circuit_breakers(1).pdf

Table of Contents

Introduction...............................................................................2

Need.for.Circuit.Protection........................................................4

Types.of.Overcurrent.Protective.Devices..................................8

Circuit.Breaker.Design.............................................................

Types.of.Circuit.Breakers.........................................................23

Circuit.Breaker.Ratings............................................................27

Time-Current.Curves...............................................................29

Selective.Coordination.............................................................32

Series-Connected.Systems.....................................................34

Siemens.Circuit.Breakers........................................................37

Residential.Circuit.Breakers.....................................................38

Panelboard.Circuit.Breakers....................................................46

General.Purpose.Thermal-Magnetic.Circuit.Breakers..............49

Solid-State.Trip.Unit.Circuit.Breakers.......................................56

Internal.Accessories................................................................62

External.Accessories...............................................................65

VL.Circuit.Breakers.................................................................. 7

WL.Circuit.Breakers................................................................79

Review.Answers.....................................................................84

Final.Exam...............................................................................85

quickSTEP.Online.Courses......................................................88

Introduction

Welcome.to.another.course.in.the.STEP.series,. S iemens.

T echnical. E ducation. P rogram,.designed.to.prepare.our.

distributors.to.sell.Siemens.Energy.&.Automation.products.

more.effectively..This.course.covers. Basics of Circuit Breakers .

and.related.products..

Upon.completion.of. Basics of Circuit Breakers .you.will.be.able.

to:

•. Explain.the.need.for.circuit.protection

•. Identify.various.types.of.overcurrent.protective.devices

•. Explain.the.basic.electro-mechanical.operation.of.a.circuit.

breaker

•. Identify.various.types.of.Siemens.circuit.breakers

•. Identify.circuit.protection.ratings.for.various.types.of.

Siemens.circuit.breakers

•. Describe.time-current.characteristics.on.a.time-current.

curve

•. Explain.the.benefits.and.function.of.circuit.breaker.

coordination

•. Identify.internal.and.external.circuit.breaker.accessories

This.knowledge.will.help.you.better.understand.customer.

applications..In.addition,.you.will.be.better.able.to.describe.

products.to.customers.and.determine.important.differences.

between.products..You.should.complete. Basics of

Electricity before.attempting. Basics of Circuit Breakers ..An.

understanding.of.many.of.the.concepts.covered.in. Basics of

Electricity .is.required.for. Basics of Circuit Breakers ..

If.you.are.an.employee.of.a.Siemens.Energy.&.Automation.

authorized.distributor,.fill.out.the.final.exam.tear-out.card.and.

mail.in.the.card..We.will.mail.you.a.certificate.of.completion.if.

you.score.a.passing.grade..Good.luck.with.your.efforts.

Siemens.is.a.trademark.of.Siemens.AG..Product.names.

mentioned.may.be.trademarks.or.registered.trademarks.of.their.

respective.companies..Specifications.subject.to.change.without.

notice.

National Electrical Code ®.and. NEC ®.are.registered.trademarks.

of.the.National.Fire.Protection.Association,.Quincy,.MA.0269-

747..

Portions.of.the. National Electrical Code® .are.reprinted.with.

permission.from.NFPA.70®,. National Electrical Code® .

MA.0269..This.reprinted.material.is.not.the.complete.and.

official.position.of.the.National.Fire.Protection.Association.

on.the.referenced.subject,.which.is.represented.only.by.the.

standard.in.its.entirety.

NEMA®.is.a.registered.trademark.and.service.mark.of.the.

National.Electrical.Manufacturers.Association,.Rosslyn,.VA.

22209.

Underwriters.Laboratories.Inc.®.and.UL®.are.registered.

trademarks.of.Underwriters.Laboratories.Inc.,.Northbrook,.IL.

60062-2096.

Other.trademarks.are.the.property.of.their.respective.owners.

Need for Circuit Protection

Current and Temperature .

Current.flow.in.a.conductor.always.generates.heat..The.greater.

the.current.flow,.the.hotter.the.conductor..Excess.heat.is.

damaging.to.electrical.components.and.conductor.insulation..

For.that.reason,.conductors.have.a.rated.continuous.current.

carrying.capacity.or. ampacity ..Overcurrent.protection.devices,.

such.as. circuit breakers ,.are.used.to.protect.conductors.from.

excessive.current.flow..These.protective.devices.are.designed.

to.keep.the.flow.of.current.in.a.circuit.at.a.safe.level.to.prevent.

the.circuit.conductors.from.overheating..

Normal Current Flow

Excessive Current Flow

Excessive.current.is.referred.to.as. overcurrent ..The. National

Electrical Code® (NEC®) .defines.overcurrent.as. any current in

excess of the rated current of equipment or the ampacity of a

conductor .. It may result from overload, short circuit, or ground

fault (Article.00-Definitions).

Reprinted with permission from NFPA 70®, National Electrical Code®,

This reprinted material is not the complete and official position of the

National Fire Protection Association on the referenced subject, which is

represented only by the standard in its entirety.

Overloads .

An. overload .occurs.when.too.many.devices.are.operated.on.

a.single.circuit,.or.a.piece.of.electrical.equipment.is.made.to.

work.harder.than.it.is.designed.for..For.example,.a.motor.rated.

for.0.amps.may.draw.20,.30,.or.more.amps.in.an.overload.

condition..In.the.following.illustration,.a.package.has.become.

jammed.on.a.conveyor,.causing.the.motor.to.work.harder.and.

draw.more.current..Because.the.motor.is.drawing.more.current,.

it.heats.up..Damage.will.occur.to.the.motor.in.a.short.time.if.

the.problem.is.not.corrected.or.the.circuit.is.shut.down.by.the.

overcurrent.protector.

Conductor Insulation .

Motors,.of.course,.are.not.the.only.devices.that.require.circuit.

protection.for.an.overload.condition..Every.circuit.requires.some.

form.of.protection.against.overcurrent..Heat.is.one.of.the.major.

causes.of.insulation.failure.of.any.electrical.component..High.

levels.of.heat.can.cause.the.insulation.to.breakdown.and.flake.

off,.exposing.conductors..

Good Insulation

Insulation Affected by Heat

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