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Miniature

circuit breakers

Low Voltage Products & Systems

I

Miniature circuit breaker

Application guide

Index

Miniature circuit breaker application guide

............................................. 1 - 8

General information

Selective coordination and series ratings

Miniature

circuit breakers II

Low Voltage Products & Systems

Notes

Miniature

circuit breakers

Low Voltage Products & Systems

Miniature circuit breaker

Application guide

Introduction

Overload

Thermal Example

10A

Breaker

Light15A

The light draws more than 10 amps for

an extended period of time creating a thermal overload.

Short circuit

of

Magnetic Example

10A

Breaker

Light10A

The wire connected between the light and

breaker is cut and shorted to ground creating a short circuit.

Breaker definition

situations; Overload and Short Circuit.

ABB current limiting breaker

Tripping lever

Operating

mechanism

Operator

Electro-magnetic protection

Upper terminal

Thermal protection-bimetal

Arc chamber Fixed contact

Moving

contact

DIN rail holderLower terminal

Space for identification marker

AG: General information

Miniature

circuit breakers

Low Voltage Products & Systems

Circuit breaker construction

Thermal / Magnetic trip units definition

contacts.

Overload protection

Magnetic trip units (short circuit protection)

Components of a magnetic trip unit

Current Flow During Operation

All highlighted components are energized during operation

Magnetic Trip UnitThermal Trip Unit

Trip Bar

Operating Mechanism

Thermal Trip Unit

Armature and Plunger

Movable Contact

Magnet Trip Unit

Miniature

circuit breakers

Low Voltage Products & Systems

Circuit breaker construction

Arc runners / Arc chutes

segment does not have a high enough energy level to maintain an arc

Breaker curves

Thermal Trip Unit

Magnetic Trip Unit

Breaker Contacts

This region of the curve is the time required for the contacts of the

Arc RunnerArc Chute

Magnetic Trip Unit

(Region Two)Thermal Trip Unit(Region One)

Moving Contacts

(Region Three)

Miniature

circuit breakers

Low Voltage Products & Systems

Circuit breaker current limitation

Current limiting definitions

as current

UL AC 60Hz cycle

UL breaker current limiting

NEC240.2 current limiting

reduces the current ?owing in the faulted circuit to a magnitude

IEC 60947-2 current limiting circuit breaker

reached.

ABB current limiting breakers

milliseconds.

Zero point extinguishing breakers

milliseconds.

Current limiting breakers and electrical networks

Current Limitation

cycle and limit the amount of current that can reach a circuit. Limiting IsqT

The true destructive nature of a short

square of the current. The magnetic forces vary as a square of the th relatively small magnitude in a extremely short time, which dramatically

Miniature

circuit breakers

Low Voltage Products & Systems

Circuit breaker current limitation

Current limiting and zero crossing breakers

into an arc chute that extinguishes the arc. for the waveform to cross zero. When the wave form crosses zero the

Current limiting example

Zero crossing example

50
0 -50 0 V U-L 2

100 /di

v -40 0 -30

0-200-100100200

30
0400
kSampl e499.93 Sample/div 10 -1 0 kA I-L 2

2 k/di

v -8 -6-4-224 68

Time A Time B

Legend

Voltage

Amps 50
0 -50 0 V

U-BCP L

2

100 /di

v -40 0 -30

0-200-100100200

30
0400
kSampl e499.93 Sample/div 10 -1 0 kA I-L 2

2 k/di

v -8 -6-4-224 68

Time A Time B

Legend

Voltage

Amps

Miniature

circuit breakers 6

Low Voltage Products & Systems

Selective coordination and series ratings

IEC 60497-1 selective coordination definition

Example of breaker coordination

Example of no breaker coordination

coordination is easier to achieve with the use of current limiting Selective coordination and current limiting breakers

Selective coordination and zero crossing breakers

for There are a few manufactures that have achieved coordination Main breaker

CB1CB2CB3CB4

Short circuit

AG: Selective coordination and series ratings

Miniature

circuit breakers

Low Voltage Products & Systems

Selective coordination and series ratings

Series ratings -vs- selective coordination

Selective coordination

Selective coordination is achieved when there is a short circuit on a

Example

Series ratings

Example

Main breaker 65 kA
CB1

10 kACB210 kACB310 kACB410 kA

35 kA or 65 kA short circuit

AG: Selective coordination and series ratings

Miniature

circuit breakers

Low Voltage Products & Systems

mechanism

Thermal

Fixed contact

Lower terminal

Miniature circuit breaker components

Miniature

circuit breakers

Low Voltage Products & Systems

Notes

Miniature

circuit breakers

Low Voltage Products & Systems

Notes

ABB Inc.

ABB Inc.

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