Figure 2 represents a system composed of three circuit breakers defined as devices a, b and c. Selective coordination for critical systems per the 2014 nec. For lowvoltage power circuit breakers to moldedcase circuit breakers mccb, coordination values are derived from time current curves with instantaneous in off position for power circuit breaker. Evaluating selective coordination between currentlimiting fuses and non currentlimiting circuit breakers steve hansen senior field engineer robert lyons jr. The appearance of the internet version of this manual. Selectivity, back up protection and coordination guide eaton. This collection of selectivity and backup tables for abb circuit breakers has been studied to help select the appropriate circuit breaker, fulfilling the specific selectivity.
Circuit breakers are designed to break discontinue the flow of electricity to protect people and equipment when current reaches an unsafe level due to overload, short circuit, or other electrical faults. Introduction with the inclusion of new language in the 2005 national electrical code nec, the requirements for selective coordination of electrical power systems are, at present, more stringent than. Circuit breakers must trip quick enough to avoid equipment or wiring failure, but not so fast as to give false, or. Additional resources these documents contain additional information concerning related products from rockwell automation.
Series c gframe molded case circuit breakers time current. Calculate the rating of the incoming circuit breaker, size of incoming and load cables and coordination of cascaded circuit breakers mccbs in switchboard. Follow row to right to obtain the downstream panelboard branch circuit breaker typeand the largest possible branch circuit breaker. Use of motor protection circuit breakers with variable. Selective coordination study recommended procedures. Merlin gerin circuit breaker application guide mm m m m m m m m m m m m merl in ger in multi 9 c60n c63 4 0va 6 0 0. The selective coordination analysis tool provides you with the ability to select combinations of circuit breakers that provide total selective coordination.
The study gathered a multitude of opinions of global trading venues and thus serves as further input to this important topic. Coordination for low voltage circuit breakers is utilized, along with tcc comparisons where necessary. Proper coordination requires a comparison of the operating characteristics of. Timecurrent curves are typically shown on a loglog plot. In this post i will address some frequently asked questions and misconceptions regarding means for achieving high levels of selective coordination with molded case circuit breakers mccbs q. Discrimination with lv power circuit breakers the purpose of this cahier technique is to set out the discrimination techniques which apply specifically to low voltage power circuit breakers.
In the example on the right with breaker coordination, the breaker. Use of motor protection circuit breakers with variablefrequency drives introduction a motor branch circuit, including a variable frequency drive vfd and one or more motor protection circuit breakers mpcbs, is a complex system and its performance depends on all co mponents, devices, configuration and their interconnection. Typical coordination of transformers, fuses, relays, and breakers. Motor protection circuit breaker and motor circuit protector. When growth occurs, the ampacity may be increased up to the circuit breaker s maximum. Coordination capabilities micrologic circuit breakers can coordinate with each other and with power monitoring systems. The 5sl miniature circuit breakers are intended for use up to 6 ka10 ka. Low voltage breaker fuse coordination requires a minimum 0. When the circuit breaker is closed, a complete path for current exists between the voltage source and the motor allowing the motor to run. Selective coordination note 1, issue 1 evaluating selective coordination between currentlimiting fuses and non currentlimiting circuit breakers steve hansen senior field engineer robert lyons jr. Coast guard marine safety center 3 circuit breakers with magnetic or instantaneous trips will only coordinate with each other if there is.
A circuit breaker coordination study is used to analyze the tripping times for the series of overcurrent devices being compared, generally from the source through the largest branch circuit device. Circuit breakers equipped with solidstate trip devices can be tested using secondary current injection, which requires less time and expense to perform the test. When a short circuit or overload occurs, upstream breakers are tripped, unnecessarily knocking out circuits and equipment, which also makes it more difficult for maintenance personnel to locate the source of the fault. How do you know if a circuit breaker will work when it is called upon to interrupt an electrical fault or short circuit.
These devices are characterized by their high rating 800 a to 6300 a, and their location at the head of the lv installation, generally directly. Shortcircuit, coordination, and arcflash studies for data. The example on the left lacks breaker coordination. Circuit breaker curves indicate that only a 32a breaker will discrim with 100a fuses. Pdf design of protection coordination for overcurrent on.
Effective february 2020 supersedes january 2020 circuit. Opening the circuit breaker breaks the path of current flow and the motor stops. Tqd and tjd breakers are complete with cual line and load lugs. The space requirements for this article do not allow for a detailed explanation of the analysis methods. This includes circuit breaker coordination analysis for each generator. Methods for coordinating system protective equipment, december. The versatility of the adjustments on an electronic trip circuit breaker offers the designer a multitude. Molded case circuit breakers section 6 how to order qline thermal magnetic circuit breakers moldedcase switches the product number as shown in the following pages includes the complete breaker or switch. Protective device coordination protective device coordination study description. Guide to power system selective coordination 600v and below document number 0100db0603 2. Determine the maximum available fault current from all sources, at both the line and load side breakers, by means of a short circuit study, appropriate charts andor formulas. How to design an electrical system in which the upstream protective device fuse or circuit breaker nearest to the system fault clears the fault without affecting the protective devices that are upstream from it. Circuit breaker characteristic trip curves and coordination.
The minimum instantaneous unlatching current for the 400 a circuit breaker could be as low as 2000 a times. Selection of the protection system for machines and plants 28 9. Design of protection coordination of a distribution network. Figures along the horizontal axis of the curve represent the. Generalities about the main electrical parameters of the protection and control 7 3.
With the basics now covered, one can confidently approach those topics. The curves are a logarithmically graphical representation of the performance characteristics of the devices at a base voltage of 480 volts. These circuit breakers must open and break the current as quickly as possible. As can be seen in the figure the available single line to ground fault is about 105% of the available three phase. This tool provides circuit breaker selections that are fully rated and fully selective. Evaluating selective coordination between currentlimiting. The devices are applied at three different fault current values. Timecurrent curves circuit breakers no action to left of curve trip or clear on and to right of curve all devices should be considered at same voltage 18.
Properly engineered and installed selective coordination. Provides guidance to engineers regarding the national electrical code nec requirements for selective coordination. A circuit breaker is a device that allows automatic opening of a circuit in response to overcurrent, and also manual opening and closing of a circuit. They comprise multiple tables for main or upstream and branch breakers. The curve below shows a 90ampere circuit breaker and an upstream 400ampere circuit breaker with an instantaneous trip setting of 5 5 times 400 a 2000 a. Molded case circuit breakers 3 moldedcase circuitbreakers section 3. From the coordination table, the selectivity value, i s, is 10 ka between the two circuit breakers. Our selective coordination lookup tables are quick and easy to use. Tripping time for the circuit breakers in sailing condition at one typical disturbance are 0.
Ed frame circuit breakers are used in individual enclosures, switchboards, panelboards, and load centers. Depending on the specific circuit breaker, sentron series circuit breakers are available as a molded case switch, instantaneous magnetic trip circuit breaker motor circuit protection, or thermal magnetic circuit breaker which provides complete overload and short circuit protection. As long as the circuit breaker type and maximum size are adhered to and the available fault current. For total coordination tables, the maximum available fault current at downstream panelboardis given also. The curve below shows a 90 ampere circuit breaker and an upstream 400 ampere circuit breaker with an instantaneous trip setting of 5 5 times 400a 2000a. Circuit breaker coordination using trip curves for coordination circuit breaker coordination is the process of selecting and applying circuit breakers in an electrical distribution system to localize a fault condition and restrict power outages to the equipment affected. For a branch circuit fault current less than 3600a on the loadside of the 100a circuit breaker, the 400a and 1200a circuit breakers will be coordinated with the 100a circuit breaker. Pdf article characteristics of circuit breaker trip. Circuit breakers that have thermalmagnetic or electromechanical trip units can only be verified for correct functioning via the primary current injection test method. Circuit breaker selective coordination tables eatn. A circuit breaker can be chosen based on projected growth, and by changing the longtime pickup, its ampacity can be reduced down to 20% of its maximum. Frequently asked questions about selective coordination. Trip curves represent the predicted behavior of a circuit breaker in a cold state ambient room temperature. Ge energy industrial solutions ge overcurrent device.
Bulletin 140m motor protection circuit breakers mpcbs are ulcsa listed as type e manual selfprotected combination motor controllers or ulcsa listed as circuit. In the uncoordinated system there is overlap of the circuit breaker trip curves, and in some instances the main circuit breaker will trip before the feeder circuit breaker. The inclusion of selective coordination in the nec since the 2002 revision and the. Siemens circuit breakers describe timecurrent characteristics on a timecurrent curve explain the benefits and function of circuit breaker coordination identify internal and external circuit breaker accessories explain the difference between molded case circuit breakers and insulated case circuit breakers. Simply match the required main and branch circuit current ratings and select the combination based on the available short circuit current. E 150 line thermal magnetic circuit breakers magnetic circuit. This paper specifically addresses how to comply with these requirements for lowvoltage circuit breakers. How to achieve selective coordination of circuit breakers eep. Circuit breakers for naval shipboard use pg01218003ejanuary 2010.
It can be seen the coordination is done in such a way that circuit breaker 4 has to operate first followed by fuse and finally relay. V4t21 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 molded case circuit breakers learn online drawings online series g circuit breakers. Tcc curves for fuse and circuit breakers were observed. Characteristics of circuit breaker trip curves and coordination. This type of coordination is a further evolution of time coordination and can be direct or indirect. Selective coordination tables published by the circuit breaker manufacturer indicate the maximum level of available fault current to which pairs of circuit breakers achieve selective coordination for all values of time even below 0. Although 20 of 29 responding exchanges 69% generally favor the con. Notice the overlap of the 200 ampere fuse and 20 ampere circuit breaker. A complete breaker consists of frame, trip, and one line and one load lug per pole. Designing for circuit breaker instantaneous selectivity. Overcurrent coordination page 3 qualtech engineers, inc. Timecurrent curves are essential for the proper coordination of circuit breakers.
Designing for selective coordination specifying engineer. They are also suitable for the quick and easy mounting of additional components, such as auxiliary switches and fault signal contacts. The breaker speed, relay settings, and recloser characteristics are selected in a manner to interrupt the fault current before a series fuse i. This is the zone in which the thermal protection for thermomagnetic releases and protection l for electronic releases are normally called on to intervene. Is a 32a breaker the max that can be used under 100a fuses in order to properly discriminate and comply with the above clause. If the fault current is greater than 3600a, then the 400a feeder circuit breaker may unnecessarily open and there is a lack of coordination. Designing for circuit breaker instantaneous selectivity robert p. Characteristics of circuit breaker trip curves and. This means that if the maximum prospective short circuit current on the load side of the 1492spm 8a circuit breaker is less than 10 ka.
Two specifications for selective coordination are considered. Molded case circuit breaker selectivity guide in this example figure 2, we consider a 60 a 140gj breaker. Circuit breaker coordination simplified method with time current curve with the simplified method, there is no need to have the unlatching times or draw the unlatching curves. In the event of a fault, only the circuit breaker closest to the fault should operate, leaving other circuits unaffected.
The following curve illustrates the time current characteristics for the 1200a circuit breaker, the 400a circuit breaker and 100a circuit breaker. The following circuit breakers are derived from eaton, westinghouse, or cutlerhammer brand. Motor protection circuit breaker and motor circuit. When the design begins to mix fuses and circuit breakers in the distribution system, designing for selective coordination is more difficult.
Breaker coordination refers to the use of breakers specificallyincluding the latest electronic trip breakersto isolate electrical problems, stop nuisance tripping. These devices have system features that are characteristic of all siemens miniature circuit breakers. Motor protection circuit breaker and motor circuit protector specifications multiple motor installation with mpcbs each motor has an individual branch circuit protective device. Coast guard marine safety center 3 circuit breakers with magnetic or instantaneous trips will only coordinate with each other if there is adequate impedance between them such that the. Guide to power system selective coordination 600v and below.
Fuses circuit breakers systems with fuse and circuit breaker mixture mandatory selective coordination requirements why selective coordination is mandatory selective coordination system considerations ensuring. The following curve illustrates a typical thermal magnetic molded case circuit breaker curve with an overload region and an. The transformers are assumed to be close coupled to the switchgear. Circuit breaker circuit breaker in the sentron series family. Example for coordination of cascaded circuit breakers. Pdf article characteristics of circuit breaker trip curves. Short circuit and protection coordination studies introduction.
Ed frame circuit breakers are available as a molded case switch, instantaneous magnetic trip circuit breaker. Shortcircuit, coordination, and arcflash studies for. The result is a set of tables which allow for easy and efficient selection of square d panelboards and their overcurrent devices. There is support for greater coordination of circuit breakers across venues. Timecurrent curves are used to show the amount of time required for a circuit breaker to trip at a given overcurrent level. The circuit breaker will open automatically during a fault, or can be manually opened. Tripping sequence and tripping time of devices were observed.
Time current curves are engineering reference documents for application and coordination purposes only. Selective coordination with circuit breakers iaei magazine. Medium voltage products technical guide protection. To determine if proper coordination exists between molded case circuit breakers, a comparison of circuit breaker characteristic trip curves is necessary. Selective coordination between the feeder and branch circuit is not attainable for faults above 2500 amperes that occur on the 20 amp branch circuit, from lp1. Circuit breakers a survey among international trading venues. For field testing molded case circuit breakers, refer to nema ab 4 guidelines series c gframe 15100 amperes, 120480 volts. Communication between circuit breakers at different levels in the system allows the downstream circuit breaker clos est to the fault to ignore its preset delay time and trip without any intentional time delay on a short circuit or. Microversatrip pm trip unit the microversatrip pm trip unit adds power management system capability, advanced metering, and protective relays to the basic. Short circuit, coordination, and arcflash studies for data centers fig. Jun 28, 2018 generate short circuit, devise settings, sqop reports.
Circuit breakers for overload protection of household and similar. Selective coordination selective coordination cooper bussmann. The other circuitbreakers must be capable of withstanding the thermal and electrodynamic stresses related to the passage of the fault current for the intentional iv coordination tables discrimination and backup. Circuit breaker a and circuit breaker b need to be selective up to 30ka, circuit breaker b and circuit breaker c need to be selective up to ka. Do shortcircuit current study and coordination study use time current curves to identify types and options of cbs required to achieve selective coordination select breaker needed eliminate overlap of curves for fault current available even small changes in fault current can result in lack of compliance shortcircuit current study by. How to achieve selective coordination of circuit breakers.