Abstract: Information is provided for selecting the proper circuit breaker for a
particular application. This recommended practice helps the application engineer
specify the type of circuit breaker, ratings, trip functions, accessories, acceptance
tests, and maintenance requirements. It also discusses circuit breakers for special
applications, e.g., instantaneous only and switches. In addition, it provides
information for applying circuit breakers at different locations in the power system,
and for protecting specific components. Guidelines are also given for coordinating
combinations of line-side and load-side devices.
Keywords: circuit breakers, circuit breaker evaluation, insulated case, insulatedcase circuit breakers, low-voltage circuit breaker, low-voltage power circuit
breaker, low-voltage protection, low-voltage protection device, molded case,
molded-case circuit breaker, overcurrent protection, power circuit breaker, rating,
testing
CONTENT
Chapter 1
Overview
1.1 Scope
1.2 Two classifications of breakers
1.3 Description of a molded-case circuit breaker
1.4 Description of a low-voltage power circuit breaker
1.5 Document organization
1.6 Summary.
1.7 Normative references
1.8 Bibliography
Chapter 2
Definitions, acronyms, and abbreviations
2.1 Definitions
2.2 Acronyms and abbreviations
2.3 Normative references
2.4 Bibliography
Chapter 3
Rating and testing
3.1 Relevance of rating and testing
3.2 The ideal circuit breaker
3.3 The practical circuit breaker
3.4 Basic circuit-breaker selection criteria
3.5 The role of industry standards
3.6 The role of safety and industry codes
3.7 Comparison of testing requirements
3.8 Circuit-breaker classes and types
3.9 Generalized application considerations
3.10 References on rating and application
3.11 Endurance considerations
3.12 Circuit-breaker voltage rating considerations
3.13 Frequency rating and considerations
3.14 Temperature considerations
3.15 Enclosure considerations
3.16 Cable, wire, and conductor considerations
3.17 De-rating for ambient temperature
3.18 Circuit-breaker humidity limitations
3.19 Circuit-breaker altitude limitations
3.20 Circuit-breaker ampere rating
3.21 National Electrical Code considerations
3.22 Preferred current ratings
3.23 Load effects
3.24 The effect of nonlinear loads on circuit breakers
3.25 The effect of high inrush loads
3.26 Overload testing of circuit breakers
3.27 Forced-air cooling of LVPCBs
3.28 Short-circuit interrupting rating
3.29 Fault-current calculation considerations
3.30 Circuit-breaker interrupting ratings
3.31 Single-pole fault interruption testing
3.32 Circuit-breaker evaluation in standards for testing
3.33 Blow-open contact arms
3.34 Circuit breaker useful life
3.35 Considerations on interrupting duty and maintenance
3.36 Integrally fused devices
3.37 Series-connected rating
3.38 Cascade arrangement
3.39 Short-time rating
3.40 Circuit-breaker evaluation for X/R ratio or short-circuit power factor
3.41 Single-pole interrupting capability and power system design
considerations
3.42 Applying ac thermal-magnetic molded-case circuit breakers using
their UL 489 dc rating
3.43 Normative references
3.44 Bibliography
Chapter 4
Specific applications
4.1 Scope
4.2 Selection considerations
4.3 Selection approach for application requirements
4.4 Selection approach for electrical ratings
4.5 Modifications and accessories for specific applications
4.6 Normal versus abnormal conditions
4.7 Considerations for applying MCCBs, ICCBs, and LVPCBs
4.8 Service requirements and protection
4.9 Main circuit breakers
4.10 Tie circuit breakers
4.11 Feeder protection
4.12 Normative references
4.13 Bibliography
Chapter 5
Selective coordination of low-voltage circuit breakers with other protective devices
5.1 Introduction
5.2 Low-voltage power circuit breakers
5.3 Low-voltage MCCBs and ICCBs
5.4 Other coordinating devices
5.5 Coordination examples
5.6 Normative references
5.7 Bibliography
Chapter 6
Fused and special-purpose circuit breakers Introduction
6.2 Instantaneous-trip circuit breakers
6.3 Mine-duty circuit breakers
6.4 Current-limiting circuit breakers
6.5 Molded-case switches
6.6 Fused circuit breakers .
6.7 Circuit breaker and ground-fault circuit interrupter
6.8 Arc-fault circuit interrupter
6.9 Supplementary protectors
6.10 Normative references
6.11 Bibliography
Chapter 7
Acceptance and maintenance requirements Scope
7.2 Maintenance program
7.3 Maintenance of MCCBs
7.4 Maintenance of LVPCBs
7.5 Maintenance and testing of ICCBs
7.6 Maintenance and testing of molded-case switches
7.7 Maintenance of ground-fault circuit interrupters (GFCIs)
7.8 Documenting maintenance results
7.9 Testing program
7.10 Failures detected
7.11 Normative references
7.12 Bibliography
Annex 7A (informative) MCCB data
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