1 Protection (Series Connection). It should be noted that selectivity will not be provided at any current level where the breaker trip characteristic curves overlap when this protection scheme is used, that is, both circuit breakers will trip.
IEEE 242-1986 “BUFF BOOK”Protection and Coordination of Industrial and Commercial Power Systems
Page 528 Coordination 14.2.2
Coordination can easily be achieved with low voltage current-limiting fuses that have fast response times. Manufacturer’s time current curves and selectivity ratio guides are used for both overload and short-circuit conditions, precluding the need for calculating time intervals.
IEEE 141-1993 “RED BOOK” Electrical Power Distribution for Industrial Plants
Page 256 5.7.2.3 Low-voltage circuit breakers. To achieve this level of selectivity, power circuit breakers utilize short-time delay trips. The equipment protected by this breaker must be designed to handle the available short-circuit current for the duration of the short-time delay.
IEEE 242-1986 “BUFF BOOK”Protection and Coordination of Industrial and Commercial Power Systems
Page 528 Coordination 14.1 A coordination study or revision of a previous study may be needed for an existing plant when new loads are added to the system or when existing equipment is replaced with higher rated equipment.
IEEE 602-1996 “WHITE BOOK”Electrical Systems in Health Care Facilities
Page 57/58 3.7.1.1 Protection requirements. As total selectivity and maximum safety to personnel are critical, a total short-circuit coordination, and component protection study shall be performed.
IEEE 141-1993 “RED BOOK” Electrical Power Distribution for Industrial Plants
Page 256 5.7.2.3 Low-voltage circuit breakers. It should be recognized that providing selectivity to the load-side devices may result in equipment bus structures being underprotected. The Standards for such equipment, ANSI/UL 891-1984 [B21] for switchboards, ANSI/UL 845-1987 [B20] for motor control centers,
IEEE 1015-1997 “BLUE BOOK” Applying Low-Voltage Circuit Breakers Used in Industrial and Commercial Power Systems
Page 135 5.5.4 Short-time delay
All MCCBs and most ICCBs with a short time delay have an instantaneous override. If selective coordination is required for fault currents above the instantaneous override level, a power circuit breaker defined as an LVPCB with a short-time delay option, as shown in Figure 5-16, should be considered.
IEEE 242-1986 “BUFF BOOK”Protection and Coordination of Industrial and Commercial Power Systems
Page 252 6.3 Trip Unit The resulting combination of long-time delay and short-time delay characteristics provides delayed tripping for all levels of overcurrent below the instantaneous response. This provides time for downstream circuit breakers to operate and clear the fault. The withstand of other electrical components in the current path should be checked to be certain they can handle the additional stress associated with the longer clearing time.
IEEE 1015-1997 “BLUE BOOK” Applying Low-Voltage Circuit Breakers Used in Industrial and Commercial Power Systems
Page 62 3.38 Series-connected rating. Sometimes it is erroneously thought that series combinations are at a disadvantage with regard to coordination as compared to fully rated systems. The fact is that even fully rated circuit breakers with instantaneous trips will not “coordinate” once the fault level exceeds both circuit breakers’ instantaneous trip levels.
IEEE 1015-1997 “BLUE BOOK” Applying Low-Voltage Circuit Breakers Used in Industrial and Commercial Power Systems
Page 134 5.5.3 Series MCCBs
Selective coordination is limited to currents below the instantaneous pickup of the line-side circuit breaker. For any fault downstream of the load-side MCCB having a current greater than the instantaneous pickup of the line-side MCCB, both circuit breakers trip, and power is interrupted to unfaulted circuits fed by the line-side circuit breaker.