Selective Coordination

1. Selective Coordination In-Depth Presentation of Short Circuit Selective Coordination with Low-Voltage Circuit Breakers IEEE IAS San Francisco and Santa Clara Chapter Ed Larsen, Senior Member Industry Standards Manager Square D/Schneider Electric

2. Introduction Definition NEC Selective Coordination Requirements The Challenge Circuit Breaker Principles Resources from the Manufacturers Challenges Meeting the NEC Design Guidelines Example Summary SF IAS Sel Coord.ppt 2

3. Definition NEC Selective Coordination Requirements The Challenge Circuit Breaker Principles Resources from the Manufacturers Challenges Meeting the NEC Design Guidelines Example Summary SF IAS Sel Coord.ppt 3

4. Definition: What is selective coordination? NEC Article 100 defines selective coordination as… Coordination (Selective). Localization of an overcurrent condition to restrict outages to the circuit or equipment affected, accomplished by the choice of overcurrent protective devices and their ratings or settings. In other words… Only the overcurrent protective device (OCPD) nearest to a fault should clear the fault SF IAS Sel Coord.ppt 4

6. NEC Selective Coordination Requirements Article 240 Overcurrent Protection 240.12 Electrical System Coordination. Where an orderly shutdown is required to minimize the hazard(s) to personnel and equipment, a system of coordination based on the following two conditions shall be permitted: (1) Coordinated short-circuit protection (2) Overload indication based on monitoring systems or devices FPN: The monitoring system may cause the condition to go to alarm, allowing corrective action or an orderly shutdown, thereby minimizing personnel hazard and equipment damage. Unchanged SF IAS Sel Coord.ppt 6

7. NEC Selective Coordination Requirements Article 517 Health Care Facilities 517.17 Ground-Fault Protection. (C) Selectivity. Ground-fault protection for operation of the service and feeder disconnecting means shall be fully selective such that the feeder device, but not the service device, shall open on ground faults on the load side of the feeder device. A six-cycle minimum separation between the service and feeder ground-fault tripping bands shall be provided. Operating time of the disconnecting devices shall be considered in selecting the time spread between these two bands to achieve 100 percent selectivity. FPN: See 230.95, fine print note, for transfer of alternate source where ground-fault protection is applied. Unchanged SF IAS Sel Coord.ppt 7

8. NEC Selective Coordination Requirements Article 620 Elevators, Dumbwaiters, Escalators, Moving Sidewalks, Wheelchair Lifts, and Stairway Lift Chairs 620.62 Selective Coordination. Where more than one driving machine disconnecting means is supplied by a single feeder, the overcurrent protective devices in each disconnecting means shall be selectively coordinated with any other supply side overcurrent protective devices. Unchanged SF IAS Sel Coord.ppt 8

9. 2005 NEC Selective Coordination Requirements Article 700 Emergency Systems 700.27 Coordination. Emergency system(s) overcurrent devices shall be selectively coordinated with all supply side overcurrent protective devices. 701.18 Coordination. Legally required standby system(s) overcurrent devices shall be selectively coordinated with all supply side overcurrent protective devices. New New SF IAS Sel Coord.ppt 9

10. 2005 NEC Selective Coordination Requirements Article 517 Health Care Facilities 517.26 Application of Other Articles. The essential electrical system shall meet the requirements of Article 700, except as amended by Article 517. New SF IAS Sel Coord.ppt 10

11. Typical Health-Care Facility Electrical System (2005 NEC FPN Figure 517.30) SF IAS Sel Coord.ppt 11

12. 2008 NEC Selective Coordination Requirements Article 700 Emergency Systems II. Circuit Wiring 700.9 Wiring, Emergency System. (B) Wiring. Exception to (5)(b): Overcurrent protection shall be permitted at the source or for the equipment, provided the overcurrent protection is selectively coordinated with the downstream overcurrent protection. New SF IAS Sel Coord.ppt 12

13. 2008 NEC Selective Coordination Requirements Articles 700 Emergency Systems and 701 Legally Required Standby Systems The following exception was added to sections 700.27 and 701.18 Exception: Selective coordination shall not required in the following circuits: (1) Between transformer primary and secondary overcurrent protective devices, where only one overcurrent protective device or set of overcurrent protective devices exist(s) on the transformer secondary, or (2) Between overcurrent protective devices of the same size (ampere rating) in series. New SF IAS Sel Coord.ppt 13

14. 2008 NEC Selective Coordination Requirements SECONDARY CB PRIMARY CB LV TRANSFORMER Making these two breakers coordinate with one another does not enhance system selectivity! SF IAS Sel Coord.ppt 14

15. 2008 NEC Selective Coordination Requirements PANEL 1 PANEL 2 CB 1 CB 2 G CB 1 CB 1 ENGINE-GENERATOR SET SWITCHBOARD Making these breakers coordinate with one another does not enhance system selectivity! SF IAS Sel Coord.ppt 15

16. 2008 NEC Selective Coordination Requirements Article 708 Critical Operations Power Systems 708.1 Scope. The provisions of this article apply to the installation, operation, monitoring, control, and maintenance of the portions of the premises wiring system intended to supply, distribute and control electricity to designated critical operations areas (DCOA) in the event of disruption to elements of the normal system. Critical operations power systems are those systems so classed by municipal, state, federal, or other codes, by any governmental agency having jurisdiction, or by facility engineering documentation establishing the necessity for such a system. These systems include but are not limited to power systems. HVAC. fire alarm. security. communications and signaling for designated critical operations areas. Note: This NEC article was renumbered from 585 to 708 New SF IAS Sel Coord.ppt 16

17. 2008 NEC Selective Coordination Requirements SF IAS Sel Coord.ppt 17 Article 708 Critical Operations Power Systems 708.1 Scope. FPN No. 1: Critical Operations Power Systems are generally installed in vital infrastructure facilities that, if destroyed or incapacitated, would disrupt national security, the economy, public health or safety; and where enhanced electrical infrastructure for continuity of operation has been deemed necessary by governmental authority. New •Air traffic control centers •Central station service facilities (fire and security system monitoring) •Chemical, petrochemical, and hazardous material (including biohazard) handling facilities •Communications centers, telephone exchanges, cellular tower sites •Emergency evacuation centers •Financial, banking, business data processing facilities Note: This list was in an early draft of the article but is not be in the final text •Fuel supply pumping stations (i.e. natural gas distribution and delivery infrastructure) •Hospitals and associated support facilities •Municipal infrastructure – water and sewer treatment facilities •911 centers •Offices and facilities deemed critical to continuity of government •Police, fire, civil defense facilities including power for radio repeater operations •Radio and television stations •Transportation infrastructure – airports, rail stations, seaports

18. 2008 NEC Selective Coordination Requirements Article 708 Critical Operations Power Systems 708.54 Coordination. Critical operations power system(s) overcurrent devices shall be selectively coordinated with all supply side overcurrent protective devices. Note: No exceptions! New SF IAS Sel Coord.ppt 18

20. Selectivity is typically achieved with circuit breakers by coordinating the time-current curve (TCC) characteristics of the devices to be coordinated Coordinated in the overload zone Seemingly not coordinated in the short circuit zone Can circuit breakers comply with the Code? 10 10 100100 1K1K 10K10K 100K100K 0.01 0.01 0.10 0.10 1 1 10 10 100 100 1000 1000 CURRENT IN AMPERES TIMEINSECONDS CB M1 CB F1 CB PM1 CB B1 CB M1 CB F1 CB PM1 CB B1 The Challenge SF IAS Sel Coord.ppt 20

22. Circuit Breaker Principles How the Instantaneous Trip Function Works T-M Breakers – Fixed instantaneous – Factory set – Must hold/trip values in the Digest reflect the TCC tolerance – Adjustable instantaneous – Factory set low – Final adjustment subject to +30%/-20% tolerance per UL 489 SF IAS Sel Coord.ppt 22

23. Circuit Breaker Principles How the Instantaneous Trip Function Works Electronic Trip Breakers – Adjustable instantaneous – Factory set low – Final adjustment subject to +/-10% tolerance – Selective override – Factory set for breaker self-protection – Usually +/-10% tolerance – Making current release (discriminator)* – Factory set for breaker self-protection – +/-10% tolerance – Turned off by a timer or switch after mechanism is latched* Typically LVPCBs only SF IAS Sel Coord.ppt 23

24. Circuit Breaker Principles Selective Override 5. For a withstand circuit breaker, instantaneous can be turned OFF. See 613-7 for instantaneous trip curve. See 613-10 for instantaneous override values. 10 10 100100 1K1K 10K10K 100K100K 0.01 0.01 0.10 0.10 1 1 10 10 100 100 1000 1000 CURRENT IN AMPERES TIMEINSECONDS Current Scale X 10^0 Reference Voltage: 480 TCC view SF IAS Sel Coord.ppt 24

25. Circuit Breaker Principles Making Current Release SF IAS Sel Coord.ppt 25 The MCR results in a close and latch rating

26. Circuit Breaker Principles Factors Impacting Short Circuit Selective Coordination Using time-current curves alone sometimes leads to the determination of a short circuit selective coordination level that is lower than can actually be achieved. Factors to consider… How Time-Current Curves are Developed Current Limiting Properties of Circuit Breakers Dynamic Characteristics of Circuit Breakers SF IAS Sel Coord.ppt 26

27. Circuit Breaker Principles Selective Coordination with 2 Circuit Breakers in Series – Time-Current Curves (TCCs) vs. Tested Levels TCCs – Developed by testing a circuit breaker by itself – In the short circuit region may not be valid for two circuit breakers connected in series Tested Levels – Take into account the current limiting properties and dynamic impedance of circuit breakers – Developed by comparing the actual let-through current of the downstream circuit breaker with minimum instantaneous trip of the upstream circuit breaker – Same principle as fuse ratio tables 10 10 100100 1K1K 10K10K 100K100K 0.01 0.01 0.10 0.10 1 1 10 10 100 100 1000 1000 CURRENT IN AMPERES TIMEINSECONDS SF IAS Sel Coord.ppt 27

28. Circuit Breaker Principles What is Needed for Good Selectivity Withstand Capability – Ability to withstand a high level of current – Dependent on many factors, such as... – Current path geometry – Contact pressure springs – Mechanism Trip System – Ability to utilize the withstand capability of the breaker – Dependent on many factors, such as... – Accuracy of the sensors – Adjustments available to the user Upstream breakers must have both for the best selective coordination! SF IAS Sel Coord.ppt 28

30. Resources from the Manufacturers Short Circuit Selective Coordination Tables Present short circuit selective coordination data for various tested combinations of low-voltage circuit breakers May yield higher levels of short circuit selective coordination than the TCCs indicate TCC studies still have to be made in order address overload and other protection issues SF IAS Sel Coord.ppt 30

31. Resources from the Manufacturers Short Circuit Selective Coordination Tables Eaton – Selective Coordination Industry Application (IA01200002E) – Selective Coordination Breaker Application Chart For Molded Case Circuit Breakers fed by Distribution Transformers General Electric – GE Overcurrent Device Instantaneous Selectivity Tables (DET-537) Siemens – Selective Trip Coordination with Molded Case Circuit Breakers – Selective Trip Coordination with Molded Case Circuit Breakers SF IAS Sel Coord.ppt 31

32. Resources from the Manufacturers Short Circuit Selective Coordination Tables Square D – Short Circuit Selective Coordination for Low Voltage Circuit Breakers (0100DB0501) – Selectivity Guidelines for Square D Panelboards (0100DB0604) – Enhancing Short Circuit Selective Coordination with Low Voltage Circuit Breakers (011DB0403) SF IAS Sel Coord.ppt 32

33. Design and Application Guides Eaton – Selective Coordination Square D – Guide to Overcurrent Coordination 600V and Below (0100DB0603) Resources from the Manufacturers SF IAS Sel Coord.ppt 33

34. Other Resources General Electric – InstaPlan™ 2.0, a tool for planning power system instantaneous selective coordination Eaton – 2005 NEC Selective Coordination Design Issues – Selective Coordination Calculator Resources from the Manufacturers SF IAS Sel Coord.ppt 34

35. Resources from the Manufacturers Square D Assumptions Circuit Breaker Contact Position All upstream breakers are in the closed (ON) position when the fault occurs Instantaneous Trip Setting The instantaneous trip setting on all upstream breakers, if adjustable, will be set to the highest position (OFF if available – select LSI or LSIG trip units) SF IAS Sel Coord.ppt 35

36. Using Short Circuit Selective Coordination for Low Voltage Circuit Breakers (0100DB0501) SF IAS Sel Coord.ppt 36

37. Basic Information Needed System One-line Diagram System Voltage Circuit Ampacity Available Short Circuit Current Add motor contribution (if necessary) Adjust for X/R (if necessary) From the normal source to the lowest point in the system From the alternate source to the first bus below the ATS SF IAS Sel Coord.ppt 37

38. Available Short Circuit Current SF IAS Sel Coord.ppt 38 G CB 1 G CB 2 AUTOXFER SW CB 4 TO NORMAL SOURCE E N CB 3 AUTOXFER SW E N AUTOXFER SW CB 5 E N CB 6 Normal source SCA Alternate source SCA This assumes the alternate source SCA < the normal source SCA

39. Example #1 - System Description System 208Y/120 Vac system with 10 kSCA available at the lighting panelboard Equipment NQOD 225A main lugs lighting panelboard with single pole 20A QOB 10 kAIR rated circuit breakers fed from a QDA32225 circuit breaker with a 25 kA interrupting rating located in an upstream I-Line power panelboard SF IAS Sel Coord.ppt 39

40. Example #1 - Determining the Level of Short Circuit Selective Coordination 1. Find the 240Vac table listing QO downstream circuit breakers in Appendix A Table 1 on page 6 2. Find the column for the QO downstream circuit breaker to be studied 3. Go down the column until the row listing the 225 A QD upstream circuit breaker is found 4. Read the selective coordination level at the intersection of the column and row, namely 2.0 kA. This means that the QD upstream circuit breaker is selectively coordinated with downstream QO circuit breakers up to 2,000 amps. SF IAS Sel Coord.ppt 40

41. Example #1 - Improving the Level of Short Circuit Selective Coordination Using the same example, determine if a higher level of selective coordination can be achieved by following these steps: 1. Move down the column for the QO downstream circuit breaker to be studied, looking for upstream breakers that will yield a higher level of selective coordination 2. When the desired level of selective coordination is found, read across the row to find the upstream breaker that will yield this level. In this case, an LA-MC circuit breaker will yield a level of selective coordination of up to 18,000 amps. Footnote 10 refers to Appendix B. SF IAS Sel Coord.ppt 41

42. Example #1 - Improving the Level of Short Circuit Selective Coordination Referring to Appendix B Table 12 on page 38 1. Find the column for the QO downstream circuit breaker to be studied 2. Go down the column until the row listing the 225 A LA-MC upstream circuit breaker is found 3. Read the selective coordination level at the intersection of the column and row, namely 18 kA for a series rated application 4. Footnote 2 indicates that for a fully rated application the level of selective coordination is 10 kA. This means that the LA-MC upstream circuit breaker is fully selectively coordinated with downstream QO circuit breakers up to 10,000 amps SF IAS Sel Coord.ppt 42

43. SF IAS Sel Coord.ppt 43 Example #1 - Improving the Level of Short Circuit Selective Coordination                                                     Name: PD-0001 Manufacturer: *SQUARE D Type: LA, LH/MC Frame/Model: 250A Trip: 225 A Voltage: 240 V Settings: Phase Fixed Name: PD-0006 Manufacturer: *SQUARED Type: QO, 1P Frame/Model: 20A Trip: 20 A Voltage: 240 V Settings: Phase Fixed (730-3) Name: PD-0001 Manufacturer: *SQUARE D Type: LA, LH/MC Frame/Model: 250A Trip: 225 A Voltage: 240 V Settings: Phase Fixed Name: PD-0006 Manufacturer: *SQUARED Type: QO, 1P Frame/Model: 20A Trip: 20 A Voltage: 240 V Settings: Phase Fixed (730-3) Coordinates to 18kA per Data Bulletin 0100DB0501 Coordinates to 18kA per Data Bulletin 0100DB0501 Current Scale x 1 Reference Voltage: 240 There is an overlap on the TCC However, these two circuit breakers coordinate to 10 kA, the level of short- circuit current at the downstream circuit breaker They are fully coordinated A text note is used to delineate that this breaker combination coordinates above the level shown on the TCC

44. Example #2 - System Description System 480Y/277 Vac system with 25 kSCA available at the lighting panelboard Equipment NF 250A main lugs lighting panelboard with single pole EG 35 kAIR rated circuit breakers fed from a JGA36250 circuit breaker with a 35 kA interrupting rating located in an I-Line power panelboard SF IAS Sel Coord.ppt 44

45. Example #2 - Determining the Level of Short Circuit Selective Coordination 1. Find the 480Vac table listing EG downstream circuit breakers in Appendix A, Table 6: on page 20 2. Find the column for the EG downstream circuit breaker to be studied 3. Go down the column until the row listing the 250 A JG upstream circuit breaker is found 4. Read the selective coordination level at the intersection of the column and row, namely 2.4 kA. This means that the JG upstream circuit breaker is selectively coordinated with downstream EG circuit breakers up to 2,400 amps. SF IAS Sel Coord.ppt 45

46. Example #2 - Improving the Level of Short Circuit Selective Coordination Using the same example, determine if a higher level of selective coordination can be achieved by following these steps: 1. Move down the column for the EG downstream circuit breaker to be studied, looking for upstream breakers that will yield a higher level of selective coordination 2. When the desired level of selective coordination is found, read across the row to find the upstream breaker that will yield this level. In this case, a PG circuit breaker will yield a level of selective coordination of 35,000 amps. This means that the upstream PG circuit breaker is fully selective with downstream EG circuit breakers. SF IAS Sel Coord.ppt 46

47. SF IAS Sel Coord.ppt 47 Example #2 - Improving the Level of Short Circuit Selective Coordination                                                     Name: PD-0006 Manufacturer: *SQUARE D Type: EG Frame/Model: 20A Trip: 20 A Voltage: 480 V Settings: Phase Fixed Name: PD-0001 Manufacturer: SQUARED Type: POWERPACT P-Frame, 3.0 & 3.0A Frame/Model: PG Trip: 250 A Voltage: 480 V Settings: Phase LTPU/LTD (A 0.4-1.0 x S) 1 (250A); 0.5 INST PG 250-1200 (1.5-12 X S) 6 (1500A) Name: PD-0006 Manufacturer: *SQUARE D Type: EG Frame/Model: 20A Trip: 20 A Voltage: 480 V Settings: Phase Fixed Name: PD-0001 Manufacturer: SQUARED Type: POWERPACT P-Frame, 3.0 & 3.0A Frame/Model: PG Trip: 250 A Voltage: 480 V Settings: Phase LTPU/LTD (A 0.4-1.0 x S) 1 (250A); 0.5 INST PG 250-1200 (1.5-12 X S) 6 (1500A) Coordinates to 35ka per Data Bulletin 0100DB0501 Coordinates to 35ka per Data Bulletin 0100DB0501 Current Scale x 1 Reference Voltage: 480 There is an overlap on the TCC However, these two circuit breakers coordinate to 35 kA, above the level of short-circuit current at the downstream circuit breaker They are fully coordinated A text note is used to delineate that this breaker combination coordinates above the level shown on the TCC

48. Using Enhancing Short Circuit Selective Coordination with Low Voltage Circuit Breakers (011DB0403) SF IAS Sel Coord.ppt 48

49. Using Enhancing Short Circuit Selective Coordination How to Use Appendix A Find the table with the correct system voltage Find the breaker to be studied Find the maximum instantaneous or selective override trip level Suggestion Use this data bulletin when the desired combination cannot be found in Short Circuit Selective Coordination for Low Voltage Circuit Breakers SF IAS Sel Coord.ppt 49

50. Using Enhancing Short Circuit Selective Coordination Example – Coordination Across a LV Transformer To select a primary circuit breaker that will coordinate with secondary branch circuit breakers: 1. Determine the available SCA downstream (assume 1 kA) 2. Calculate the fault current that will be seen on the primary: 208 V / 480 V = 0.433 x 1000 A = 433 A 3. Find a circuit breaker with the proper voltage, interrupting and continuous current ratings in Appendix A that also has an instantaneous trip of at least 433 A 4. Check to make sure that the primary circuit breaker meets the NEC transformer protection requirements Enhancing Short Circuit Selective Coordination does not present new information, it just compiles it in one easy to use location! SF IAS Sel Coord.ppt 50

51. Definition 2005 NEC Selective Coordination Requirements The Challenge Circuit Breaker Principles Resources from the Manufacturers Challenges Meeting the NEC Design Guidelines Example Summary SF IAS Sel Coord.ppt 51

52. Challenges Meeting the NEC What to do? Understand the issues with the NEC requirements Know the AHJ’s interpretation of NEC 700.27 and 701.18 Know how NEC 700.27 and 701.18 is enforced in your area (or if it will be enforced, state or local exceptions, etc.) – Will selective coordination be required up to both the normal and alternate sources, or only up to the alternate source? – What about existing equipment (such as an old switchboard feeding a new panelboard)? SF IAS Sel Coord.ppt 52

53. Challenges Meeting the NEC Is selective coordination required up to both the normal and alternate sources, or only up to the alternate source? 700.1 Scope. The provisions of this article apply to…emergency systems…intended to supply, distribute, and control electricity…when the normal electrical supply or system is interrupted… These systems are intended to automatically supply illumination, power, or both…in the event of failure of the normal supply... The scope seems to imply only up to the alternate source SF IAS Sel Coord.ppt 53

54. Challenges Meeting the NEC Is selective coordination required up to both the normal and alternate sources, or only up to the alternate source? Appendix B.1 of NFPA 110 also seems to imply only up to the alternate source SF IAS Sel Coord.ppt 54

55. Challenges Meeting the NEC Is selective coordination required up to both the normal and alternate sources, or only up to the alternate source? But read 700.27 carefully 700.27 Coordination. Emergency system(s) overcurrent devices shall be selectively coordinated with all supply side overcurrent protective devices. Normal system OCPDs are on the supply side of the emergency system, and thus are included (Square D interpretation) SF IAS Sel Coord.ppt 55

56. Challenges Meeting the NEC Examples of Code Modifications State of Washington – 027 Coordination. The requirements for selective coordination described in NEC 700.27 are not required where the emergency system was installed prior to June 1, 2006. For new emergency systems that are supplied from an existing emergency system installed prior to June 1, 2006, the new portion of the emergency system must comply with NEC 700.27. The ground fault sensing function of overcurrent protective devices will only be required to selectively coordinate with the ground fault sensing functions of other overcurrent protective devices. – A similar modification was made to 701.18 SF IAS Sel Coord.ppt 56

57. Challenges Meeting the NEC Examples of Code Modifications State of Massachusetts 2008 MEC Added the following to 700.27 and 701.18 Exception No. 2: Where the emergency system design is under the control of a licensed professional engineer engaged in the design or maintenance of electrical installations, the selection of overcurrent protective devices shall be permitted to coordinate to the extent practicable. The design shall be documented, stamped by the professional engineer, and made available for review by the authority having jurisdiction. FPN: Overcurrent protective devices used for emergency circuit protection, where coordinated to optimize selective operation of the circuit overcurrent protective devices when a short circuit or ground fault occurs, increase overall reliability of the system. SF IAS Sel Coord.ppt 57

58. Challenges Meeting the NEC Examples of Code Modifications City of Tucson – Section 700.27 Coordination. DELETE this section in its entirety. – Section 701.18 Coordination. DELETE this section in its entirety. State of Florida – Healthcare facilities come under the jurisdiction of AHCA for plan check and inspection – Requires selective coordination to 0.1 sec. SF IAS Sel Coord.ppt 58

59. Challenges Meeting the NEC Examples of Code Modifications State of California – Healthcare facilities come under the jurisdiction of OSHPD for plan check and inspection – Proposals – 700.27 Coordination. Emergency system(s) overcurrent devices shall be selectively coordinated with all supply side overcurrent protective devices. [Not permitted for OSHPD 1, 2, 3, & 4] – 701.18 Coordination. Legally required standby system(s) overcurrent devices shall be selectively coordinated with all supply side overcurrent protective devices. [Not permitted for OSHPD 1, 2, 3, & 4] SF IAS Sel Coord.ppt 59

60. Challenges Meeting the NEC Examples of Code Modifications State of Wisconsin – Proposals – 517.26 Application of Other Articles. The essential electrical system shall meet the requirements of Article 700, except as amended by Article 517. Essential electrical system(s) overcurrent devices shall be selectively coordinated with all supply side overcurrent protective devices for faults with a duration of 0.1 seconds and longer. The selection and coordination of the overcurrent devices shall be documented and stamped by a professional engineer and approved by the engineer of record for the project. This study and all associated documentation shall be made available for review by the authority having jurisdiction. SF IAS Sel Coord.ppt 60

61. Challenges Meeting the NEC Examples of Code Modifications State of Wisconsin – Proposals – 700.27 Coordination. – Emergency system(s) overcurrent devices shall be selectively coordinated with all supply side overcurrent protective devices for faults with a duration of 0.1 seconds and longer. – 701.18 Coordination. – Legally required standby system(s) overcurrent devices shall be selectively coordinated with all supply side overcurrent protective devices for faults with a duration of 0.1 seconds and longer. – 708.54 Coordination. – Critical operations power system(s) overcurrent devices shall be selectively coordinated with all supply side overcurrent protective devices for faults with a duration of 0.1 seconds and longer. – Exceptions: – (1) Between transformer primary and secondary overcurrent protective devices, where only one overcurrent protective device or set of overcurrent protective devices exists on the transformer secondary, – (2) Between overcurrent protective devices of the same size (ampere rating) in series. SF IAS Sel Coord.ppt 61

62. Challenges Meeting the NEC Examples of Code Modifications New York City – Question (from a consulting engineer dated 9/26/07) “The NEC sections 700.27 and 701.18 require that ‘Emergency System(s) overcurrent devices shall be selectively coordinated with all supply side overcurrent protective devices.’ Does this mean that all the emergency system overcurrent devices, from the smallest branch to the power supply, must be selectively coordinated?” – Answer (from the NYC Electrical Code Revision and Interpretation Committee dated 9/15/07) “Selective coordination requirements for short-circuit conditions are defined in section 240.12. Emergency system(s) overcurrent devices, per section 700.27, shall be selectively coordinated for overcurrent conditions only.” SF IAS Sel Coord.ppt 62

63. Challenges Meeting the NEC Examples of Code Modifications New York City NYC Electrical Code (based on the 2005 NEC) Section 240.12 - Revise to read as follows: 240.12 Electrical System Coordination. Rating and arrangement of service overcurrent devices, which have a rating above 601 amperes, shall be selectively coordinated. Such coordination shall provide a system of selective short circuit and overload protection between the service overcurrent protection and the second level overcurrent protection point. Where an orderly shutdown is required to minimize the hazard(s) to personnel and equipment, an additional overcurrent protection level is permitted. A system of coordination based on the following two conditions shall be permitted: (1) Coordinated short-circuit protection (2) Overload indication based on monitoring systems or devices. SF IAS Sel Coord.ppt 63

64. Challenges Meeting the NEC Examples of Code Modifications New York City New York City Electrical Code (based on the 2005 NEC) Section 240.12 - Revise to read as follows: 240.12 Electrical System Coordination. Exception No. 1: Service overcurrent devices which supply single loads (i.e., motors) shall not require coordination. Exception No. 2: Coordination between the service overcurrent device and distribution main shall not be required where the service disconnecting means supplies a single main overcurrent device for a single distribution panel or switchboard. However, selective coordination shall be required between distribution branch devices, and between the service equipment and the main panel. Exception No. 3: The provisions of this Section shall not apply to the operation of ground fault protection equipment. SF IAS Sel Coord.ppt 64

65. Challenges Meeting the NEC Examples of Enforcement State of Washington – Selective coordination must be assured by a state licensed PE – The Department of Labor and Industries is interpreting the Code to mean that selective coordination is required only to the alternate source City of Tacoma – Selective coordination must be assured by a state licensed PE. A coordination study need not be submitted. (unconfirmed) City of Denver – Selective coordination required only to the alternate source (unconfirmed) SF IAS Sel Coord.ppt 65

66. Challenges Meeting the NEC Cautions Make sure automatic transfer switches have adequate withstand ratings – May need to relocate the switch, or – May need to increase the frame size of the switch Make sure busway has adequate withstand ratings Make sure the generator protection devices coordinate with the downstream circuit breakers Total ground fault selective coordination may not be possible, or may be difficult, due to other Code requirements [517.17(B)(1) and (2)] SF IAS Sel Coord.ppt 66

67. Challenges Meeting the NEC Cautions Mixing Overcurrent Protective Devices – Mixing OCPDs from different manufacturers or mixing fuses and circuit breakers requires using TCCs only – Fuse ratio or circuit breaker tables cannot be used Arc Flash – Selective coordination impact on arc flash PPE levels needs to be considered – May be possible to reduce with Zone Selective Interlocking SF IAS Sel Coord.ppt 67

69. Design Guidelines Conduct a Selective Coordination Study First Before letting a job out for bid, conduct a selective coordination study first as it may affect the system design Work from the Bottom Up Starting from the bottom of the system, coordinate the branch lighting panels first, then the power distribution panels, then the switchboard or switchgear SF IAS Sel Coord.ppt 69

70. Design Guidelines Nest Curves The time-current curve of a thermal- magnetic circuit breaker can sometimes be nested underneath the time-current curve of an upstream electronic trip circuit breaker Name: PD-0006 Manufacturer: *SQUARE D Type: EG Frame/Model: 20A Trip: 20 A Voltage: 480 V Settings: Phase Fixed Name: PD-0001 Manufacturer: SQUARED Type: POWERPACT P-Frame, 3.0 & 3.0A Frame/Model: PG Trip: 250 A Voltage: 480 V Settings: Phase LTPU/LTD (A 0.4-1.0 x S) 1 (250A); 0.5 INST PG 250-1200 (1.5-12 X S) 6 (1500A) Name: PD-0006 Manufacturer: *SQUARE D Type: EG Frame/Model: 20A Trip: 20 A Voltage: 480 V Settings: Phase Fixed Name: PD-0001 Manufacturer: SQUARED Type: POWERPACT P-Frame, 3.0 & 3.0A Frame/Model: PG Trip: 250 A Voltage: 480 V Settings: Phase LTPU/LTD (A 0.4-1.0 x S) 1 (250A); 0.5 INST PG 250-1200 (1.5-12 X S) 6 (1500A) SF IAS Sel Coord.ppt 70

71. Design Guidelines Use the Short Circuit Selective Coordination Tables Rather than the Time-Current Curves Feeding Lighting Panelboards Don’t feed lighting panelboards from lighting panelboards unless there is a transformer in between Other Lighting Panelboard Recommendations Better levels of selective coordination are available with 225A and larger panelboards Consider using main lugs panels SF IAS Sel Coord.ppt 71

72. Design Guidelines Increase the Frame Size of the Upstream Circuit Breaker The upstream circuit breaker should be at least one frame size larger than the downstream circuit breaker. This may necessitate increasing the size of panelboards and feeder conductors. Very high levels of short circuit selective coordination may be achieved by using high amp frame electronic trip circuit breakers with low amp sensors and/or lower ampere rating adjustments SF IAS Sel Coord.ppt 72

73. Design Guidelines SF IAS Sel Coord.ppt 73 Rarely needed, but as a last resort... Change the Upstream Circuit Breaker Type Insulated case circuit breakers or low voltage power circuit breakers Reduce the Voltage If the desired level of selective coordination cannot be achieved using a 480Y/277Vac panelboard, consider feeding a 208Y/120Vac panelboard through a transformer Split Up Some of the Loads (multiple smaller transformers) Insert Impedance Longer run of wire, 1:1 or higher impedance transformer or reactors

74. Design Guidelines Generator Protection Selective coordination is sometimes difficult or impossible while providing adequate generator protection Be wary of circuit breakers supplied with engine- generator sets – They are often thermal-magnetic or electronic trip with LI protection – They may need to be electronic trip with LS protection and high withstand if possible, or ANSI LV power circuit breakers Make sure generator protective relays or controls will coordinate with the downstream devices SF IAS Sel Coord.ppt 74

75. Design Guidelines Challenge: CB1 and CB2 must both be selective with CB3, CB4, CB5 and all downstream breakers (CB6…) G CB 1 G CB 2 AUTOXFER SW CB 4 TO NORMAL SOURCE E N CB 3 AUTOXFER SW E N AUTOXFER SW CB 5 E N CB 6 SF IAS Sel Coord.ppt 75

76. Design Guidelines One solution: More, smaller generators without paralleling G CB 1 G AUTOXFER SW TO NORMAL SOURCE E NAUTOXFER SW E N AUTOXFER SW E N CB 6 G Expensive! Decreases reliability Not always practical SF IAS Sel Coord.ppt 76

77. Design Guidelines Better solution: Allow paralleling switchgear feeders to provide short- circuit protection Supplement with bus-differential protection for the generator paralleling bus Not a “cure-all”, but it does often help SF IAS Sel Coord.ppt 77

78. G CB 1 G CB 2 AUTOXFER SW CB 4 TO NORMAL SOURCE E N CB 3 AUTOXFER SW E N AUTOXFER SW CB 5 E N CB 6 87B PROTECTIVE ZONE CB1 and CB2 set to provide overload, but not short-circuit, protection for the generators These settings allow coordination with CBs on the level of CB3 Bus differential protection provides short circuit protection for the generators for faults on generator paralleling bus CBs on CB3 level provide short circuit protection for generators Design Guidelines SF IAS Sel Coord.ppt 78

79. Design Guidelines Selective coordination requires an extremely high level of analysis Often not possible to achieve on conventional designs without major reconfiguration (cannot succeed with device selections alone) Expect significantly higher design time, space requirements, and equipment costs Vendor-Specific Design Difficult to delegate the design to a vendor by specifying “vendor shall provide fully selective equipment” because of effects on equipment sizes, room sizes, system layout strategy, feeder sizes, etc. Bogue Waller, P.E., Principal Electrical Engineer, Nash Lipsey Burch, LLC, Nashville, TN SF IAS Sel Coord.ppt 79

80. Design Guidelines Field Adjustment Don’t neglect to properly adjust circuit breakers in the field as they are often shipped from the factory with all but the ampere-rating switch in the lowest position SF IAS Sel Coord.ppt 80

81. Definition NEC Selective Coordination Requirements Circuit Breaker Principles Resources from the Manufacturers Design Guidelines Challenges Meeting the NEC Example Summary SF IAS Sel Coord.ppt 81

82. Example Which of these circuit breakers need to be selectively coordinated? SF IAS Sel Coord.ppt 82

83. Example Which of these circuit breakers need to be selectively coordinated? #3 must coordinate with #4 because it is a supply side device Yes SF IAS Sel Coord.ppt 83

84. Example Which of these circuit breakers need to be selectively coordinated? #1 does not need to coordinate with #3, assuming that they are both the same size, in accordance with Exception 2 in the 2008 NEC which states, "Exception: Selective coordination shall not be required in (1) or (2): (2) Between overcurrent protective devices of the same size (ampere rating) in series." #1 does need to coordinate with #4 and the other breakers on that bus. (Note: While this exception does not exist in the 2005 NEC, most engineers would come to this same conclusion, and most AHJs would probably agree.) No Yes SF IAS Sel Coord.ppt 84

85. Example Which of these circuit breakers need to be selectively coordinated? #A does not need to coordinate with #1 or 3, however, it does need to coordinate with #4 because it is a supply side device No Yes SF IAS Sel Coord.ppt 85

86. Example Which of these circuit breakers need to be selectively coordinated? #2 does not need to coordinate with #3, assuming that they are both the same size, but it does need to coordinate with #4 and the other breakers on that bus No YesYes SF IAS Sel Coord.ppt 86

87. Example Which of these circuit breakers need to be selectively coordinated? #A, #B and #C are not required to be coordinated in accordance with the scope of Article 700 and drawing B.1 in NFPA 110 Annex B This illustrates the problem with requiring coordination up to the normal source – if the normal loads are not coordinated, has the emergency system reliability really been improved? No No SF IAS Sel Coord.ppt 87

88. Definition NEC Selective Coordination Requirements Circuit Breaker Principles Resources from the Manufacturers Design Guidelines Challenges Meeting the NEC Example Summary SF IAS Sel Coord.ppt 88

89. Summary Understand the NEC Selective coordination requirements How the AHJ will interpret and enforce them Understand the Operating Characteristics of Circuit Breakers Limitations of the TCCs in the short circuit zone SF IAS Sel Coord.ppt 89

90. Summary Understand the Design Characteristics of Circuit Breakers Withstand Capability Instantaneous Trip Setting Field adjustable instantaneous adjustment can be turned OFF on LSI and LSIG trip units Continuous Current Rating Overlap Allows for selecting a larger frame size breaker, particularly on electronic trip circuit breakers SF IAS Sel Coord.ppt 90

91. Summary Evaluation Methodology Conduct a short circuit study (from both sources) Make initial circuit breaker selections Determine the selective coordination levels Optimizing Techniques Use the short circuit selective coordination tables rather than the TCCs if there is an overlap of the TCCs in the short circuit zone Consider better system configurations Increase the frame size of the upstream breakers Change the upstream breaker type Add impedance to reduce short circuit current levels SF IAS Sel Coord.ppt 91

92. Summary Low voltage circuit breaker based systems can be selectively coordinated! Thank You! Questions? SF IAS Sel Coord.ppt 92

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