selective coordination vs arc flash requirements

White Paper 0600DB130306/2013

Selective Coordination vs Arc Flash RequirementsRetain for future use.

2013 Schneider Electric All Rights Reserved

Abstract Present industry standards require higher system performance and protection against arc flash hazards for individuals exposed to dangerous levels of incidental energy. However, in most cases, high system performance achieved through selective coordination, required in changes to the National Electric Code (NEC), results in increased arc flash energy. This conflict between selective coordination and arc flash is explained in this paper through real world examples. The resolution to this conflict is provided through both existing and future solutions which achieve a balance between total selectivity and arc flash hazard levels. This paper also discusses the two levels of selective coordination commonly employed: 0.1 seconds and total selectivity; and the affects each has on calculated arc flash hazards.

Introduction

Selective Coordination Selective coordination refers to the selection and setting of overcurrent protective devices (OCPDs) in an electric power system in such a manner so as to cause the smallest possible portion of the system to be de-energized due to an overload condition:

Per the 2011 NEC Article 100 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.This ensures any overcurrent event is cleared by the smallest circuit breaker in the system before allowing a larger line-side circuit breaker to operate on the fault. This limits the service interruption to only the circuit experiencing the problem and does not shut down a larger portion of the facility.Specific selective coordination requirements were first introduced in NEC 1996, Article 620.62 for elevators, dumbwaiters, escalators, moving walks, wheelchair lifts and stairway chair lifts. Subsequent articles were added to the NEC: 1. Emergency and legally-required standby power systems, NEC 2011

Articles 700.27 and 701.27, respectively. 2. Health-care facilities, NEC Article 517.26, which says that the essential

electrical system should meet the requirements of Article 700.3. Critical operations power systems (COPS), NEC Article 708.54.While the rationale for selective coordination is self-evident clearing and isolating faults as quickly as possible without disturbing the unaffected portions of the system the methods for judging OCPD to OCPD selectivity are not as clear. No industry standards exist which define device-to-device selectivity over their full operating ranges; no consensus has been developed among protection engineers or inspecting authorities regarding device-to-device selectivity thresholds. Discussions continue over the practicable selectivity criteria overlaying time-current characteristics of OCPDs to determine selectivity are complicated by examining the current-limiting interactions of OCPDs at maximum available fault currents. As a

Selective Coordination vs Arc Flash Requirements 0600DB1303White Paper 06/2013

2 2013 Schneider Electric All Rights Reserved

result, essentially two interpretations or definitions of selective coordination have evolved:A. 0.1 seconds and longer This means that the time-current curves

(TCCs) of OCPDs in series should not overlap above 0.1s. Selective coordination at 0.1s and longer includes the vast majority of fault currents, overloads and arcing faults, but not the highest levels seen in the instantaneous region.

B. Total selectivity In addition to TCC coordination described for the 0.1s definition, total selectivity takes into account the current-limiting behaviors and interactions of OCPDs operating on the highest available fault currents. There are variations on how total selectivity is described (e.g. 0.01 seconds), but the intent is selectivity for the OCPDs entire operating range up to the maximum fault current.

Arc Flash The consideration of arc flash hazards is a relatively new concern for power system design. However, it is a concern that is rapidly gaining momentum due to increasingly strict worker safety standards. A flash hazard is a dangerous condition associated with the release of energy caused by an electric arc. The energy impressed on a surface, a certain distance from the source, generated during an electrical arc event is termed as incident energy. Key factors which affect the arc flash incident energy are:A. available fault current at the equipment B. the time taken by the upstream protective device to clear the fault C. distance from the arcing sourceIn most cases achieving selective coordination comes at the cost of increasing circuit breaker frame size and/or changing circuit breaker type from a molded case to an electronic trip type with higher short time/instantaneous settings. Both solutions could result in an increase in total clearing time of protective devices during an arcing fault, thereby causing an increase in arc flash incident energy. An example in the next section further explains the effect of selective coordination 0.1 second and total on arc flash.

Selective Coordination versus Arc Flash Example

Selective Coordination Through Comparison of Time-Current Curves

In this section a five bus circuit has been used to explain the affect of total selectivity on arc flash. Three cases have been considered as follows: Case 1 Load based coordination where devices are selected based on

typical thermal-magnetic trips for circuit breakers other than service mains and prior to implementing NEC Article 100 requirement of selective coordination.

Case 2 - Selective coordination to 0.1 seconds and longer Case 3 - Total selective coordinationTable 3 on Page 17 compares arc flash category and incident energy for each case. The results of this typical example show how selective coordination is achieved at the cost of increased arc flash incident energy. Figure 1 shows that the system is fed from two sources:A. normal source fed by a 1000 kVA utility transformer and B. emergency source fed by a 500 kW generator.

0600DB1303 Selective Coordination vs Arc Flash Requirements06/2013 White Paper


The protective devices shown are prior to selective coordination and are based on load requirement only.

Figure 1: Single Line Drawing of Example System

UTILITYSC Contribution 3P 99999 MVAX/R 3P 8.0

UTI XFM1000 kVAPrl 12470 VSec 480 VZ = 5.75%

GEN500 kW625 kVAPF 0.80 Lag

GM1PB800AF / AS / AT

50 ft.4#500

SM1PG1200AF / AS / AT

001 GEN480 V7.508 kA

AFELA400AT

005 SWBD480 V22.507 kAAFN

LA400AT

MTR LD500 hp500 kVAXd 0.25 PU

100 ft.1#500

E N

400A ATS

002L ATS480 V16.753 kA

003 PNL1480 V14.815 kAPB2

HG125AT

100 ft.1#500

50 ft.1#500

PB4EG40AT

50 ft.1#2

004 PNL2480 V11.857 kA



The cable length and sizes are noted on the one line drawing shown in Figure 1. The cables are sized per NEC 2011 Edition table 310.15(B) (16). In order to have a worst case fault analysis, the main switchboard was loaded with (20) 25 hp motors adding up to 500 kVA, half of the rated kVA of the utility transformer. The circuit breaker TCCs are plotted based on worst case three phase fault current from an infinite source. For this example it has been assumed that the entire system consisting of both normal and emergency sides should be selectively coordinated for each case:

a. Case 2: 0.1 second and longer and b. Case 3: total selectivity.

The TCC graphs shown in Figures 2 and 3 show coordination for Case 1: without more stringent selective coordination requirements. Without selectivity requirements the coordination achieved in Case 1 is borderline practicable; for fault level currents load-side of PB4, mis-coordination exists with line-side circuit breaker PB2, and mis-coordination exists for the highest levels of fault current for all of the circuit breakers plotted. However, when Case 2 and Case 3 are considered there are several issues, notably for Case 3. Selectivity will be achieved by adjusting the circuit breaker TCCs shown in Figures 2 and 3 and if required by replacing the circuit breakers with ones ensuring better coordination. Each case includes circuit breakers at equipment designations PNL1 and PNL2 fed from normal and emergency source.



Figure 2: Case 1 - TCC Graph for PNL2 Circuit Based on Normal Source Fault Current



In terms of selective coordination, Case 2 is considered first: selective coordination 0.1 seconds and longer. If Figures 2 and 3 are compared, both have a common OCPD mis-coordination issue which exists between circuit breakers PB2 and PB4. By replacing circuit breaker PB2 with a PowerPact circuit breaker HD 125AT trip 5.2A, we can improve selectivity to 0.1 seconds and longer. The circuit breakers AFN, AFE, SM1 and GM1 require setting adjustments in order to maintain selective coordination of 0.1 seconds and longer. The new TCC graphs are shown in Figures 4 and 5, for normal and emergency side, respectively. In order to achieve selective

Figure 3: Case 1 - TCC Graph for PNL2 Circuit Based on Emergency Source Fault Current



coordination for Case 2 there were few system design changes comprising of one circuit breaker upgrade and settings adjustment of existing circuit breakers.




For Case 3, the selectivity table and the online selectivity tool are used in order to improve coordination by removing the overlap in the instantaneous region between the circuit breaker curves as shown in Figures 2 and 3. The analysis starts at the smallest downstream circuit breaker in PNL2 and subsequently moves up the system to the main switchboard SWBD. There is an overlap in the instantaneous region of device PB4 with devices PB2, AFN and SM1.




Per Schneider Electric data bulletin 0100DB0501 [1] the circuit breakers HG 125AT [PB2] and EGB 40AT [PB4] are totally selective up to 1300 A. The available fault current at PNL2 is 11.857kA which is greater than 1300 A. Hence in case of a fault PB2 may trip along with PB4 resulting in lack of total selectivity for faults above 1300 A. In order to achieve total selectivity between circuit breakers PB2 and PB4 the following design options exist: A. Change the thermal magnetic circuit breaker PB2 to an electronic trip type

of same size with an adjustable short time and instantaneous setting. B. Increase the trip and frame size of circuit breaker PB2, thereby having a

higher instantaneous trip region. Note that the higher trip size would require an increase in cable size. Increased cable size will have lower impedance which in turn will increase the fault current at the panel PNL2.

C. Introduce an isolation transformer between ATS load side and PNL1. The isolation transformer will reduce the fault current.

D. Redesign the cable lengths to insure lower fault currents by increasing the cable length and impedance. This is a worst case option when total selectivity is required and there are no circuit breaker pairs available. Drawbacks of D are that the building may not be conducive to the longer cable runs required to reduce the fault current, or there may be voltage drop issues created by the long runs. Typically options a), b), and c) are considered first, in that order, before opting for d).

For our example option A) is chosen which has the least amount of system design changes. In order to select circuit breakers to achieve selective coordination the design engineer can refer to manufacturer published tables. The instantaneous region of the device bands tend to show an overlap on a TCC (plotted by most commercially available analysis software programs) for many circuit breakers because the curves have been based on the standalone characteristic curves for the maximum three-phase bus fault values. If dynamic impedance is considered for this region, then the fault current observed at the upstream circuit breaker may not be high enough to trip before the downstream circuit breaker reaches its maximum trip time for the manufacturers tolerances for instantaneous faults. Different combinations of circuit breakers can be tested to show coordination at or below certain fault values even though the software-generated TCC device bands overlap each other in the instantaneous region. Schneider Electric has published data bulletin 0100DB0501 - Short Circuit Selective Coordination for Low Voltage Circuit Breakers to present short circuit selective coordination data for various combinations of Schneider Electric low voltage circuit breakers. They were determined by comparing the current let-through of the downstream circuit breaker with the minimum instantaneous trip characteristic of the upstream circuit breaker, taking into account manufacturing tolerances. Thus the maximum level of selective coordination was determined for various pairings of upstream and downstream circuit breakers. Table 1 shows a table in 0100DB0501 for L-frame selectivity with QO and E-frame circuit breakers shows the option for upstream circuit breaker (PB2).



Based on the choices provided in Table 1, the new PowerPact L-W 400AF/125AT mission critical circuit breaker is selected. The circuit breaker LG-W selectively coordinates with circuit breaker EGB up to 30 kA at 480 V, which is higher than our available fault current of 11.857 kA. The LG-W mission critical circuit breaker has the same circuit breaker curve as LG trip 5.3A shown in our example in Figures 8 and 9, on Pages 14 and 15, respectively. The difference between L-Frame and L-Frame mission critical lies in their tripping mechanism; the L-frame mission-critical circuit breaker has an inherent 5 ms delay and, for high fault currents, operates on load-side energy rather than peak current. This effectively allows the J- and L-frame mission-critical circuit breakers to distinguish between load-side faults and let-through currents of load-side circuit breakers operating on faults. This energy-based tripping improves selectivity and has an arc flash advantage in that clearing time is not different than other molded case circuit breakers.

There is an additional data bulletin for transformer protection 0100DB0902 - Guide to Low Voltage Transformer Protection and Selective Coordination [2]. For a quick check Schneider Electric has an online selective coordination tool: click here. It does up to three levels of total selectivity look-up with user-input fault values or it can do simple fault calculations. The next coordination issue exists between circuit breakers PB4 and PB2 with AFN. The online selective coordination tool is used for selecting circuit breaker AFN as shown in the screenshots in Figures 6 and 7:

Table 1: Schneider Electric Selective Coordination Table for L-Frame Low-Voltage Circuit Breakers

Circuit Breaker Voltage Current One-Line DiagramMain Branch

L-W, 250 AQO(B0QO(B)-HQO(B)-VHQH

1060 A240 V

18

70125 A 10

L-W, 400 AL-W, 600 A

QO(B0QO(B)-HQO(B)-VHQH

15150 A 240 V 30

L-W, 250 AL-W, 400 AL-2, 600 A

E-Frame 115-125 A240 V 30 kA

480Y/277 30 kA



Figure 6: Screenshot of Schneider Electric Online Selective Tool



For this example the fault currents are manually filled in at three zones starting with Zone 1 22.507 kA at SWBD, Zone 2 14.816 kA at PNL1 and Zone 3 11.857 kA at PNL2, as shown in Figure 6. Based on the available fault current and circuit breaker types - EGB340 (PB4), LGUW3400-125AT (PB2), there are two options for circuit breaker AFN a) PG3400 and b) PK3400, as shown in Figure 7. Both options selectively coordinate with downstream circuit breakers up to 21.6 kA which is higher than our available fault current at Zones 1 and 2. However, option a) is selected based on lower short circuit withstand rating. The short circuit withstand rating of PG circuit breaker at 35 kA is adequate for the available fault current of 22.507 kA at Zone 1.

Figure 7: Result of Online Selectivity Tool for 3 Tier System



The only circuit breaker which is lacking selectivity on the normal side is the main circuit breaker SM1 in switchboard SWBD. Table 2 shows the table in 0100DB0501 for UL 480 Vac 400 A Selective Coordination. Based on Table 2, PowerPact RG 1200AT is selected as the main circuit breaker SM1. The RG circuit breaker has total selectivity with circuit breaker AFN-PG 400AT. With the help of Schneider Electric data bulletin 0100DB0501 and the online selectivity tool, total selectivity is achieved for the normal side of the system as shown in Figure 8.

Table 2: Schneider Electric Selective Coordination Table for 400 A / 480 Vac Downstream Circuit Breaker

Upstream Circuit Breaker Downstream Circuit Breaker - Type/kAIRMaximum Level of Selective Coordination Shown in kA

Maximum Continuous

Current Rating

kAIR TypeLA LA-MC LH

LH-MC DG DJ LD LG LJ LL LC LE LX LI LXI PG PJ PL

30 30 35 35 35 65 18 35 65 100 65 65 65 200 200 35 65 100

1200 A

35PG 21.6 21.6 21.6 21.6 35.0 35.0 18.0 35.0 35.0 35.0 35.0 35.0 35.0 35.0 35.0 21.6 21.6 21.3RG 30.0 30.0 35.0 35.0 35.0 35.0 35.0 35.0 35.0 35.0 35.0 35.0 35.0 35.0 35.0 35.0 35.0 35.0

50NT-NH 1200 A 30.0 30.0 35.0 35.0 35.0 50.0 18.0 35.0 50.0 50.0 50.0 50.0 50.0 50.0 50.0 35.0 35.0 35.0PK 21.6 30.0 35.0 35.0 35.0 50.0 18.0 35.0 50.0 50.0 50.0 50.0 50.0 50.0 50.0 21.6 21.6 21.6

65

NT-L1 1200 A 9.0 9.0 9.0 9.0 9.0 9.0 9.0 9.0 9.0 9.0 9.0 9.0 9.0 9.0 9.0 9.0 9.0 9.0NW-N 2000 A 30.0 30.0 35.0 35.0 35.0 65.0 18.0 35.0 65.0 65.0 65.0 65.0 65.0 65.0 65.0 35.0 35.0 35.0PJ 9.0 9.0 9.0 9.0 9.0 9.0 9.0 9.0 9.0 9.0 9.0 9.0 9.0 9.0 9.0 9.0 9.0 9.0RJ 30.0 30.0 35.0 35.0 35.0 65.0 18.0 35.0 65.0 65.0 65.0 65.0 65.0 65.0 65.0 35.0 40.8 40.8RK 30.0 30.0 35.0 35.0 35.0 65.0 18.0 35.0 65.0 65.0 65.0 65.0 65.0 65.0 65.0 35.0 65.0 51.3 NT-L 1200 A 9.0 9.0 9.0 9.0 9.0 9.0 9.0 9.0 9.0 9.0 9.0 9.0 9.0 9.0 9.0 9.0 9.0 9.0



After ensuring total selectivity for the normal side the emergency side of the system is evaluated. When fed from an emergency source, the panel PNL2 has an available fault current of 6 kA which is lower than 11.857 kA from normal source. Hence the devices selected for total selectivity for normal source will continue to have total selectivity when fed from the generator. Even though circuit breakers PB2 and PB4 have total selectivity amongst




themselves there is still cause for concern as circuit breaker AFE (LA 400AT) still lacks coordination with PB2 and PB4 as shown in Figure 3 on Page 6. The selection process for AFE is simplified by using the same circuit breaker as AFN. Both AFE and AFN are feeding the same load and as stated above the emergency source has lower fault current, so that what works for the normal side will continue to work for the emergency side.




The final coordination issues for the generator fed system are between circuit breaker GM1 and downstream devices. In Figure 3 on Page 6, the GM1 (PG 800AT) circuit breaker does not overlap with the downstream circuit breakers. The same does not hold true after the upgrade of downstream circuit breakers. We have to increase the short time and instantaneous settings of GM1 in order to avoid mis-coordination at the short time and instantaneous region. Figure 9 shows the new time current coordination graph for the emergency side of the system having total selectivity between the protective devices.

Arc Flash Analysis Arc flash analysis can be performed only after the protective devices have been adjusted for best possible coordination. With the help of a computer analysis through SKM Power Tools we are able to calculate the arc flash incident energy and categories at each piece of equipment. This is the most efficient way to calculate the incident energies and flash protection boundaries where multiple sources exist which must be taken into account (such as generators and motors). The SKM tool uses the National FIre Protection Association (NFPA) 70E 2012 Annex D.7 [3] and Institute of Electrical and Electronics Engineers (IEEE) 1584 [4] standards to determine the incident energy and arc flash boundaries.An arc flash analysis was performed for both normal and emergency side of the system with protective device settings as per Case 1 Load-based coordination where devices are selected based on

typical thermal-magnetic trips for circuit breakers other than service mains and prior to implementing NEC Article 100 requirement of selective coordination.

Case 2 Selective coordination to 0.1 seconds and longer Case 3 Total selective coordinationBased on the IEEE 1584 requirement for arc flash analysis both minimum and maximum three phase fault current have been considered. Arcing current is significantly lower than bolted current and based on typical calculations it can be as low as 52% of bolted fault current at 480 V [5]. Hence, to expect that total selectivity achieved at maximum three phase bolted current will yield optimized arc flash results at arcing current of minimum three phase bolted current is not reasonable, as shown in Table 3.

Table 3 shows a comparison between the arc flash results for Case 1, Case 2, and Case 3. From the table it is clear that, for a totally selectively coordinated system, the incident energy levels are significantly higher for the transfer switch 002L ATS, panels - 003 PNL1 and 004 PNL2. However, the arc flash incident energy remained the same for most equipment in Case 2 except for an increase in panel PNL1. The new instantaneous settings in both the cases resulted in higher trip time for the protective devices and thereby higher arc flash energy. This difference in incident energy and risk category in Case 2 and 3, is one of the reasons for preferring selective coordination to 0.1 seconds and longer, over, total selectivity. The increase in arc flash energy may pose a greater threat to personnel and could increase the amount of equipment damage in an arc flash event.



The arc flash incident energies of generator panel 001 GEN and main switchboard 005 SWBD do not change. This is because the results for both were based on maximum trip time of 2 seconds for all three cases. For the rest of the equipment (ATS, PNL1 and PNL2), there is considerable increase in incident energy as we go from load based coordination to selective coordination at 0.1 seconds and above and finally to total selective coordination. Hence, solely from an arc flash perspective, it is best to opt for selective coordination to 0.1 seconds and longer.

Conclusion In order to ensure reliability as well as safe working conditions, optimized selective coordination and arc flash mitigation have to work in tandem. The NFPA has already taken a step in that direction through NFPA 99-2012 [6] for health care facilities. NFPA 99-2012 requires that the essential electrical system be coordinated to 0.1 seconds for all types of fault current generated by the alternate source. In emergency, legally required, and critical operation power systems, NFPA 110-2010 [7] requires that the OCPDs feeding the automatic transfer switch(s) be selectively coordinated to the extent practicable. The IEEE color books Brown [8], Buff [9] and Orange [10], recognize the difficulty in achieving these opposing goals, and recommend selective coordination as far as practicable. The draft International Electrotechnical Commission (IEC) technical report [11] states that, Selectivity over the whole range of fault current up to the prospective fault current at the point of installation is not always possible or necessary. A more economic solution may be found in many cases by accepting a limited selectivity, particularly taking into account the low probability of a high short-circuit fault current.Schneider Electric recognizes the importance of worker safety by reduced incident energy and uninterrupted supply by improved selectivity, hence extensive research has been done to ensure both, and improve OCPD performance. One technique developed by Schneider Electric in each case a) in practice and b) in process of finalization, is as follows:A. Zone selective interlocking (ZSI) allows electronic trip devices to

communicate with each other so that a short-time trip or ground fault will be isolated and cleared by the nearest upstream circuit breaker with no intentional time delay. Devices in all other areas of the system (including upstream) remain closed to maintain service to unaffected loads. Without ZSI, a coordinated system results in the circuit breaker closest to the fault clearing the fault, but usually with an intentional delay. With ZSI, the device closest to the fault will ignore its preset short-time and/or ground fault delays and clear the fault with no intentional delay. Zone-selective interlocking eliminates intentional delay, without sacrificing coordination, resulting in faster tripping times. This limits fault stress by reducing the amount of let-through energy the system is subjected to during an overcurrent. At low voltage (600 V and below), Schneider Electric

Table 3: Arc Flash Comparison Table

Bus NameArc Flash Incident Energy in cal/cm2

(Case 1)

Required Protective Arc Rated Clothing Characteristics

(Case 1)

Arc Flash Incident Energy in cal/cm2

(Case 2)


(Case 2)

Arc Flash Incident Energy in cal/cm2

(Case 3)


(Case 3)001 GEN 12.44 Category 3 12.44 Category 3 12.44 Category 3002L ATS 0.51 Category 0 0.51 Category 0 11.91 Category 3003 PNL1 0.46 Category 0 9.80 Category 3 11.68 Category 3004 PNL2 0.38 Category 0 0.62 Category 0 2.37 Category 1005 SWBD 80.00 Dangerous 80.00 Dangerous 80.00 Dangerous



MasterPact low-voltage power circuit breakers, offer increased arc-flash protection due to faster clearing times, especially at higher current levels. In addition to superior arc-flash protection inherent in their design, MasterPact and PowerPact circuit breakers can be configured in a variety of Zone Selective Interlocking schemes to further enhance protection with no impact on selectivity. At higher voltages, SepamTM overcurrent relays can also be applied in ZSI solutions. (AF protections using ZSI is achieved only with the ST-ZSI option.)

Often ZSI is specified only within the main distribution board, though a more likely location for a fault occurrence is on a feeder circuit leaving the switchboard, or even lower in the system. To maximize the protection offered by using ZSI, as many levels of the system as possible need to be interlocked. This way, devices at the lower levels of the system will trip without any intentional delay, when necessary, without sacrificing coordination. This provides true selective coordination and maximum protection against fault stress. Additionally in certain areas of the system it is necessary to self-restrain a circuit breaker to maintain the delay before tripping during a fault condition. This results in the circuit breaker always introducing a time delay before tripping on a short circuit or a ground fault (the time delay is always activated). Cases where self-restraint should be applied are: The interlocked device is feeding a non-interlocked device

downstream (or a number of non-interlocked devices in a panel). A time delay is desired for short-circuit and/or ground-fault

occurrences (usually to avoid false tripping during transients and inrushes).

Minimal tripping time would compromise coordination.For more information on ZSI and self-restraint refer to data bulletin 06000DB0001 [12].

B. Energy based discrimination The new mission critical PowerPact J- and Lframe circuit breakers developed by Schneider Electric have energy based discrimination. The energy based method with its consistency allows the line-side circuit breaker to effectively distinguish between load-side faults and let-throughs of load-side circuit breakers operating on faults further downstream. This method for achieving selectivity uses supplemental trip systems in conjunction with specially designed primary trip systems. The primary trip system will not trip during the first half-cycle of a fault regardless of the fault current. The intentional delay that allows the reflex tripping to see load-side energy does not reduce overall clearing time, resulting in higher levels of selective coordination without necessarily unleashing higher levels of fault energy, including arc flash incident energy.For more information on energy based tripping refer to papers [13] and [14].



References [1] Short Circuit Selective Coordination for Low Voltage Circuit Breakers, 0100DB0501R01/12-03/12.[2] Guide to Low Voltage Transformer Protection and Selective Coordination, 0100DB0902R04/11-04/2011.[3] NFPA 70E-2012, Standard for Electrical Safety in the Workplace. [4] IEEE Std. 1584-2002, IEEE Guide for Performing Arc-Flash Hazard Calculations. [5] Arc Flash Hazard Calculations: Myths, Facts, and Solutions, H. Wallace Tinsley III, Michael Hodder, and Aidan M. Graham, IEEE Industry Applications Magazine, Jan/Feb 2007, originally presented at the 2006 IEEE/IAS Pulp and Paper Industry Conference, pp. 59, 60.

[6] NFPA 99-2012, Health Care Facilities Code.

[7] NFPA 110-2010, Standard for Emergency and Standby Power Systems. [8] IEEE Recommended Practice for Protection and Coordination of Industrial and Commercial Power Systems, IEEE Std 242-2001 (Buff Book), pp. 3-5, 607.[9] IEEE Recommended Practice for Power Systems Analysis, IEEE Std 399-1990 (Brown Book), pp. 367.[10] IEEE Recommended Practice for Emergency and Standby Power Systems for Industrial and Commercial Applications, ANSI/IEEE Std 446-1987 (Orange Book), pp. 175.[11] Draft IEC/TR 61912-2 Ed.1.0: Low-voltage switchgear and controlgear Overcurrent protective devices Selectivity under overcurrent conditions, International Electrotechnical Commission, March 23, 2007, committee draft updated after Copenhagen, pp. 11.[12] Reducing Fault Stress with Zone-Selective Interlocking, 0600DB0001R11/11-04/12.[13] Energy-based discrimination for low-voltage protective devices, Marc Serpinet and Robert Morel, Cahier Technique n 167, March 1998.[14] Energy Based Tripping and Its Effect on Selective Coordination, John Carlin & Josh Allen, Schneider Electric, May 2013.


Electrical equipment should be installed, operated, serviced, and maintained only by qualified personnel. No responsibility is assumed by Schneider Electric for any consequences arising out of the use of this material. 2013 Schneider Electric All Rights ReservedSchneider Electric, Square D, PowerPact are trademarks owned by Schneider Electric Industries SAS or its affiliated companies. All other trademarks are the property of their respective owners.

Schneider Electric USA, Inc.1415 S. Roselle RoadPalatine, IL 60067 USA1-888-778-2733www.schneider-electric.us

20

AbstractIntroductionSelective CoordinationArc Flash

Selective Coordination versus Arc Flash ExampleSelective Coordination Through Comparison of Time-Current CurvesArc Flash Analysis

ConclusionReferences

selective coordination vs arc flash requirements

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