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1Fundamentals of Circuit Protection101 Basics
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Fundamentals of Circuit Protection101 Basics
What are the 101 Basics?These modules provide an introduction to
various products and services available in the electrical control,
distribution and power quality categories.
The modules are organized by market segment and you can link
here to view a planning page to help select the modules that meet
your product and service knowledge needs.
What will you learn from this module?You will learn:
The types of circuit protection available. Codes and Standards
for circuit breakers. The five main components of circuit breakers.
The functionality of those five main components.
Included in this Module
Audio Option This module has an audio option if you would like
to listen to the material. You can turn off your speakers without
missing any of the key module concepts.
Printed MaterialsPrintable reference material is included in the
module attachments in case you want to take notes while working
though this material.
Knowledge ChecksThe knowledge check questions located throughout
the module are not included in your final module score.
AssessmentAn assessment is used to evaluate learning
effectiveness and will be your final module score.
Fundamentals of Circuit Protection101 Basics
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2Do you know the Fundamentals of Circuit Protection? Test your
knowledge. An 80% or better is required to pass this module.
Assessment
Welcome to Fundamentals of Circuit Protection. This module is
designed to increase your technical knowledge of circuit
protection.
Learn
Fundamentals of Circuit Protection101 Basics
The primary purpose of circuit protection is to protect the wire
from overheating in an
overcurrent situation, therefore limiting damage to the
equipment downstream of the protective
device.
Introduction
Exampleofaprotectivedevicethatfailed
Fundamentals of Circuit Protection101 Basics - Learn
What is Circuit Protection?
Circuit protection devices, also known as circuit breakers and
fuses, protect the wire and electrical equipment from fault
conditions including:
Overload FaultsShort Circuit FaultsSpecialty Faults (Ground
Fault and Arc Fault)
These protective devices were developed out of a need for safe
resettable devices that would be used as a means of disconnect in
facilities.
Fundamentals of Circuit Protection101 Basics - Learn
Objectives
By the end of this section, you will understand:
1. The purpose of circuit protection.
2. The types of circuit protection available in the market.
3. Difference between circuit breakers and fuses.
4. Codes and Standards for circuit breakers.
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3MoldedCase
MediumVoltageVacuumBreaker
Miniature
SupplementaryProtector
MediumVoltageFuse
LowVoltagePowerBreaker
PicturedisarepresentationofEatonscircuit
protectionoffering,inorderofincreasingvoltagecapacity.Types of
Circuit Protection
Fundamentals of Circuit Protection101 Basics - Learn
Fuse Protection
The purpose of a fuse is to protect the wire from overheating in
an overcurrent situation, therefore limiting damage to the
equipment downstream of the protective device.
Fuses are manufactured for low voltage through high voltage
applications and can be either current limiting or expulsion
type.
Fundamentals of Circuit Protection101 Basics - Learn
Eaton manufactures medium voltage fuses for use in medium
voltage assemblies. Eaton does manufacture devices that require low
voltage fuses (such as safety switches), however the low voltage
fuses are sourced from other manufacturers.
For more information on medium voltage fuses, see the Medium
Voltage Circuit Protection module.
Fuse Protection
As was defined previously, the purpose of a fuse is to protect
the wire from overheating in an overcurrent situation, therefore
limiting damage to the equipment downstream of the protective
device.
Fuses are manufactured for applications from low voltage through
high voltage and can be either current limiting or expulsion
type.
Eaton manufactures medium voltage fuses for use in medium
voltage assemblies. Eaton does manufacture devices that require low
voltage fuses (such as safety switches), however these are sourced
from other manufacturers.
For more information on fuses, see the following modules: Medium
Voltage Circuit Protection and Safety Switches.
Current Limiting FuseA fuse that when its current
responsive element is melted by a current within the fuses
specified
current limiting range, abruptly introduces a high resistance to
reduce
current magnitude and duration, resulting in subsequent
current
interruption.
Expulsion FuseA vented fuse in which the expulsion
effect of the gases produced by internal arcing, either alone or
aided
by other mechanisms, results in current interruption.
An expulsion fuse limits the duration of a fault on the
electrical system, not
the magnitude.
Eaton manufactures both current limiting and expulsion type
medium voltage fuses. More information can be found in the Medium
Voltage Circuit Protection module.
Fundamentals of Circuit Protection101 Basics - Learn
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4While the purpose of circuit breakers and fuses is the same,
there are fundamental differences to their designs, which are
important to understand when making selections for a system or
assembly.
Circuit Breaker
Resettable after a fault causes the circuit breaker to trip
Generally have a higher cost of initial investment Require regular
maintenance (specifically for low voltage power circuit and medium
voltage vacuum circuit breakers) Optional protective features (such
as ground fault)
Circuit Breakers vs. Fuses
Fuse
Must replace a fuse that is blown while interrupting a fault
Less initial cost of investment No maintenance required Only sense
overcurrent and do not have capability for optional protective
features
Fundamentals of Circuit Protection101 Basics - Learn
Codes and Standards
The electrical industry requires that circuit breakers are
designed and manufactured to meet codes and standards in order to
minimize the possibility and effects of fire and other risks.
These codes and standards can vary by country or by region. For
example, in the United States, the National Electrical Code can be
adopted, rejected or modified down to the state or municipal
level.
While standards can vary around the world, the impact that
standards have on the design and application of circuit breakers
worldwide is profound, and helps to ensure that the product is safe
for use in electrical systems.
Example of circuit breaker label meeting UL standards
Fundamentals of Circuit Protection101 Basics - Learn
United States Domestic Standards:Molded case circuit breakers
are designed, built, and tested in accordance with the NEMA and/or
Underwriters' Laboratories, Inc. (UL) standards.
Low voltage power circuit breakers are designed, built and
tested in accordance with the ANSI and/or Underwriters
Laboratories, Inc. (UL) standards. In addition, these breakers are
designed to be applied in accordance with the requirements of the
National Electrical Code (NEC).
Medium voltage vacuum circuit breakers are also certified to the
ANSI standard for North America.
International Standards:In addition to the above domestic
standards, international standards must be complied with in order
to sell products to world markets. There are many individual
country standards on circuit breakers, along with the International
Electrotechnical Commission (IEC) standards.
Additional details on standards can be found in Eatons catalogs
and Consulting Application Guide.
Codes and Standards
Fundamentals of Circuit Protection101 Basics - Learn
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Although low and medium voltage circuit breakers have unique
designs that are specific to amperage, voltage and application,
there are five main components that are universal across the
different types of circuit breakers.
Key Components of Circuit Breakers
FrameProtects internal parts of
circuit breaker from outside materials
Operating MechanismProvides a means of opening and closing the
circuit breaker
ContactsAllow current to flow
through the circuit breaker when closed
Arc ExtinguisherExtinguishes arc when circuit
breaker interrupts a fault
Trip UnitOpens operating mechanism in the event of a
prolonged
overload or short circuit
Fundamentals of Circuit Protection101 Basics - Learn
Objectives
By the end of this section, you will understand:
1. The five main components of circuit breakers.
2. The functionality of the main components.
This section will provide information on each component, its
functionality, and purpose.
Fast FactsThe interrupting rating of the circuit breaker is the
maximum amount of fault current it can interrupt without damaging
itself. The interrupting capacity of the circuit breaker must be
equal to or greater than the amount of fault current that can be
delivered at the point in the system where the circuit breaker is
applied.
The circuit breaker frame provides the rigidity and strength
required to successfully deal with the interruption process and
achieve the desired interrupting ratings.
It insulates and isolates the electrical current in order to
protect people and equipment during use or operation.
Frame
Metal Frame Molded Insulating Material
Fundamentals of Circuit Protection101 Basics - Learn
Click each frame to learn more:
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6Fast Facts
Theprimarypurposeofacircuitbreakeristoprotectthewirefromoverheating.
Provides the rigidity and strength required to successfully deal
with the interruption process and achieve the desired Interrupting
Ratings.
Provides for insulation and isolation of the current path,
offering personnel protection near the equipment during
operation.
Two Types of Frames:
Frame
Metal Frame Molded Insulating Material
Metal FrameAssembled from precise metal pieces that are bolted
and welded together to form the frame.
Some low voltage power circuit breakers and all medium voltage
vacuum circuit breakers are of the metal frame design.
Eaton offers the following circuit breakers in metal frames:
Low Voltage Power Circuit BreakersMedium Voltage Vacuum Circuit
Breakers
Fundamentals of Circuit Protection101 Basics - Learn
Fast Facts
Theprimarypurposeofacircuitbreakeristoprotectthewirefromoverheating.
Provides the rigidity and strength required to successfully deal
with the interruption process and achieve the desired Interrupting
Ratings.
Provides for insulation and isolation of the current path,
offering personnel protection near the equipment during
operation.
Two Types of Frames:
Frame
Metal Frame Molded Insulating Material
Molded Insulated Frame (aka Molded Case)Molded case frames are
made from strong insulating materials, such as glass-polyester or
thermoset composite resins (i.e. plastic frames).
Sizes vary according to the Ampere Rating of the circuit
breaker. Molded insulated material frames are primarily associated
with miniature, molded case and insulated case circuit breakers
(low voltage power circuit breakers designed to meet molded case
circuit breaker standards)
Eaton offers the following circuit breakers in molded case
frames:
Miniature Circuit BreakersMolded Case Circuit BreakersInsulated
Case Circuit BreakersLow Voltage Power Circuit Breakers
Fundamentals of Circuit Protection101 Basics - Learn
Operating Mechanism
Fundamentals of Circuit Protection101 Basics - Learn
Click each type of operating mechanism to learn more.
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7Operating MechanismOver Toggle Operating Mechanism
The function of the operating mechanism is to provide a means of
opening and closing the circuit breaker.
This toggle mechanism is the quick-make, quick-break type,
meaning that the speed with which the contacts snap open or close
is independent of how fast the handle is moved.
In addition to indicating whether the breaker is ON or OFF, the
operating mechanism handle indicates when the breaker is tripped by
moving to a position midway between the ON and OFF.
Eatons residential, miniature and molded case circuit breakers
utilize over-toggle mechanisms.
Fundamentals of Circuit Protection101 Basics - Learn
Operating MechanismTwo Step Stored Energy Operating MechanismThe
two-step stored energy mechanism is used when a large amount of
energy is required to close the circuit breaker and when it needs
to close rapidly.
The major advantages of this mechanism are rapid reclosing and
safety. Rapid reclosing is achieved by storing charged energy in a
separate closing spring. Safety is achieved by providing remote
charging of the spring.
Fundamentals of Circuit Protection101 Basics - Learn
The two-step stored energy process is designed to charge the
closing spring and release energy to close the circuit breaker. It
uses separate opening and closing springs. This is important
because it permits the closing spring to be charged independently
of the opening process. This allows for an open-close-open duty
cycle. The closing spring can be charged (or recharged) manually
via a charging handle or electrically via a motor. The motor can be
operated remotely, allowing maximum safety for the operator.
Eatons low voltage power circuit breakers and medium voltage
vacuum circuit breakers utilize two-step stored energy
mechanisms.
Contacts are found in the arc interruption chamber (in low
voltage circuit breakers) and in the vacuum interrupter (in medium
voltage vacuum circuit breakers)
The contact assembly consists of the movable contact, the
movable contact arm, the stationary contact and the stationary
conductor (as pictured).
Contacts
As the circuit breaker opens or closes, the fixed contact
maintains its position while the movable contact moves to close
(make) or open (break) the circuit.
The contacts are designed to protect against two fault
conditions:- Overcurrent (thermal overload)- Short Circuit
(magnetic)
Movable contact arm
Stationary contact arm
Fundamentals of Circuit Protection101 Basics - Learn
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8An arc extinguisher is the component of the circuit breaker
that extinguishes an arc when the contacts are opened.
An arc is a discharge of electric current crossing a gap between
two contacts. Circuit breakers must be designed to control them
because arcs cannot be prevented.
Arc Extinguisher
The next section will cover what an arc is and methods to
extinguish the arc in a circuit breaker.
Real World Example of an Arc:Have you ever pulled a plug out of
an electrical socket while the appliance is still turned on and
seen what appeared to be sparks? What you were observing, on a very
small scale, was an attempt at arc formation between the wall
contacts and the plug contacts in your hand.
Fundamentals of Circuit Protection101 Basics - Learn
Arcs are formed when the contacts of a circuit breaker open due
to larger than normal current.
The size of the arc depends on the amount of current present
when the contacts are pulled apart. Because arcs cannot be
prevented, circuit breakers must be designed to control them.
What is an Arc?
The heat associated with an arc creates an ionized gas
environment. The more ionization, the better the conditions for an
arc to be maintained and grow. The bigger the arc, the greater the
potential for damage to the circuit breaker and electrical
distribution system.
Arcing is a condition that must be dealt with quickly and
effectively by a circuit breaker. The ability of the circuit
breaker to control the arc is key to its short circuit interrupting
capability.
Fundamentals of Circuit Protection101 Basics - Learn
Listed below are the six methods used in the electrical industry
to manage electrical arcs:
Arc ChuteVacuum InterrupterSF6Minimum OilMagnetic CoilPuffer
Eaton manufactures circuit breakers using Arc Chute and Vacuum
Interrupter technologies. The next slides will go into more detail
on these two types of technologies.
Arc Control Methods
Fundamentals of Circuit Protection101 Basics - Learn
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9Listed below are the six methods used in the industry to deal
with arc control:
Arc ChuteVacuum InterrupterSF6Minimum OilMagnetic CoilPuffer
Eaton manufactures circuit breakers using Arc Chute (for low
voltage breakers) and Vacuum Interrupter (for medium voltage
breakers) technology. Those two methods will be covered in this
course.
Arc Control Methods
Click the pictures to learn more about the two methods
Arc Chute Technology (also known as Arc Extinguisher)The
function of the arc chute is to confine, quench, split, and
extinguish the arc drawn between the circuit breaker contacts each
time a circuit breaker interrupts current.
In order to interrupt high, short circuit faults, and dissipate
the large amount of energy, the arc chute consists of specially
shaped steel plates isolated from each other and supported by an
insulating housing (as pictured).
When the contacts are opened, the arc induces a magnetic field
in the steel plates which, together with other magnetic forces and
gas flow, draws the arc into the plates. For an arc with current
below about 6000 amperes, the arc usually splits into a series of
smaller arcs by the plates and is extinguished rapidly.
Arc Chutes
Eaton uses arc chute technology in residential, miniature,
molded case and low voltage power circuit breakers. Note Not all
residential and miniature circuit breakers utilize an arc
chute.
Fundamentals of Circuit Protection101 Basics - Learn
Listed below are the six methods used in the industry to deal
with arc control:
Arc ChuteVacuum InterrupterSF6Minimum OilMagnetic CoilPuffer
Eaton manufactures circuit breakers using Arc Chute (for low
voltage breakers) and Vacuum Interrupter (for medium voltage
breakers) technology. Those two methods will be covered in this
course.
Arc Control Methods
Click the pictures to learn more about the two methods
Shown is an animation of an arc chute extinguishing an arc
during an overload.
Fundamentals of Circuit Protection101 Basics - Learn
Listed below are the six methods used in the industry to deal
with arc control:
Arc ChuteVacuum InterrupterSF6Minimum OilMagnetic CoilPuffer
Eaton manufactures circuit breakers using Arc Chute (for low
voltage breakers) and Vacuum Interrupter (for medium voltage
breakers) technology. Those two methods will be covered in this
course.
Arc Control Methods
Click the pictures to learn more about the two methods
Vacuum Interrupter TechnologyVacuum interrupter technology uses
enclosed contacts to extinguish arcs.
The vacuum interrupter is a pair of contacts (primary contacts)
enclosed in a vacuum-tight envelope (also known as bottle). The
bottle itself is a ceramic material with a metal end plate brazed
to each end. The metal plates seal the ends and provide support for
the parts inside.
Because the environment inside the interrupter bottle is a
vacuum, an arc cannot be easily sustained and is extinguished
within the bottle.
One vacuum interrupter is provided for each pole of a circuit
breaker.
Eaton uses vacuum interrupter technology for medium voltage
vacuum circuit breakers.
Vacuum Interrupter Bottle
Fundamentals of Circuit Protection101 Basics - Learn
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10
Trip Unit
The function of a trip unit is to trip (open) the operating
mechanism in the event of a prolonged overload or short circuit
fault condition, such as:
Thermal OverloadShort Circuit Currents (Magnetic / Short Circuit
Currents)Specialty Faults (Ground Fault, Arc Fault)
To accomplish this, an electromechanical or a solid state trip
unit is provided.
The differences between these two trip units will be explored
after defining the different types of fault conditions.
Fundamentals of Circuit Protection101 Basics - Learn
ThermalOverloadProtection
Magnetic/ShortCircuitProtection
SpecialtyFaultProtection
Usesacircuitbreakertoterminatepowertothe
circuitifanoverload/overcurrent
eventoccurs.
Anelectricalfaultthatiscreatedwhentwo
exposedconductorstouchorwhenaconductors
insulationfails.
Specialtyfaultprotectionis usedinspecific
applicationsbasedoncodesandstandards.ArcFaultCircuit
Interrupters
andGroundFaultProtectionaretwoofthemostcommontypes.
Click on each type of fault protection to learn more
Types of Fault Protection
Fundamentals of Circuit Protection101 Basics - Learn
ThermalOverloadProtection
Magnetic/ShortCircuitProtection
SpecialtyFaultProtection
Thermalprotectionisachievedthroughtheuseofabimetalelement
(consistingoftwostripsofmetalbondedtogether)
heatedbytheloadcurrent.
Magneticprotectionisachievedthroughtheuseofanelectromagnetinserieswiththeload
current.
Specialtyfaultprotectionis usedinspecific
applicationsbasedoncodesandstandards.ArcFaultCircuit
Interrupters
andGroundFaultProtectionaretwoofthemostcommontypes.
Click on each type of protection to learn more.
Types of Overload Protection Thermal Overload Protection
Thermal trip action is achieved through the use of a bimetal
element heated by the load current. A bimetal element consists of
two strips of metal bonded together. Each strip has a different
thermal rate of heat expansion.
Heat due to excessive current will cause the bimetal to bend or
deflect. The metal having the greater rate of expansion will be on
the outside (longer boundary) of the bend curve.
To trip the circuit breaker because of a sustained overload, the
bimetal must deflect far enough to physically push the trip bar and
unlatch the contacts, as pictured.
Fundamentals of Circuit Protection101 Basics - Learn
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11
ThermalOverloadProtection
Magnetic/ShortCircuitProtection
SpecialtyFaultProtection
Thermalprotectionisachievedthroughtheuseofabimetalelement
(consistingoftwostripsofmetalbondedtogether)
heatedbytheloadcurrent.
Magneticprotectionisachievedthroughtheuseofanelectromagnetinserieswiththeload
current.
Specialtyfaultprotectionis usedinspecific
applicationsbasedoncodesandstandards.ArcFaultCircuit
Interrupters
andGroundFaultProtectionaretwoofthemostcommontypes.
Click on each type of protection to learn more.
Types of Overload Protection Thermal Overload Protection
(continued)
Deflection of the bimetal is predictable as a function of
current and time.
This means that a typical 100 ampere circuit breaker might trip
in 1800 seconds at 135% of rating (Point A), as shown in the
picture.
Consequently, bimetals provide a long time delay on light
overloads (Point A), yet have a fast response on heavier overloads
(Point B).
Thermal elements are calibrated at the factory and most are not
field adjustable. Typically a specific thermal element must be
supplied for each current rating.
Time Current Curve
Fundamentals of Circuit Protection101 Basics - Learn
ThermalOverloadProtection
Magnetic/ShortCircuitProtection
SpecialtyFaultProtection
Thermalprotectionisachievedthroughtheuseofabimetalelement
(consistingoftwostripsofmetalbondedtogether)
heatedbytheloadcurrent.
Magneticprotectionisachievedthroughtheuseofanelectromagnetinserieswiththeload
current.
Specialtyfaultprotectionis usedinspecific
applicationsbasedoncodesandstandards.ArcFaultCircuit
Interrupters
andGroundFaultProtectionaretwoofthemostcommontypes.
Click on each type of protection to learn more.
Types of Overload Protection Magnetic / Short Circuit
Protection
Magnetic trip action is achieved through the use of an
electromagnet in series with the load current.
When a short circuit occurs, the fault current passing through
the circuit causes the electromagnet in the circuit breaker to
attract the armature, initiating an unlatching action, in turn
causing the circuit to open.
The only delaying factor is the time it takes the contacts to
physically open and extinguish the arc.
Fundamentals of Circuit Protection101 Basics - Learn
ThermalOverloadProtection
Magnetic/ShortCircuitProtection
SpecialtyFaultProtection
Thermalprotectionisachievedthroughtheuseofabimetalelement
(consistingoftwostripsofmetalbondedtogether)
heatedbytheloadcurrent.
Magneticprotectionisachievedthroughtheuseofanelectromagnetinserieswiththeload
current.
Specialtyfaultprotectionis usedinspecific
applicationsbasedoncodesandstandards.ArcFaultCircuit
Interrupters
andGroundFaultProtectionaretwoofthemostcommontypes.
Click on each type of protection to learn more.
Types of Overload Protection Magnetic / Short Circuit Protection
(continued)
That action takes place in less than one cycle (0.016 seconds),
and trips the breaker instantaneously. See top picture for a
typical magnetic trip curve. The breaker will not trip until the
fault current reaches or exceeds Point A.
The magnetic trip element may be fixed or adjustable, depending
upon the type of breaker and frame size.
Each adjustable magnetic trip is calibrated at the factory for a
specific range and is set on the high side. Knobs located on the
front of the trip unit can be adjusted to specific requirements.
The knobs have a high, a low, and a series of intermediate setting
positions. See bottom picture for a typical set of magnetic trip
curves, illustrating how the adjustment knobs move the curve from
left to right as the magnetic trip is increased.
Tim
e Cu
rrent
Cur
ve fo
r Fix
ed
Mag
netic
Act
ion
Tim
e Cu
rrent
Cur
ve fo
r Ad
just
able
Mag
netic
Act
ion
Fundamentals of Circuit Protection101 Basics - Learn
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12
ThermalOverloadProtection
Magnetic/ShortCircuitProtection
SpecialtyFaultProtection
Thermalprotectionisachievedthroughtheuseofabimetalelement
(consistingoftwostripsofmetalbondedtogether)
heatedbytheloadcurrent.
Magneticprotectionisachievedthroughtheuseofanelectromagnetinserieswiththeload
current.
Specialtyfaultprotectionis usedinspecific
applicationsbasedoncodesandstandards.ArcFaultCircuit
Interrupters
andGroundFaultProtectionaretwoofthemostcommontypes.
Click on each type of protection to learn more.
Types of Overload Protection Specialty Fault Protection
Arcing faults, a common cause of many home electrical fires, can
occur when insulation around cords, wires or cables is damaged or
deteriorated.
Designed to prevent fires by detecting a non-working (i.e.,
non-intended/non-useful) electrical arc and disconnecting the power
before the arc starts a fire.
The National Electrical Code (NEC) requires the installation of
combination-type AFCIs in all 15 and 20 ampere residential circuits
with the exception of the laundry room, kitchen, bathrooms, garage
and unfinished basement.
Arc Fault Circuit Interrupter Ground Fault Circuit
Protection
Designed to protect against electrical shock, in cases where one
phase goes to ground.
National Electrical Code (NEC) requires ground fault protection
in applications such as:
Residential: Anywhere electricity can come into contact with
water, i.e. bathrooms, laundry room, kitchen Industrial: Any
assembly where there may be phase to ground loss
Ground fault circuit protection is not available in an
electromagnetic trip unit and must be included in a separate
device.
Can be included as an option in an electronic trip unit.
Fundamentals of Circuit Protection101 Basics - Learn
Electromechanical (Thermal Magnetic) Trip Units
Electromechanical trip units are commonly used in low voltage
circuit breakers.
They utilize bimetals and electromagnets to provide overload and
short circuit protection and are commonly referred to as thermal
magnetic trip units.
Thermal Magnetic trip units do not include any specialty
protection, such as ground fault. If ground fault protection is
required, you may need to select an electronic trip unit or include
separate ground fault protection within the system.
Fixed Trip Unit
Interchange-able
Trip Unit
Eatons Thermal Magnetic Circuit Breaker offering is as
follows:Miniature, Residential, Supplementary Protectors Fixed (can
not be replaced) Trip UnitMolded Case Circuit Breakers - Fixed or
Interchangeable (replaceable) Trip Unit
Fundamentals of Circuit Protection101 Basics - Learn
Electromechanical (Thermal Magnetic) Trip Units
Thermal magnetic trip units include the features of both the
thermal and magnetic protection, as pictured top.
Points A and B on the trip curve, bottom picture, illustrate
both the thermal and magnetic action on a typical 100 ampere
circuit breaker. A 250% overload would take 60 seconds before the
bimetal would deflect far enough to hit the trip bar and open the
circuit (Point A).
However, if instead of an overload there was a short circuit
that was 4000% (40 times) the circuit breaker rating, the
electromagnet in the circuit breaker would attract the armature and
trip the circuit breaker in approximately one cycle (0.016
seconds)(Point B).
Fundamentals of Circuit Protection101 Basics - Learn
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13
Electronic Trip Units
Electronic trip units offer capabilities such as programming,
monitoring, diagnostics, communications, system coordination and
testing that are not available on thermal magnetic trip units.
Thus, we are seeing more electronic trip units and electronic
protective relays specified over conventional electromechanical and
thermal magnetic trip units for circuit breakers.
The result being increased accuracy, repeatability,
discrimination, temperature independence and built-in ground fault
protection for the electrical system.
Clickforexamplesof
EatonsElectronicTripUnits
Almost all electronic trip units employ microprocessor based
technology that provides true RMS current sensing for correlation
with thermal capacity of conductors and equipment, as opposed to
bimetals that are used in thermal magnetic trip units.
Fundamentals of Circuit Protection101 Basics - Learn
Electronic Trip Units
Electronic trip units offer capabilities such as programming,
monitoring, diagnostics, communications, system coordination and
testing that are not available on thermal magnetic trip units.
Thus, we are seeing more electronic trip units and electronic
protective relays specified over conventional electromechanical and
thermal magnetic trip units for circuit breakers.
The result being increased accuracy, repeatability,
discrimination, temperature independence and built-in ground fault
protection for the electrical system.
Clickforexamplesof
EatonsElectronicTripUnits
Almost all electronic trip units employ microprocessor based
technology that provides true RMS current sensing for correlation
with thermal capacity of conductors and equipment, as opposed to
bimetals that are used in thermal magnetic trip units.
Fundamentals of Circuit Protection101 Basics - Learn
Eatons molded case circuit breakers and low voltage power
circuit breakers utilize Electronic Trip Units (ETU).
Molded Case ETULow VoltagePower Breaker ETU
Protective Relays
Clickforexamplesof
EatonsProtectiveRelays
Medium voltage vacuum circuit breakers do not have an integrated
trip unit, differentiating them from low voltage circuit
breakers.
In this case, the circuit breaker handles the power flow and the
overcurrent protection requirements are handled by external
protective relays.
Overcurrent, undervoltage, differential, lockout, and timing
relays are just a few different types of functions that exist.
Fundamentals of Circuit Protection101 Basics - Learn
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14
Electronic Trip Units
Electronic trip units offers capabilities such as programming,
monitoring, diagnostics, communication, system coordination and
testing that are not available on thermal magnetic trip units.
Thus, we are seeing more electronic trip units and electronic
protective relays specified over conventional electromechanical and
thermal magnetic trip units for circuit breakers.
The result being increased accuracy, repeatability,
discrimination, temperature independence and built-in ground fault
protection for the electrical system.
Clickforexamplesof
EatonsElectronicTripUnits
Almost all electronic trip units employ microprocessor based
technology that provides true RMS current sensing for correlation
with thermal capacity of conductors and equipment, as opposed to
bimetals that are used in thermal magnetic trip units.
Eatons medium voltage vacuum circuit breakers utilize external
protective relays.
Example of switchgear and medium voltage vacuum circuit
breaker
Fundamentals of Circuit Protection101 Basics - Learn
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Now that the five main components of circuit breakers have been
defined, we will identify those components on Eaton circuit
breakers. Note These are examples and not to scale. Not all circuit
breakers are designed the same.
Click each type of circuit breaker for a closer look at its
components.
Identifying Components on Circuit Breakers
MiniatureCircuit Breaker
Molded CaseCircuit Breaker
Low VoltagePower
Circuit Breaker
Medium VoltageVacuum
Circuit Breaker
Fundamentals of Circuit Protection101 Basics - Learn
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15
Now that the four main components of circuit breakers have been
defined, we will identify those components on Eaton circuit
breakers. Click each type of circuit breaker for a closer look at
its components.
Introduction
MiniatureCircuit Breaker
Molded CaseCircuit Breaker
Low VoltagePower
Circuit Breaker
Medium VoltageVacuum
Interrupter
Miniature Circuit Breaker
Molded Frame
Operating Mechanism
Contacts
Trip Element
Remember Not all residential and miniature circuit breakers
utilize an arc chute.
Fundamentals of Circuit Protection101 Basics - Learn
Now that the four main components of circuit breakers have been
defined, we will identify those components on Eaton circuit
breakers. Click each type of circuit breaker for a closer look at
its components.
Introduction
MiniatureCircuit Breaker
Molded CaseCircuit Breaker
Low VoltagePower
Circuit Breaker
Medium VoltageVacuum
Interrupter
Molded Case Circuit Breaker
Molded Frame
Operating Mechanism
Arc Extinguisher
Contacts
Trip Unit
Fundamentals of Circuit Protection101 Basics - Learn
Now that the four main components of circuit breakers have been
defined, we will identify those components on Eaton circuit
breakers. Click each type of circuit breaker for a closer look at
its components.
Introduction
MiniatureCircuit Breaker
Molded CaseCircuit Breaker
Low VoltagePower
Circuit Breaker
Medium VoltageVacuum
Interrupter
Low Voltage Power Circuit Breaker
FrameNote - Arc
Extinguisher and Contacts are located behind the interface.
Operating Mechanism (Charging Handle)
Trip Unit
Fundamentals of Circuit Protection101 Basics - Learn
-
16
Now that the four main components of circuit breakers have been
defined, we will identify those components on Eaton circuit
breakers. Click each type of circuit breaker for a closer look at
its components.
Introduction
MiniatureCircuit Breaker
Molded CaseCircuit Breaker
Low VoltagePower
Circuit Breaker
Medium VoltageVacuum
Interrupter
Medium Voltage Vacuum Circuit Breaker
Metal Frame
Vacuum Bottle (includes arc
extinguishing function and contacts)
Operating Mechanism
Remember These circuit breakers utilize external protective
relays.
Fundamentals of Circuit Protection101 Basics - Learn
Module Summary
After reviewing the material in this module, you should now
understand:
The purpose of circuit protection. The types of circuit
protection available in the market. The difference between circuit
breakers and fuses. Codes and Standards for circuit breakers. The
five main components of circuit breakers. The functionality of the
main components.
Fundamentals of Circuit Protection101 Basics - Learn
Assessment
This is the final section of this module. If you have any
comments or suggestions about this module please email
[email protected]
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Fundamentals of Circuit Protection101 Basics - Assessment
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17
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