selective coordination
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© 2001 Cooper Bussmann, Inc.
Suggestion on How to Use
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• Download both the PowerPoint file (.ppt) and script file (.pdf)
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Selective Coordination
© 2001 Cooper Bussmann, Inc.
Selective Coordination
• For 600 Volts & less
• Easy concept to understand
• Hard to verify, if you do not know what to look for
• Misinterpretations or lack of understanding is very prevalent
• People review curves (hand drawn or computer generated) and they do not know how to interpret
© 2001 Cooper Bussmann, Inc.
Selective Coordination
Definition:
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
Selective Coordination: Avoids BlackoutsSelective Coordination: Avoids Blackouts
OPENS
NOT AFFECTED
UNNECESSARYPOWER LOSS
OPENS
NOT AFFECTEDFault Faul
t
© 2001 Cooper Bussmann, Inc.
Selective Coordination: NEC®
240.2 Definitions
Coordination.
The proper localization of a fault condition to restrict outages to the equipment affected, accomplished by the choice of selective fault-protective devices.
© 2001 Cooper Bussmann, Inc.
Selective Coordination: NEC®
240.12 Electrical System Coordination where orderly shutdown required to minimize hazards
620.62 Selective Coordination required where more than one elevator is supplied by single feeder.
517.17 Selective coordination between main and feeder required for health care facilities where main has GFP (feeder also required to have GFP).
© 2001 Cooper Bussmann, Inc.
Selective Coordination
Chapter 2 Video
Selective Coordination
© 2001 Cooper Bussmann, Inc.
Selective Coordination
Coordination
Circuit Breakers
© 2001 Cooper Bussmann, Inc.
Spring Loaded ContactsLatch
Bimetal
Magnetic Element
Line
Load
Trip BarCircuit Breaker
Operation
© 2001 Cooper Bussmann, Inc.
Spring Loaded ContactsLatch
Bimetal
Line
Load
Trip Bar Thermal Overload Operation
Normal State
© 2001 Cooper Bussmann, Inc.
Spring Loaded ContactsLatch
Line
Load
Trip Bar
Bimetal
Thermal Overload Operation
Unlatch & Open
© 2001 Cooper Bussmann, Inc.
Spring Loaded ContactsLatch
Magnetic Element
Line
Load
Trip Bar Short Circuit Operation
Normal State
© 2001 Cooper Bussmann, Inc.
Spring Loaded ContactsUnlatch
Magnetic Element
Line
Load
Trip Bar Short Circuit Operation
Unlatching
© 2001 Cooper Bussmann, Inc.
Spring Loaded ContactsLatch
Magnetic Element
Line
Load
Trip Bar Short Circuit Operation
Opening
© 2001 Cooper Bussmann, Inc.
Spring Loaded ContactsLatch
Magnetic Element
Line
Load
Trip Bar Short Circuit Operation
Cleared
© 2001 Cooper Bussmann, Inc.
Coordination - Thermal-Mag Circuit BreakersCoordination - Thermal-Mag Circuit Breakers
Thermal Magnetic Molded Case Circuit Breaker Time-Current Curve Overload Region
Instantaneous RegionInterrupting TimeUnlatching Time
Interrupting RatingInterrupting Rating
© 2001 Cooper Bussmann, Inc.
Coordination - Thermal-Mag Circuit Breakers (See SPD)Coordination - Thermal-Mag Circuit Breakers (See SPD)
© 2001 Cooper Bussmann, Inc.
Selective Coordination
Current
Tim
e
A
B
C
D
4000A Fault
© 2001 Cooper Bussmann, Inc.
OPENS
NOT AFFECTED
UNNECESSARYPOWER LOSS Fault
Lacking Coordination
© 2001 Cooper Bussmann, Inc.
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
© 2001 Cooper Bussmann, Inc.
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)
© 2001 Cooper Bussmann, Inc.
Selective Coordination - LV Air Power Circuit Breakers (See SPD)Selective Coordination - LV Air Power Circuit Breakers (See SPD)
Short Time Delay - Allows the fault current to flow for up to 30 cycles.
Used to coordinate with downstream
Subjects equipment to high mechanical and thermal stresses, often violating 110.10
Arc Flash/ Blast Risks Much Higher
High Cost, Larger Equipment
© 2001 Cooper Bussmann, Inc.
Selective Coordination: Fuses
© 2001 Cooper Bussmann, Inc.
© 2001 Cooper Bussmann, Inc.
Time Current Curves
Selective Coordination:Fuses (See SPD)
© 2001 Cooper Bussmann, Inc.
Selectivity Ratio
Guide Based on
Thermal Principle
Based on I2t Clear Clear
Not MeltNot Melt
I2t melting > I2t Clearing 1200 A 600 A
Selective Coordination:Fuses (See SPD)
© 2001 Cooper Bussmann, Inc.
Selective Coordination (See SPD )
Selectivity Ratio Table Assures Coordination!No Plotting required!
LOW-PEAK® : LOW-PEAK®
2:1 Line:Load Ratio
Lin
e S
ide
Fu
se
Load Side Fuse
© 2001 Cooper Bussmann, Inc.
Example:
Main: KRP-C 1200 SP
Feeder: LPS-RK 200 SP
Branch: LPS-RK-30 SP
MSB
1200 A
200 A
30 A
480V, 3 phase
MCC
GFP
Selective Coordination - Fuses
© 2001 Cooper Bussmann, Inc.
Selective Coordination - Fuses
Use Selectivity Table
Main KRP-C 1200 SP
Feeder LPS-RK 200 SP
Branch LPS-RK 30 SP
What happens: Branch Circuit Isca = 5000 A or 50,000A or 300,000A ?
© 2001 Cooper Bussmann, Inc.
Lineside KRP-C 1200SP to Loadside LPS-RK 200SP
1200/200 = 6:1 Table only need 2:1 Selective Coordination
Lineside LPS-RK 200SP to Loadside LPS-RK 30SP
200/30= 6.67:1 Table only need 2:1
Selective Coordination
Selective Coordination- Fuses
© 2001 Cooper Bussmann, Inc.
Fault
NOT AFFECTED
OPENS
Selective Coordination
© 2001 Cooper Bussmann, Inc.
Selective Coordination
Simple Rules for Checking
• Circuit Breakers (instantaneous trip)
• Fuses
Can you look at this Can you look at this and assess whether and assess whether coordinated?coordinated?
You do not even You do not even need to draw curve!need to draw curve!
Simple Rule:Simple Rule:(Amp rating) x (I.T. setting) =(Amp rating) x (I.T. setting) = Isca @ which CB will unlatch:Isca @ which CB will unlatch:
CB IT ITCB IT IT Amp Amp Set Set Amp PickupAmp Pickup 100 5X100 5X 500 500 200 5X200 5X 1,000 1,000 400 10X 4,000400 10X 4,0001600 12X1600 12X 19,00019,000
See SPD See SPD
100 A100 A200 A200 A
400 A400 A
1600 A1600 A
© 2001 Cooper Bussmann, Inc.
Selective Coordination
• You already know the simple rule for fuses.
• Simply use amp rating ratios
• Typically 2:1 for
Low Peak Fuses to Low Peak Fuses
© 2001 Cooper Bussmann, Inc.
Selective Coordination
• Do coordination exercise using simple rules– Fusible system
– Circuit breaker system
• It’s simple!
© 2001 Cooper Bussmann, Inc.
Fault 10000 Amps
Low PeakKRP-C 1000 SP
Low PeakLPJ 200 SP
Low PeakLPJ 20 SP
Are These Selectively Coordinated?
© 2001 Cooper Bussmann, Inc.
Fault 10000 Amps
Low PeakKRP-C 1000 SP
Low PeakLPJ 200 SP
Low PeakLPJ 20 SP
Are These Selectively Coordinated?
OPENS
NOT AFFECTED
Fault 10000 Amps
Low PeakKRP-C 1000 SP
Low PeakLPJ 200 SP
Low PeakLPJ 20 SP
Selectively Coordinated
© 2001 Cooper Bussmann, Inc.
Are These Selectively Coordinated?
Fault 10000 Amps
1000 A. CBIT @ 10 X
200 A. CBIT @ 10 X
20 A. CBIT @ 10X
© 2001 Cooper Bussmann, Inc.
Are These Selectively Coordinated?
Fault 10000 Amps
1000 A. CBIT @ 10 X
200 A. CBIT @ 10 X
20 A. CBIT @ 10X
Not Coordinated
OPENS
NOT AFFECTED
Fault 10000 Amps
1000 A. CBIT @ 10 X
200 A. CBIT @ 10 X
20 A. CBIT @ 10X
© 2001 Cooper Bussmann, Inc.
UnnecessaryBlackout
The Issue:Lack of coordinationtakes out other loads
OPENSFault 10000 Amps
1000 A. CBIT @ 10 X
200 A. CBIT @ 10 X
20 A. CBIT @ 10X
© 2001 Cooper Bussmann, Inc.
Ground Fault Protection 230-95
© 2001 Cooper Bussmann, Inc.
See SPDSee SPD
© 2001 Cooper Bussmann, Inc.
GFP Health Care 517-17
Where one level of GFP is provided per 230.95 or 215.10 an additional step of GFP on feeders required.
The Ground Fault Protection for service and feeder shall be fully Selectively Coordinated
What does this mean ?
© 2001 Cooper Bussmann, Inc.
517-17 Health Care GFP
Main 1200 A CB
Feeder 200 A CB
GFP on Main & Feeder
Does this meet 517-17?
© 2001 Cooper Bussmann, Inc.
517-17 Health Care GFP
Main 1200 A Fuse
Feeder 200 A Fuse
GFP on Main & Feeder
Does this meet 517-17?
© 2001 Cooper Bussmann, Inc.
Following Excerpts from IEEE Standards
© 2001 Cooper Bussmann, Inc.
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.
© 2001 Cooper Bussmann, Inc.
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.
© 2001 Cooper Bussmann, Inc.
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.
© 2001 Cooper Bussmann, Inc.
IEEE 242-1986 “BUFF BOOK”Protection and Coordination of Industrial and Commercial Power Systems
Page 528 Coordination 14.1 A coordination study should be made when the available short-circuit current of the source to the plant is increased.
© 2001 Cooper Bussmann, Inc.
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.
© 2001 Cooper Bussmann, Inc.
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.
© 2001 Cooper Bussmann, Inc.
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,
© 2001 Cooper Bussmann, Inc.
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.
© 2001 Cooper Bussmann, Inc.
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.
© 2001 Cooper Bussmann, Inc.
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.
© 2001 Cooper Bussmann, Inc.
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.
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