Electrical Circuit Breakers
PART 1-R
This is the first in a series of Articles Intended to Supplement
Your Knowledge Beyond The Immediated Requirements of the NEC. The Series will Cover the
Types of Circuit Breakers that are found in various types of facilities today. The Beginning
Article Lays A Foundation (a Review for Many) and Progresses to intropiCing Molded Case,
Insult Case, and Drawout Types with the Series ending with the most Advanced of All,
Microprocessor-Based Circuit Protective Devices. The Follow Topics Are Cover in this
The first part of the server:
Circuit Breakers defined
Circuit Breakers as Switches
Current levels to be broken
Over-Currents
Current and Temperature
Circuit Breakers As High Tempeature Limit Switches
Ampacities of Electrical Conductors
Short Circuits
Shorts to group
Arcing faults
Bolted faults
SafeTy First, Always First
NEC Requirements for Circuit Breakers
This part of the servers by hard
THEN DELVES INTO SOME of the Nice to Know Details About the Relationships of Current,
Temperature, and ampacities of confrs.
of faults is then cover.
Being of First Order Importance.
Of the General NEC Requirements Related to Circuit Breakers. To Minimize the Lendth of
This painting, only automatic circuit breaker type overcurrential deviceS are cover.
RESTATED, FUSES, and Motor Starter Type Overload Relays Are Not Covered.
Initially Those Electrical Giants, Edison and Tesla; Had only
Lead Wire Fuses to Protect the Messelves and their Equipment from Overcurrents. Gazing Into
That fog that is the future, Perhaps we will see the deviceS Become Increasingly More
Intelligent, and General Circuit Protective Devices Taking on AdDitional Task as System
Monitors.
Circuit Breakers defined
The American National Standards Institute (ANSI) defines a
Circuit Breaker as: A MeChanical Switching Device, Capable of Making, Carrying and and and and AND
Breaking Currents Under Normal Circuit Conditions. Also Capable of Making and Carrying
For a Specify Time and Breaking Currents Under Specified Abnormal Circuit Conditions,
such as aSESE of A Short Circuit. The NEC DEFINES A CIRCUIT BREAKER as a Device
Designed to open and close a circuit by non-minatic means, and to open the circuit automatically
on a Predetermine Overcurrent with Damage to itset where
Rating. While The And the NEC Definitions Describe the Same Family of Devices,
They do have some disfreences; the ame is true with the actual circuit breakers they.
They are much the say in general terms; however, there are a number of significant
Between The Many Types of Electrical Circuit Breakers Installed in Various Types of Facilities
Today.
Circuit Breakers as Switches
Both the ANSI and the NEC Definitions AcKNowledge The Potential
for the leggImate Use of Circuit Breakers as Switches. Swices that Pass But
Do not consume electrical enricy) are considered as being control devices; this one may
Also say that a breaker is a control device, or a controller.
And Protect An Electrical Circuit and People Operating the Utilization Equipment. An Electrical
Relay is an exmple of an operationing control; it opens and closes the circuit. Circuit
Breakers are not designed as replacements for operating controls such as relateds, contactors,
OR MOTOR Starters.
There is, as you may have intuitively anticipated, an exception.
SOME CIRCUIT BREAKERS Are Manufactured for Use in a Specific Type of Application. WHEN
A Circuit Breaker is Designed to Also Be Routinely Use as An on-Off Switch to Control
120 or 277Volt Florescent Luminaires they are marked SWD, for switch duty. This does not
Mean that a switch duty breaker can be used to manually control a traffic signal light
Where it will be cycld on and off 1,000 or more timers per day.
for switch duty (SWD) DOES Not Mean A Circuit Breaker Can Be USED AS A High Frequencycy
CyCling Operating Control, Such as a Relay that has a life span rate in tens, if not
Hundreds of the Thousands of Duty Cycles.
While Circuit Breakers Can Be Legitimately and Safly Use
AS SWITCHES, The Frequency and Duration of Such Use is Limited. Routinely Circuit Breakers
Are Manually Operated for Service-Maintenance and Repair Type Activities. With the Presenting
enhancing our undertnds, we can say that clear breakers can leggimately be userd
As Switches; General They Are Not Intended for Prolonged Repetitive Manual Breaking
And Making Type Control of Electrical Energy Utilization Equipment.
Current levels to be broken
For general considation, and our immiedia
Amounts of Current Circuit Breakers are required to open can be divled into the follow
Three Broad Current Amplitude Groups.
The first and logest is rated load or less. For exmple: a
60 Amp Low Voltage Molded Case Thermal-Magnetic Breaker Must Be Able to Open or Close
AT 48 AMPS (80% of its rate) or less.
Next up in Currentity, this same breaker must be
To open overload level CurrenTs. Overloads for Our Purposes Can Be UNDERSTOOD BY Reference
to the necrirements for overload profrs. Thermal overloads are commit
Sized for some 115% of the motor s nameplate full load amps. a motor with a service
Factor of One, HAVING A ROAD LOAD of 10 AMPS WOULD Be Overloaded WHEN PULLING 11.5 AMPS
ORORE. Overload Currents Can for Our Immediated Purposes Be Considered to Be Percentages
Increases Above Rated Normal Load Current.
The Third and Highest Current Level Group is Short Circuit
Currents. Short Circuit (FAULT) Currents can be considered as being Fifteen (15) or more
Times normal rated loadurrents.
In Summation, Circuit Breakers May Be Called to Open Open or
Close a Circuit Within A Range of from No Current Flow to As Much as Fifteen (15) Times
OR MORE ITS Rated Current. For A 100 AMP BREAKER that Could 1,500 AMPS or More.
As will be capered Later, this high value of short circuit
Current is routinely Exceeeded by Circuit Breakers Today.
As IMPLYING that Circuit Breakers can open unlimited amounts ofurrent. As will be for
Later on, they can not.
Over-Currents
The National Electrical Code (NEC) Defines Overcurrent as Any
Current in Excess of the Rated Current Of The Equipment or The Ampacity of a Conductor.
Overcurrent (or Excessive Current) Conditions are caused by
Defective ConDactor Insulation, Defective Equipment, or An Excessive Workload Burden Placed Placement
upon the utilization equipment and its electrical circuit. Fuses and Circuit Breakers
PROVIDE A Level of Safety Against Overcurrent Conditions in Electrical Circuits. We therefore
ROUTINELY says and Circuit Breakers are overcurrent propive devices (OCPD).
That is, they proterly the circuit s components from too much current.
Hopefully This Papaerhopefull
Current and Temperature
The Movement of Electricity in A Conductor Produces
a Rise in the TEMPERANAR
InSuration. Excessive Temperator Rise (Cauised by An Excessive Amount of Electron Collisions
With Base Material Atoms) Can Result in the Melting of the Wires Material (assumed to
be copper by the nec). If it is allowed to rise as high as 1,980 Degrees f. for a pointt
of Reference, The NEC LIMITS The Operation Temperance of xhhw Type Conductor Insulation
To No more than 194 Degrees F. Thus It can be under the long before the copper wire
Will Begin to Melt, The Wires Insulation Material Will Have Melty, and Perhaps Even Burned
up.
OUR FIRST Priority, thereffore, is the temporature of the confctor s
Electrical Insulating Materials. Different Types of Insulating Materials Have Different
maximum design Operating Temperatures.
Circuit Breakers As High Tempeature Limit Switches
Electrical Energy is Transported Throughout An Electrical Circuit
by the condition, patelvided by Electrically Insulaced Wires.
The Insulation function in the circuit has a high temporarian
The Copper Wire. Circuit Breakers are Routinely Sized to Limit Thermal Energy Related
DAMAGE to the Electrical Insulation Material and Not the Copper Wire.
We can say that a circuit breaker limits the testure of the connected-propty wire s
Insulation materials.
Ampacities of Electrical Conductors
Just How Hot An Electrically Insulated Wire Can Get Before
ITS Insulation Melts, SUFFERS DAMAGE, ORS A Decrease in Electrical Dielectric Strengength
(The Abilital to Perform as an Electrical Insulator) Are Well-Known Facts. The various
Types of Materials used as electrical insulation have ben tested and the results listted
in what are called ampages in the nec in article 310.16.
How long anstalled consider inSuration
Material Will Last Without Overload is Yet Another Question. Research is underway to determine
The life of an insulated conflic.
MANY FATORS that has a negative impact upon the inspact update life of an insulated contentor.
For now we can book a SAFE BET that Voltage Spikes, Vibration, ENVIRONMENTAL FACTORS Such
As temporary, Dust Both Electrly and Thermally Conductive and Non-Conductive Types,
Uv Light, Aggressive Vapors and Fluids, and Relative Humidity Will All Be Proven to Shorten
to some degree the life of modeln plastic type electrical insparalials.
I SUSPECT that Many of the Same Factors Also Have a Negative
Impact Upon Circuit Breakers.
of circuit breakers. NOR am I aware of any research underway seeking to determine the
Service Life of Circuit Breakers. Considering the Importation of the Safety PROVIDED to
People and proprTy that circuit breakrs provides, it is a bit puzzling as to why super
Research has not alream ben underrTaken.
For Many Years Various Types of Materials Have Been Use as
Electrical Insulators. TODAY Conductors Are Made USING MATERIAL for Outr Jacketing and
For Filling in the Gaps (Indices) Between Bundled Round Conductors. These Materials May
Or may not be considered to be electrical insulators. Some Medium and High Voltage Cables
Are Made USING MATERIALS that are considerd to be consortuctive, or semi-conductive. SOME
Low Voltage Instrumentation, Control, and Signal USAGE TYPE Cables Are Made with A Layer
Of ConDuctive Material that acts as a shield to draw static electrical charges.
Short Circuits
A Short Circuit is an University
Can flow. Any timeurrent flows in a path that is not the normal path, we say that the it
Circuit is shorted. Shorts are further defined by the nature of the shorted connection.
A Direct Short is Commonly a Phase-To-PHASE Short, which is when two hot (un-glass)
Wires Make Unintended Contact with Each Other; a Phase-To-PHASE Short Circuit Has Thus
Been Created.
A circuit breaker must be able to respond to a short city,
Which Can Present a Large Current Flow in a Short Period of Time. A Short Circuit University
an overload (Typically A Percentage Increase of Rated Load Current) PRESEENTS ITSELF
a very short period of time and will typically be multiples of the load s normal
operatingurrent.
Breakers are tested to determine their about to clear a short
Circuit with damage to theMselves. With a Phase-to-PHASE Short, The Breaker Will Be
Required to open the circuit at the circuit s rate-to-pHASE VOLTAGE. This
Would be the case independent of the system the system bebing group or un-glass is either.
Wye or Delta solidly grouped or un-founded or Resistance (IMPEDANCE) grouped.
Shorts to group
When an insulated hot wire (un-founded) un-intentionally makes
Electrical Contory with An Electrical ConDuctive-Grounded Object, A Group Fault Is
create.
InSuration; and the Faulted Wire has shorted to group. Many Times a Phase-TO-PHASE Short
Willopopop inTo a Group, and the Other Way Art. Either a Phase-to-PHASE Short
Can produce a group fault, or a group fault can produce a phase-to-pHase short.
FAULT Can Be in One, Two, or Three Wire S Insulation Materials.
Group fault type cycuit breakers (GFCI) Will not be
in this painting. The Short Circuit, Overload Currenting Limiting Nature of the Types of Breaker,,
However, Will be covered. It is only the group or residual current feature of gfci
Type Breakers that is not capered. A Group can devert can be a Current Flow that is Limited
ONLY by the Impedance of the Circuit and the Capacity of the Energy Source Supplying The
Faulted Circuit. Group Faults Can Occur Rapidly and Can Be Either a Low Impedance Type,
Developing a significant amount of electrical Energy, or as an arcing type fault with
Little Total Energy Consumed.
To arcing type shorts to group.
Circuit Breakers Typically Will Respond to a Short to Group
That is of the low image,
To which the circuit breaker has ben manuFactured to see and then respond to.
When installed in a grounded system, such as a center grouped
Wye System, only about one half of the system s phase-to-pHASE VOLTAGE will be broken
by the breaker on a ground type fault. With an un-Fined Type System A GROUND FAULT
On the first phase-to-glass connection do result in anycurnt flow as the system
is not referenced to group. Yet Should a Second Ground Fault Develop, The Breaker Will
Be required to break pHase-to-pHASE SYSTEM ROTED VOLTAGE.
With Resistance Group Systems, The Impedance of the Supply
System S Group and the Circuit S Group Combine to Determine the Amount
of Current Drawn. FURTHER, More Detailed Pursuit of UNDERSTANDINGHON
System Group (Earthing) Methods Use in America Is Beyond The Limiting Scope of this
Paper. I Suggest that you read more on grouping, as it is a subject that seems to always
Open Up Disagreements. Mr. Holt S Book Titled Group and Bonding, NEC 250, (Product
# O2NCT2) is just out and cachers this topic much better than I have so done.
Arcing faults
When a loose connection (a gap) is made in the faulted circuit
so loose that the carrent flow is non-Continuous, it is class an arcing or arc fault.
This type of circuit defect is Much Like A Welder USING A WELDING ELECTRODE to Produce
an Electric Arc. Arcing Type Faults Are the Most Difficult to Locate (Due to ConDuctor
Concealment in Conduit or Inside of Walls and their Non-Continuous Nature)
The cause of fires. This type of defect is the opposite of a bolted fault; the city
Impedance is Higher and the Connection is very Irregular (High Frequency).
Flows for only a frame of a second and then cools down and may not flowurrent, or or or
Heat Up Again and Produce An Arc Across the Gap Between The Two Conduction Surfaces.
During the anc Cycle there are two times that the support circuit
VOLTAGE Goes to Zero Volts; there are two times when the city s electromotive
Pressure is Zero and An Arc Cannot Be Produced. This zero Volts Time Helps to Increase
The faulted circuit s imageance. This higher image makes it more disticult for
The Arc to Re-Establish itset again. These types of faults product heat in a very small
Area. They can start a fire and not try a common thermal-magnetic circuit breaker
Their Energy Level is so low and they last for such a short time that they are typically
Not Responded to by a Common Circuit Breaker.
In Response to this unique type of circuit defract, a new family
of Circuit Protectors Called Arc Fault Circuit Interrupter (AFCI) Type Circuit Breakers
Has Been Under Development Over for The Last Ten Years.
(MicroComputers) of the Devices they will not be capered in this short paper.
Circuit Breaker Will Not Respond to the Development of An Arcing Type Fault Due to the
Low Total Amount of thermal Energy Developed by the ARC and the Very High Frequency of
The Arc. Perhaps One Think of An Arcing Fault as an Embryonic Electrical Circuit Defect,
unlike the default that has fully developed and matured into an adult electrical fault
Such as a bolted fault. Experience shows that on occasion a short circuit will clean
Before, or during the operation of the OCPD. That is, it will develop into an open circuit.
Bolted faults
OCCASIONALLY A Short Circuit Will Evolve That Has Such A
FIRM Connection (To Either A Group,
said to be a bolted fault. We are saying that it was not a loose connection, it was not
wiggling around.
an arce type fault.
A loose connection type of fault May Produce Enough Heat to
Melt or Plasticize the Conductor S Conductive Material and Cool Enough to the Produce
a joint so firm and secure as to be comparable to a welded job. Then we will call it
a bolted fault. Circuit breakers are typically calibified to be capable of responding
To a Bolted Type Fault. This is Because A Bolted Type Fault Produces Sufficient Current
Flow to Cauther The Thermal (after Intent Delay) or The Magnetic (Non-Dlay,
But only if sufficient Current Flow is Produced) Trip Elements to open the circuit.
SafeTy First, Always First
The Exact Nature of Electricity- that it cannot be detected
With the eyes, ears, or the nose, yet if it is touch, it can kill- Must be remembred
at all times. Circuit breakers are very reliable components of an electrical system; however,
They are man making and are subject to becoming default. Proper Lock-Out-Out Procedures
Must be followed when working on electrical circuits Above 50 Volts. Personnel Protective
EQUIPMENT MST Be in Serviceable Condition and Properly Worn. Safety is a requirement,
Not an option, of everything electrical task, large or small
Nature. Always use the three-therep method when checking for voltage.
Take good care of your electrical test meters, having them
Checked at Least Every Years for Insulation Streangth and for Calibration as Listed
In the Instruction Booklet, or ONCE A Year Otherwise. While A Switch May Visually Indicate
That the controls have open, a meter must be used to confirm that no voltage remains
in the equipment to be worked on. Many Times More than the public of power is provided
To a Machine. Some Electrical Circuits Contain Motor Starting/Running or Power Factor
Correction Capacitors that May Still Be Chargen after Power Has Been Removed from FROM
The circuit.
When working with other do not assume that they know how
Operating your meter, and do not assume that you know how to operate the meter. Take the
Time Necessary to Learn How to Properly operate the tests that you will be
Required to use.
Something, But BEING FOUND Dead on the job I Believe to be Permanently Embarrassing. If
You would like to leave more about the use of multi-meters and such, I suggest that you
See If you can get your hands on a copy of the book titled test equipment,
published by delmar, isbn: 0-8273-4923-8.
NEC Requirements for Circuit Breakers
The National Electrical Code has several requirements for city
Breakers (OverCurren Protective Devices).
Others can be found in the various specification articles, such as 430 covering motors.
? Main, Feeder, and Branch Circuit Breakers Must Be Installed in A Readily Accessible
location.
? A Working Space Must be as wide as the equipment, or at Least 30 INCHES WIDE and Three
Feet Deep, or Deep Enough to Allow ANY Doors to be Opened at a 90 Degree Angle in Front
of the equipment housing a breaker.
? When the operating handle is in the up positive ites centerline be not more than 6 ft.
7 inches about the floor or working platform.
IT Mustalled so that it is secure on its mounting summer.
? When installed the up position must be on and when the operating handle is moved double
This must be the off posity.
? The breaker must be clear Marked as to my office and on positys.
? The breaker must be clear market, such that after installation the amperage rate
is clearly visible. (There are some exceptions see 240.83)
? The Operating Handle Must be of a trip free design, so that it cannot be blocked or
Kept from Tripping Due to Some Type of Obstruction Keeping the Operating Handle from Moving
to the tripped position.
? When wires are connected to a breaker they must be properly torqued to the breaker s
Termination points.
? The NEC Has Specific Requirements for Both Afc and GFCI Type Circuit Protectors that
Are Mostly Applicable Based UPON Specific Locations.
There are spiecific product type requirements for city breakrs
To be lived by a nationally recography.
Be caping in this short paper. That Means Detailed Informaion Relating to Engineering
Type Testing and Things that the Circuit Breaker ManuFacture Must Know About Are Not Covered.
This is not an everything you ever wanted to know about circuit breakers
Type Article.
In the next part of this article the following topics will
be covered.
Functions
Types
Components
VOLTAGE RATINGS
Ampere rates
Ampere interuptingurrent (AIC)
Testing -listing of Circuit Breakers
Not all breakers are rated the aame
The Electrical ARC
Effects of Current Flow
Thermal Energy
Thermal trip element
Magnetic Trip Elements
Hydraulic-Magnetic Trip Elements
If you have any questions or comments, please send me an e-mail.
Remember Work Smarter, Not Harder
L. W. Brittian
Mechanical-Electrical Instructor
lwbrittian@hot1.net
Electrical Circuit Breakers
Part 2
In this the second part of the article covering circuit breakers,
The following topics are cover:
Functions
Types
Components
VOLTAGE RATINGS
Ampere rates
Ampere interupting capacity (AIC)
Testing-Listing of Circuit Breakers
Not all breakers are rated the aame
The Electrical ARC
Effects of Current Flow
Thermal Energy
Thermal trip element
Magnetic Trip Element
Hydraulic-Magnetic Trip Elements
Circuit Breaker Functions
Later in this article we will cover several more specification features
Of some spiecilized types of circuit breakers, but for now let us begin by saying that
a Circuit Breaker S Main Functions Are:
? Sense The Current Flowing in the Circuit
? Mease thecurrent flowing in the circuit
? Compaare the measured care to its pre-set trip point
? Act within a Predetermined Time Period by Opening The Circuit as Quickly as Posses
To Limit the amount of Energy that is allowed to flow after the trip point has reached.
In a condense manner, we can say that a circuit breaker function
To Prive OverCurrential Protection, and Isolation from Energized and Un-Ergized Circuit
Components. As Safety Devices, These Functions Must Be Performed, Without Failure, Without
DAMAGE to the Protected Circuit s Components, from nocurrent Through the Breaker S
Rated ampere interupting capacity (AIC). Now that is a big job and an imageant job.
Modern Breakers Routinely Do their job day in and day out with
very little maIntennce.
They Do Fail. Hopefully this paper will help you to better under the appreciation the
Task Performed by Those Little Black Boxes.
Circuit Breaker Types
Medimum and Low Voltage Circuit Breakers are Commonly SEPARATED
INTO The FOLLOWING Group Based Upon the Type of Material used to make the frames or cases:
MOLDED CASE, (MCCB) The Most Common Low Voltage Type
Insult Case, (ICCB) The Internet Voltage and amperage
sizes
Metal Clad, The Higher in Voltage (MEDIUM) and amperage
rating
Circuit Breaker Components
The Five Basic Components of a Circuit Breaker Are:
Frame or Case Made of Metal or Some Type of Electrical
insultation
Electrical Contorys
Arc EXTINGUISHING Assembly
Operating mechanism
Trip unit, containing either a thermal element, a magnetic
Element or Both
Circuit Breaker Voltage Ratings
Low Voltage (Under 600 Volts) Circuit Breakers are Commly
Rated for, 120 Volts, 240 Volt, 277 or 480 Volts AC. Some Breakers Are Rated for Used
In dc Circuits, WHILE OTHERS are rated for use in Either Ac or DC Circuits.
Single Pole Circuit Breakers Are Rated for a Voltage Potential
Between The One Hot Wire and A GroupDed Surface. Breakers that are intended to be part
of A Two or Three Pese Circuit Are Rated for a Voltage Potential from OPPOSITE POTENTIAL,
To OPPOSITE POTENTIAL, or Phase-to-PHASE. You must not use two Single Pole 240 Volt Breakers
To Control a 480 VOLT CIRCUIT, But Two Single Pole Breakers Rated 277 VOLTS COULD Be USED
To Control a 240 VOLT CIRCUIT.
When impheperly applied outSide of its rating, a breaker may
Not be avle to exceeish the arc when attempting to clear a fault. Some breakers have
What is Called a Slash (/) Rating Such as 120/240 or 277/480. Breakers that are slash
Rated Should Not Be used on Un-GRounded Systems, as they has not ben tested for saving
Operation on the time of systems.
Mr. Holt S ARTICLE UNDERSTANDING CIRCUIT BREAKER MARKINGS, in the November
2001 Issue of EC & M Magazine. Cooper-Bussmann ALSO HAS An Article Covering Slash Rated
Circuit breakers, if you would like to read strong more more.
Circuit Breaker Ampere Ratings
Circuit Breakers Have An Ampere Rating (Typically Marked on
The end of the operating handle).
can carry with exceeding its rate. As a general rule the city breaker s ampere
Rating Should be the Same as the Conductor S AMPACITY. In Other Words We Would Not
WANT to PUT A 60 AMP BREAKER on A 10 AMP Wire. Breakers are tested in Open Air, with a
Temperature of some 40 or 50 Degrees C.
When a breaker is placed within an enclosure, cooling airflow
Is RESTRICTED; This Reduces the Ability of the Breaker to Carry A Current to 80% of ITS
Ampere rating. When they are installed in an electrical enclosure, breakers will try trip
When aurrent in the amount of their rating is placed upon them controlsly. Breakers
are designed to be able to safly carry a current in excess of their rating for very very much
Short Periods of Time to Allow Some Types of Electrical Equipment (Called Inductive Loads)
Such as motors to start up.
While Not as Common, some breakers are rated for 100% Continuous
Loads. These are typically Called Supplementary Protectors (SP) and Not Circuit Breakers.
Ampere interupting capacity (AIC)
Circuit Breakers Are Tested and then Rated as to their Ability
To Open The Protected Circuit with A Specific Amount of Current Flowing in the Circuit.
Circuit Breakers Typically Have AIC Ratings of Between 5,000 and 200,000 AIC. The Amount
of Fault Current available must not exceed the breaker s Abily Open The
Circuit. Not only must the breaker be rated for the applied voltage, and Continuous AMPERAGE
load; It Must Also Have An AIC RATING EQUAL to Or Greater than the Available Current AT
The local
So that the available fault curren exceeds ites aic rate may blow up, just like a bomb
Would Explode Were it to Attempt to Clear a Fault Current ABove its Rating. When opening
A faultd circuit, it is posesible for smoke and fire to be exhausted from a breaker. If
You would like to see a breaker belch fire and smoke, see if you can local and view the
Cooper-Bussmann Fime Company Video Titled Specification Grade Protection.
The Visual Impact of this time lively enhance your application of the imagence
Of an Electrical device s aic rate far, far better than any words of mine.
In your Safety Classes, You Likely Have Received Training in
The step to the size routine before Manually Switching Electrical Circuits, and this videotape
Will reinforce the value of this easy saftedy step. This is also a good reason why sheet
METAL COVERS CALLED DEAD Front Trim Should Be Re-Installed on LoadCenters, Panelboards, Panelboards
and the like before operating switching devices.
Electrical Engineers Tell us that the two Major Factors that
Govern the amount of fault more can be delivers in a system are the kva rating
of the transformer and the image of the transformer.
Motors in the Circuit Also Adds to the Amount of Potential Fault Current. Considering
480 Volt Systems, Combined Transformer and Motor Fault Currents Can Range from 14,400
AMPS for a 500 KVA Transformer with An Impedance of 5.0% to SOME 90,000 AMPS for A 3500
KVA Transformer with 5.75% Impedance. Selecting all circuit breakers for Higher AIC RATINGS
May be the saffety first and count last method.
An Engineering Level Study of a Facility S Electrical
System Every Five Years (or BeFore Plant Remodeling is Undertaken) is a good IDEA. The
Study Should INCLUDE A Review of the AIC of the Plant s Breakers and the Fault Current
That the Plant S Electrical Circuits Can Deliver to the Line Terminals of All Major
circuit breakers (OCPD).
Testing-Listing of Circuit Breakers
MOLDED CASE LOW VOLTAGE CIRCUIT BREAKERS Are Typically Tested
To ul Standard 489. Ul uses the footowing test Goals to determine if a breaker is consider
to be saving (IncomPliance with their Safety Standard):
? The breaker must interrupt the maximum short circuit curren two times.
? The Breaker Must Protect itset and the Connect Conductor and the Equipment It is
Installed in.
? After having ben testd the breaker must be fully functional and pass a thermal calling
TRIP TEST AT 250% of ITS RATED AMPACITY; and Pass A DIELECTRICTRIC WITHSTAND TEST AT TWO TIMES
ITS Rated Voltage or A Minimum of 900 Volts.
? The Tested Breaker Must Also Operate Properly and Have Continuity in All of its POLES.
UL-489 Listed Circuit Breakers Are Tested with a Four-FOOT
LENGTH of Wire, as they must perform during the test as they will be installed in the
Real world, so wire is connected to make the test a bit more realistic. During the test
The Conductor s Insulation Must Not Be Damaged. The Connect Wires Must Not Be Pulled
Loose from the Breaker-Conductor Termination Lug. The Breaker Case Must Not Be Damaged
AS A Result of Cable Whip Forces (CAUSED by the Potentially Huge Amount of Magnetic Force
DEVELOPED Under Short Circuit Conditions).
Heat Sink for the Breaker. That is, it helps to disipate heat product with the breaker.
This is becaude the breaker s cases as not only an electrical but a thermal insulation
Also, in that it tends to Retard the rate of heat transfer.
have wire size ranges marked on them. TOO Small a Wire Attached to the Breaker Cannit
Adequately Aid in Cooling the Breaker.
The Temperature at the Circuit Breaker S Terminals Must
Not Rise More than 50 Degrees C. Above the Ambient Air Tempeature Surrowing The Breaker.
The ul-489 test standard has ben used to test many, many circuit breakers over the year
And has proven to be a pretty good standard by which the safety of circuit breakers can
be determine.
If you would like information
Circuit Breakers (IEC-947-2), I Suggest That You Read Cashnique # 150. Be Prepaired
for a good bit of concentration; this document is written at the engineering level.
Good Folks with Square D Can Help You Locate It on their Web Site.
Not all breakers are rated the aame
A Circuit Breaker L itd to UL-489 Standard is not the ate
Animal as a breaker-looking thing,
Protector (SP).
Fault Current Conditions and is Tested to a Higher Degree to do more
Protector (Commly Tested to ul-1077 Safety Standards).
Supplementary Protectors cannot be used as service equipment
Without there is device such as ul-498 Listed Breaker or Fuse in the Circuit
UP-Stream of Three, as they or may not open the circuit under short circuit conditions.
It may be different to determine the difference between a city breaker and a supportmentary
Protector by Simply looking at anstalled device.
Out that we need to pay close attentation to what we are working with, as the testing processures
and listing requirements, among all of the look-a-like black boxes.
I would that I could pass aME SURE Just looking at
IT (without using a book or removing the device) Method of Determing if it was a circuit
Breaker, or a supportmentary propector, but at this this moment regrettably i am unable to do
so.
The ate is somewhat true of magnetic trip only (Short Circuit
Protection) Motor Circuit Protectors (MCP). With MCP S it Helps that an amperage
Rating is not imported on the end of the operator handle. However that aid is of limited
Value, as the NEC Allows The Marking to Be Hidden by Type of Covering Trim When A
Circuit breaker is rated over 100 amps.
Supplementary Protectors are not required to have an aic marked on them, but neither are
Circuit breakers that have an aic of 5,000 amps. If you are a bit confused, so am i; and
Try as best they can, ul has not ben able to communicate to me a hard and fast rule of
How I can Physically Tell the Difference in the Field with excementing the device, OR
Finding Part Numbers and Looking Them Up in A PARTS BOOK (that Plant Maintenance Folks
Do not typically have readily accessible).
The Listing of Supplementary Protectors by Review A Copy of Ul S Listing Guide
number qvnu2 and circuit breakers number divq.
The Electrical ARC
As a Two Energied Electrical Contracts Sepata, One
CONTACT (Called the Cathode) Transmits Electrons and the Other (Called the ANode) Receivers
THEM, that is an electrical arc is created. if you we to ask a layman to tell you what
Electricity looks like, he would likely describe an electrical arc, white it is not. We. We. We. We. We. We. We.
Frequently See a Wide Range of Arcs (The Godzilla of Electrical Arcs), The Lightningings
Strike, And the Micron Sized Static Electrical Discharge Occasionally Experienced afterer
Walking across a carpeted floor.
The Electrical Arc is a naturly occurring eve of a part of
Doing Business with Electricity so to speak. The Visible Arc (IONIZED Air) is not electricity
But an effect of electricity, just as heating of consorters wherent flows in a circuit.
An Electrical Arc Produces An Intense Amount of Heat That Can Reach Temperatures of 4,000
C and Higher. If not exclusively, an arc can pit (a transfer of metal from one
Surface to Another) Or event Destroy The Electrical Contracts and Insulating Material Such
as the breaker s casing.
Circuit breakers are designed to minimize, if not eliminate,
DAMAGE CAUSED by Electrical Arcs in the Following Ways:
Submerge the controls in oil
Place the contacts in a vacuum tight enclosure
Immerse the controls with an ins such as SF-6
DIVERT The Arc Away from the main contalts to seacondary
Contacts or Arc Horns
DIVERT The Arc Away from the Contage with A Magnetic
Field (Blowout Coils)
DEFLECT The ARC Off OF the Contacts by USE of a Differential
pressure
Extinguish the arc in Arc Chutes
Make and searted the contarts at high speed
Low and Medium Voltage Circuit Breaker Manufactures Have Use
Combinations of the Above Methods. Methods Such as Oil, Vacuum, and Games are Less Common
On modeln low and medium voltage breakers.
While it is correct to say that when the anc sine wave reaches
The Zero Voltage Points, The Arc Will Go Out Due to the Lack of Voltage, this is not the
Entire picture, for arcs are more complicated. Quickly state, the arc has a voltage
of its own, and if the air between the contacts is not
Gap is not wide enough, The Arc May Re-bstablish itset when the support,
Again increases.
A Common Method USEd in the Above 200 Amp or so size breaker
is the user of Arc Extinguishing Chutes. This Method Diverts and Sections Individual Sections
of the Arc Away from the Contacts Into Thermally and Electrical ConDuctive Chutes WHERE
The Arc is Stretched and COOLED SUFFICIENTLY to Extinguish it. The user of contactally
Coating Material Such as Silver is used to Harden Contract Surfaces and Reduce Pitch
Damage. Spring Powered Switching Contracts are designed to increase contact mode
To Reduce the Life of an Arc.
While Many Electrical Circuits are wired use Copper Conductors,
Copper-Only Contorys are not user
The Contract S Impedance, Which in Turn Increases the Amount of Heat Generated.
An Arc Can Travel Across Some Types of Insulated Surfaces Thats
have ben heated so hot as
PATH for Future Curren Flow. This Means that External Breaker Insulation Materials Should
be inspect from time to time for indications of overheating, dust, and for the public
Formation of a Fine Carbon-Like MateriL that can result in a short city.
If you would like to read more about the electrical Arc at
An Engineers Reading Level, then Cahier Technique # 154 is a good article. It can be double
Loaded for free from the web. The good folks with square d can help you locate it on their
Web site.
The effects ofurrent flow
When Current Flows in A Circuit Two Effects Are Produced, Magnetic
and thatmal.
a magnetic force. For exmple, under dercuit Current Conditions, The Magnetic FORCES
Build up very quickly. Just as a magnetic can be used to move a metal object, so can magnetic
Forces Torque or Stress Circuit Components.
Under Severe Short Circuit Current Conditions Busbars Have
Been Instantly Ripped from their Mountains, and Large Cables Have Been Whipped
as to have ben pulled loose from their terminations.
Energy Was Melting Sand in Fuses Into Glass, Steel and Copper Metals Weee Being Heated Heated Heated Heated Heated Heated Heated
So hot as to be turned into a superheated gas (solid metal before a liquid, and then a
Vapor). These event CCCURRED Within the TOOK the OCPD to Open the faultd circuit.
Circuit Breakers Routinely Open Shorted Circuits in Something Like 3/60 to 5/60 of One
sex.
We May TEND OCCASIONALLY to Focus Our attentation on the Electrical
Insging aspects, While Potentially Forgetting Magnetic and Thermal Effects Under Short
Circuit Current Current Current. The Practice of Security Big Cables in Place So that they
Stay in Place Under Short Circuit Current Conditions with Thin Plastic Like Twine Should
be reconSideRed. So too shop
used of a torque wrench.
Thermal Energy
Excessive Current Flowing in a Circuit Can Result in Heat Relate
DAMAGE to Electrical Equipment. That is Because a Rise in Currentes in An Increase
In thermal Energy. Mathematical Speaking, A Current Increase Results in a Squared Value
Increase in the amount of heat, that is, I squared t means that the higher they the current
The Much Greater the Amount of Heat that will be deverted.
That An Increase of Only Twenty Degrees C. Above the Maximum Rated Tempeature of An Electrical
Insulator (Motor Windings) Can Reduce its Life by AS Much as 50%. Electrical Insulation
Can withstand only a limited amount of repeated overheating
Stress cycles are cumulative) Before it fails.
Thermal trip element
When the circuit is required to be provided with a propective
DEVICE for Overload Type Conditions, a thermal time delay element is typically provided.
The thermal element provides a time delay function, that is to say, as, as, asn
The Current Flow in the Circuit Increases, Heat Begins to Builds Up in A BI-METAL ELEMENT
(That is Made from Two Thin Strips of Different Metal) and It Begins to Bow and Cautal
the controls of the breaker to open. These two metals are selectd for their different
Rates of thermal Expansion (Heating) and Contraction (Cooling). Having Been Fused Together
by the manual, Changes in their Tempeature Results in them Expanding and Contracting
In an arc, and not in a straight line. This movement all to be used as the source
of the force needed to open the breaker s contacts.
Thermal Elements Require Some of the Heat to Be DISSIPATED
BeFore they can be reset after having tripped. This Means that when a breaker trips on
Thermal Element (Due to a Running Overload) It May NEED A Few Minutes to Cool Office
it can be reset.
Magnetic Trip Element
The trip unit is the brain of the breaker. It consists of the
Components needry to automatically open the circuit when an overcurrent is ased.
General A Magnetic Sensing Element or Both A Magnetic and a Thermal Sensing Element
Will be included in the trip unit.
When a breaker has only a magnetic saing element, it is a
Non-Delay Instantaneous Trip Type. With this type of circuit breaker, no delay has ben
Intentally design in ITS Operation.
a moveable plunter, white is held in place by a spring.
The Magnetic Coil and When IT PRODUCES A PULL On the Plunger Greater than the Retaining
Spring, it will move the plunter, which results in the device s contacts opening.
When an OCPD HAS only a Magnetic Sensing Element it will provide
Protection only from short,
The the types of devices are Called Motor Circuit Protector (MCP).
DEVICE Such as a Three Phase Motor Starter with Thermal Overload Relay-Heater Elements
Proves running overload propaction.
When a circuit breaker has tripped on the magnetic element,
It can be ImmediaTelly Reset. One Should Not Reset A Breaker More than Twice with Correcting
The Cauise of the Fault. To do so May Result in Serious Personal injury.
Hydraulic-Magnetic Trip Elements
SOME Brands of Circuit Breakers Use a Hydraulic Fluid (Silicone)
Type of Current Sense Element. With this type of sarsor, a wire is coiled around ang an
OIL FILLED CYLINDER CONTAINING A PISTON, Which is connected on one end to the breaker s
TRIP Unit. This forms a magnetic coil through low whiteurrent flows. The piston is
Held in a posity by a spring. When Current Flows in the Coil, A Magnetic Field is Created
That publics the piston deeper and deeper into the coil. As they current in the city increases,
So does the coil s magnetic filed stringth; the spring is compressed, drawing the
Piston Deeper Into the Coil, increasing the coil s magnetic file
Movement Progresses, The Fluid Tends to Oppose Rapid Movement of the Piston in the Cylinder.
By Varying The Fluid S Viscosity the ManuoFacture Can Alter
The amount of force that retards the piston s movement; this in turn allows the amount
of time delay to be varied. by Changing the size of the coil wire and number of wraps
of the Wire in the COIL, The amount of force (mmf) created by the magnetic filed can be be
Changed (Changing Either or Both the Quantity of Amps, or the Number of Turns of the Wire
CHANGES the amount of public product by a electro-mailc coil).
ManuFactures using this type of element design can offer the
Protection of A Quick Responding Magnetic Element and the Time Delay of a Frame Circuit Breaker Fixed Switch ODM ManuFacturer thermal Element
In their breakers without using a bi-metal element.
In the next part of this article the footowing topics will be reviewed:
Methods of mounting circuit breakers
FIXED MOUNTED CIRCUIT BREAKERS
Removable Moundted Circuit Breakers
Drawout mounted circuit breakers
Methods of Securing Circuit Breakers
Stab Lock Type Circuit Breakers
Bolted Type Circuit Breakers
DIN RAIL MOUNTED CIRCUIT BREAKERS
If you have any questions or comments, please send me an e-mail.
Remember Work Smarter, Not Harder
L. W. Brittian
Mechanical-Electrical Instructor
lwbrittian@hot1.net
Electrical Circuit Breakers
Part 3
In this the third part of the article covering circuit breakers,
The following topics are cover:
Methods of mounting circuit breakers
FIXED MOUNTED CIRCUIT BREAKERS
Removable Moundted Circuit Breakers
Drawout mounted circuit breakers
Methods of Securing Circuit Breakers
Stab Lock Type Circuit Breakers
Bolted Type Circuit Breakers
DIN RAIL MOUNTED CIRCUIT BREAKERS
Methods of mounting circuit breakers
For our study pulposes we will divide the method use to mount
Circuit Breakers Into Three General Groups: Fixed, Removable, and Drawout. A Review of
These mounting method follows.
FIXED MOUNTED CIRCUIT BREAKERS
A Circuit Breaker that is bolted in its enclosure and wired
To the load frame, is called call a fixed mounted circuit breaker.
Rated 600 VOLTS or Less and Are Front Mountain. Power is provided to the breaker typically
by Wires or Sectional Type Busbars. Power Feeding The Circuit Breaker must be turn
In Order to Physical Remove the Fixed Mountain Breaker.
Removable Moundted Circuit Breakers
A removable circuit breaker has two parts, a base, which is
BOLTED to and Wired to the Frame, and the actual breaker, Which Has Insulated Parts that
ElectricLly Mate with the base. This means of mounting all not to be rePlace
With out RE-WIIRING The Unit on the Line Side of the Breaker. This type of mounting is
Typically use for breakers rated 600 volts or less.
Drawout mounted circuit breakers
A drawout circuit breaker also has two parts, the base, which
Is Bolted and Wired to the Frame and the Actual Breaker, Which Slides into and Electrically
Mates with the base. This allows the unit to be replaced with having to turn off the
Power Feeding The Breaker.
Unit.
AS A Safety Feature the Units Are Interlocked to Automatically
Turn the Power Off Just Before Removal of the Breaker Begins. by Design, only the circuit
Breaker s load must be turned off to remove the breaker. This method of mounting
Allows for a single breaker to be disconnected from the power support. That is to say that
It Does Not Require That All of the Power Be Disconnect from All of the Breakers Installed
In the larger enclosure such as a motor control center.
There are various designs userd to facility the racking-in (Installation)
And Racking Out (withdrawal) of the Drawout Type Circuit Breakers. Some Utilize
SOME FORM of Jacking Scream to Initially Move and Thus Electrically Disengage The Breaker,
Then a traveling trolley type of house
Breaker During Removal and Re-Installation.
as the large (Physical Size) Breakers are too heavy and too bulky to be safly moved
Into and out of positive by one person.
Methods of Securing Circuit Breakers
Circuit Breakers are typically secured in Place by One of the
follow methods:
Through bolts
Stab Locked to the Busbar Or Some Type of Receptacle Connection
Bolted to the busbar
Din rail mountted
Stab-Lock Type Breakers
This method of circuit breaker mounting utilizes a male-female
Type of Plug and Receptal Connection to A Metal Busbar on One End. The opposite end
of the breaker is mated to the enclosure house
With the busbar and is not part of the electrical circuit. These types of breakers are
Found in Home and Light Commercial Applications Installed in LoadCenters. With This Method
of MOUNTING, SOME MOVEMENT of The Circuit Breaker Case Is Normal.
Breaker Case Movement is Typically 1/8 of An Inch or Less on the Busbar End. Single Pole
Breakers tend to exce its aMONT of Movement Due to their Greater Aspect (Width
to height) Ratio. The Circuit Conductor Termination Lug May (But Not Necessarily) Also
exhibit some minor movement of the terminal lug; Again this movement is less than about
1/8 of an ins.
On Occasion The Line Connection (S) May Lose Some Gripping Force
Overtime; When this Occurs One May Be Tempted to Re-Pinch The Connection Closed Just A
Bit. This pingsching should be avoided, as repeated bending results in the metal losing
Its stringth. When a loose connection has become evidence, the breaker should be replaced.
The Busbar and ITS Insult Should Also Be INSPECTED for Indications of Overheating
Related Damage. With This Mountain Method, VOLTAGE DROP TES
OR Panelboard S Main Lugs to the Breaker S Load Terminal (s).
Bolted Type Breakers
When a Longer Service Life Breaker is WANTED, a Bolted Type
is typically used. The Types have a metal tab (One for Each Phase) Sticking Out from
One End that is bolted to the busbar with a Machine Scream (Bolt Type Fine Threads and
Not Sheet Metal Screw Type Steep Pitch Threads.
The Retaining Bolts Or Machine Screws Will Have Power on theMless Power to the Entire
Panelboard has ben removed.
It is not uncommon for some indictants to determine that it it
Is NiceSARY to Replace the Types of Breakers with Power Still Applied to the Busbars.
I am not a big fan of working any thing
Good Folks get huing what was initially anticipated as being a quick and simply task.
When this type of breaker must be replaced with power still application to the busbars, it
Should be do done only under strict safety procedures; using proper personnel protuctive
EQUIPMENT and DOUBLE INSULED Tools (Everyday Plastic Handle Scream Must Not Bele
use).
On more than all ocasion I have with
Rehearsals of this type of activity severty tables unable eACH SAFETY STEP WAS DORRECTLY.
Take the time you need to be saf.
DIN Rail Mounted Breakers
With this method, a mounting rail is secured to the enclosure
And the breaker is snapped onto the mounting rail. This allows replacement to be do
Quickly as the device can be unclipped and a new one clipped on to the din rail. ConDuctors
for the support and load are typically secured to the breaker users
that are tightned by some type of Threaded FASTENER. While Not as Easy to Replace as
a start
Panel Building and Individual Breaker Replacement Later on.
The letters din stand for German Industry Standards. Din Rails
Are available in more than one physical size. The din rail mounting method is increasingly
Replastic Thru-Bolt, Foot, and Plate Mountain Methods once More Commonly used.
In the next part of this article the following topics will
be covered:
Time Current Curves
Available fault current
Series rated devices
Selective Coordination
Line and load terminal connection
Ambient Compensated Circuit Breakers
If you have any questions or comments, please send me an e-mail.
Remember Work Smarter, Not Harder
L. W. Brittian
Mechanical-Electrical
Instructor
lwbrittian@hot1.net
Electrical Circuit Breakers
Part 4
In this the fours part of the article couple
The following topics are cover:
Time Current Curves
Available fault current
Series rated devices
Selective Coordination
Line and load terminal connection
Ambient Compensated Circuit Breakers
Time Current Curves
The Proper Design of An Electrical System Involves Many Detailed
Tasks, Such As Selection of the Circuit Breakers that Will Protect the Conductors, Equipment,
And people who operate the equipment. Proper selection and coordination of breakers for
a special system is facilitiveted by the user of time current curves. Reading the Curves
is quite technical and will not be capriced in adequate depual to allow someone to properly.
Select OCPD S; My Intention in this Short Paper is to provide a brief overview only.
Time Current Curves Are Plots of the Amount of Current (Vertical
Scale) Flowing in the Circuit to the Time (Horizontal Scale) Required for the Breaker
to clear the fault.
Ultra-short, short, medium, and long.
Melting (Eutectic Alloy) Element Type Electrical Fuses Have
No moving parts, so no inrtial forces need to be overcom for the fuse to open the circuit.
Breakers, on the Other Hand, have parts that must be moved from one position
to open the circuit. General’s speaking, farticularly curren limiting fans)
Open A Circuit Faster than Circuit Breakers. SOME SOLID-State Components can be damaged
Beyond Repair in Less Time than a Circuit Breaker May Be Able to Open The Circuit. For.
This and Other Reason, Fuses and Not Electrical-MEChanical Circuit Breakers Best Protect
SOME TYPES of Electrical Components. RESTATED, You Cannot Always Replace a Fuse with A
Circuit breaker of the same voltage and amperage value.
The time an overcurrential protrise device operates can be divled
Into The Following Four Segments. Sensing Time: Magnetic Elements are quicker than thatmal
Elements (Which Intionally Add Delay).
as they have no parts to move. Arcing time: The time during which an arc is present both
FUSES and BREAKERS HAVE to Extinguish The Resultant Arc. And Finally Arc Extinguishing
Time: The time the propective device takes to exceeduish the fault s arc varies with
The Type of Device, Amperage Rating, AIC RATING, VOLTAGE, and the Amount of Short Circuit
or overloaded due.
Available fault current
When selecting circuit breakers it is important to know both
the maximum Continuous amperage and the available fault (Short Circuit) Current. The NEC
in Article 110.9 Proves the Following Guidance, Equipment Intended to Interupt
Current at fault levels, shall have an interrupting rating support for the nominal
Circuit Voltage and the Current that is available at the line terminals of the equipment.
There are two method commonly used to comply with this ne code requirement.
The Most Conservative Method is to select all ocpd s based
upon the fault current available at the electrical service (or source of support). For
EXAMPLE IF 50,000 A.
Even The Most Distant (from the Service) Branch Circuit Breaker Should Be Selected to
have the Ability to Safly Open The Circuit with 50,000 AMPS of Fault Current, Even Thought
That amount ofurrent would not be available to the line terminals of the most distant
Circuit Protective Device. Depending Upon the Specific Nature (SUCH As Arcing, or Bolted)
of the fault, the topal amount of fault current available may or may or may not be deverted
During Operation of the Next Upstream Protective Device.
Series rated devices
The Second Method of Breaker Selection, Which is more realistic
and more first Cost Economical, is to select the device (s) Based upon the level of fault
Current That Engineering Level Calculations Determine Can Be Potentially Available AT
The device’s line terminals.
ONE MAY Question Why Spend the Extra Money Purchasing Breakers
That have aic more than the system can deliver? When it is reasonable to anticipate
That the Power Supply S Capacity Will Be Increased, The Initially More Costly Selection
May be justified Based upon anticipated system capacity growth.
Selective Coordination
Selective coordination is the select and application of
Circuit Protective DeviceS in Series Such that Under Overload or Fault Current Conditions,
only the device just up stream from the overload or fault will open to clean.
The remainer of the circuit s profile devices will remain closed passing power
To their Individual Loads. SELECTIVITITY can be base upon time orcrent levels. This. This. This. This.
Method of Selection Alows Two Devices to be Connected in Series with Each Other, And
Seeing the same level to respond in different times, the one closest to the fault
With the shortest weway will open the circuit.
While having the saving level trip point, would have a longer trip delay time, allowing
The Closer Device to React FIRST to Open The Protected Circuit.
If not properly coordinated, the device closest to the fault
Could the Longer Time of Response (Both Haveing The Same Current level Trip Values),
And the next propired device up stream of the city, Resulting in a Potentially
More Wide Spread Circuit Outage to Be Experienced by the Facility. When the breaker nearest
The Circuit S faces not trip the one above it does, a review of
The degree of coordination should be underrtaken.
Line and load terminal connection
The terminals at the top of a breaker (when installed in A
Vertical Position) Are for for the Source of Supply and Are Called the Line
Connections (Nema Markings L-1, L-2, L-3, or IEC Markings 11, 21,31). The terminals at
or IEC Markings 12, 22, 32).
connecting to the touch.
Some breakers are listted such that they may be connected to
the source of support either at the top (line) or the bottom (load). These breakers can
then be used in a back-fed type of application; that is power can be connected to the
bottom (load) of the breaker and the breaker can be used to support
;
in that manner only. That is like to the source of power and load terminal
To the Utilization Equipment. The NEC Requires That Back-Fed Type Breakers Be So Installed
That it takes more than a port the breaker to remove it. See article 408.16 (f) of
The 2002 edition.
Ambient Compensated Circuit Breakers
There are some compommon install,
to be propied with the local
CONDITIONS, Particularly Ambient Temperant.
where a fan motor is located in a minus 40 Degree Ice Cream Freezer and ITS Protector
Circuit Breaker is Located in a Poorly Ventilated Motor Control Center Room where the
AIR TEMPARATURATURE RPINELY Exceeds 100 Degrees F. During Hot Summer Months. This Could
Result in The Breaker S thermal Element Trip Point Being Reduced Due to ITS Hotter
ambient. The breaker cored experience nuisance tripping.
To Avoid Temperature Related Offsets Breakers Are Available
with an ambient compensation feature. This design enhancement feature allows the breaker
To Open The Circuit, With Out Deviation Caused by Changes in The Ambient AIR TEMPERAN
Within a listted ambient testure range.
In the next part of this article the following topics will
be covered:
Insult case circuit breakers
Accessories
Shunt trip
Auxiliary-Remote Alarm Switch
Group fault sensor
Under Voltage Trip
Lock-out-tag-out process
Remote Operator Handle
Stored Energy Breaker Operator
If you have any questions or comments, please send me an e-mail.
Remember Work Smarter, Not Harder
L. W. Brittian
Mechanical-Electrical
Instructor
lwbrittian@hot1.net
Electrical Circuit Breakers
Part 5
In this the fateh part of the article covering circuit breakers,
The following topics are cover:
Insult case circuit breakers
Accessories
Shunt trip
Auxiliary-Remote Alarm Switch
Group fault sensor
Under Voltage Trip
Lock-OUT/TAG-OET PROVISIONS
Remote Operator Handle
Stored Energy Breaker Operator
Insulated Circuit Breakers (ICCB)
This type of circuit breaker is assembled on a metal frame
contained within an insulated case and is provided with Air Break Contory.
of Circuit Breakers are used as a part of Larger Installate
MCC Type Switchgear.
The Insulated Case Circuit Breaker Typically Has A High Short
Time withstand and high interrupting rating. They are available Today with both a local
And a remote means of committing for setting of the various value, and facilities
Such Tasks As Remote Monitoring of Electrical Energy Consumption and Troubleshooting.
The Insult Case Circuit Breaker Can Be Purchaset with Any of A Growing List of
Accessories, Several of Which are briefly reviewed in the follow paragraphs.
Accessories
The follow is a briefing society of the acceptable
Commonly available for the ICCB and for MicroComPuter-Equipped Circuit Breakers Today.
ONLY Those Specific Accessories Listed for A Specific Breaker Should be attached to a
Breaker. To do Other Wise May Potentially Compromise Safety.
Shunt trip
SOME TIMES It is Advantageous to Turn a Breaker Off FROM A
Remote Location. TO FACILITETE THIS TASK, An Accessory Called A Shunt Trip Feature Is
Installed by the ManuFacture Inside of the Breaker. This Device Consist of An Electro-Magnetic
Trip coil that is connected in server an external fired witch. When the switch
Contracts are Closed, Power is passed to the shunt trip coil causion the breaker s
Mechanical Latch to Move to the Open Position. Re-closing the breaker is not by physically
Going to the Breaker and Manually Moving the Operation Handle to the On-CLOSED POSITION.
When Opened By Use of the Shunt Trip Coil, The Breaker S
operating handle moves to the off
FULL HANDLE Travel) Position. Knowing this can help when trying to determine if the breaker
Tripped off due to an overcurrent condition or was remotely turned off.
Auxiliary-Remote Alarm Switch
OCCASIONALLY It is advantageous to have an indication that
a breaker is open at a remote local. To facilities remote indication, some manuoFactures
provide a built-in form c (SPDT) contact set. The contal set may receive power from the
Breaker source by Internet
That require a fireign power source. by Foreign Power Source, I Inted to
Communicate that the form Contact Set is Not Powered from the Same Source of Supply
Of course going to the breaker s line terminals.
Group fault sensor
Some manufactures offer an external group fault sensor accessory.
These Devices Open The Circuit within A Pre-Established Time Period where
to group exceeds a pre-determined value. This occurs by detecting a current difference
Between Two or More Load Leads that has routed through an Air Core Current Transformer.
The Trip Current Set Point Values Are Higher for the Types of Devices than is Foundd
On COMMON MCCB TYPE GFCI (5 to 6 Ma Class a) Units. This is Becaude the Types of Sensorsors
Are Primarily Intented to Provement Protection for Equipment and not for people.
That some circuit breakers are provided with a group fault trip unit, when other are are,
Provided with an Alarm-only function for use with emergecy systems as required by the
NEC in Section 700-7 (d) and 700-26.
Under Voltage Trip
The UnderVoltage Trip Feature Will Operate The Circuit Breaker
When the support, Voltage Drops Below A Preset Value. Typically the Adjustable Range PROVIDED
is from 35 to 70% of nominal line voltage. This device incorporates a feature that prevents
The Breaker from Being Re-SETIL The Supply Voltage Returns to a Minimum of 85% of
Its normal level.
Lock-OUT/TAG-OET PROVISIONS
With this factory-installed accessory the task of performing
OSHA Required Lock-OUT/TAG-OF The Breaker is Made Easier and SAFER. With the device
Properly Installed and Locked, The Breaker Handle Cannit Be Moved to the Closed Position
From the Open Position.
Remote Operator Handle
OCCASIONALLY A BRL Will Be Installed in a Type of Enclosure
That DOES Not Allow Ready Access to the Breaker S Operator with the Door Closed.
MANY Manufactures Offer a Flexible Cable (or Rod) that is connected directly to the breaker s
Operator Handle At End and An External Mount Manual Switch at the Other End. The
Remote Operator Handle Is Typically Installed on A Flange Type Section of the Enclosure
And Performs The Opening and CLOSING of The Breaker Without the Need to Open the Enclosure S
door. The handle is pre-Drilled to Allow it to be locked in the open-off posity for
Safety. This feature Helps to Reduce the Risk Association with Arc Related Flash Burns.
The risk of flash buns have increased as our national genderlying, transmission, transmission, transmission, transmission, transmission,
And distributing capacity has increased over the year. The 2002 Edition of the NEC HAS
INTRODUCED SPECIFIC Requirements Intended to Reduce the Risk of Injury to Personnel from
Electrical Arc Flash Burns. These handles are sometimes drilled in the fire so that they they
May Also Be Locked in the On Position where it is determined by the ahj that safety is
enhanced to do so.
Stored Energy Breaker Operator
The two -tep Stored Energy Mechanism is using where a lot of of
Energy is required to operate the circuit breaker and when it needs to be closed or Opened
Rapidly to Minimize Arcing Related Damage. The two-only Energy Process is to charge
(Compress) The Closing Spring and THEN Release the Energy to Close the Breaker. This Method
UseS SEPARATE Opening and CLOSING Springs. This design permits the closing spring to be be
Charged Independedly of the Opening Process. Allowing for an open-close-popen duty cycle.
The Closing Spring Can Be Charged Manually Via A Charging handle or an internally moved
DC Electric Motor About the size of a 3/8 INCH DRILL MOTOR.
Remotly, Allowing for increased operator salty.
Once the Closing Spring is Charged, It Sits Compressed Ready
To rapidly re-close the breaker. Safety is enhanced with this type of operating mechanismmm
By Providing Remote (Motor Operating) Charging of the Spring and then Alowing the Breaker
To be remotely clooded. Should It Become Next, Provisions Have Been Provided by the
ManuFacture for Charging the Closing Spring Manually.
In the next part of this article the following topics will
be covered:
Molded Ciz Circuit Breakers
Molded CIRCUIT BREAKER Maintenance
If you have any questions or comments, please send me an e-mail.
Remember Work Smarter, Not Harder
L. W. Brittian
Mechanical-Electrical
Instructor
lwbrittian@hot1.net
Electrical Circuit Breakers
Part 6
In this the size part of the article covering circuit breakers,
The following topics are cover:
Molded Ciz Circuit Breakers
Molded CIRCUIT BREAKER Maintenance
MOLDED CASE CIRCUIT BREAKER (MCCB)
The Most Common Type of Re-Settable Overcurrent Protective
Device is the molded cases circuit breaker.
and to return in proper position the breaker s internahes. These cases are
MADE from various types of electrical insulting and file retardant plastic. Cases are are
Typically not hermetically sealed; this all to be subject to corrosion from environmental
Factors. They are limited to 600 VOLTS and Less. They are typically available in Either
Single, Two, or Three Pole Models. This type of circuit breaker is now available as afci,,,,,
GFCI, and Magnetic, Hydraulic-Magnetic, and THERMAL-MAGNETIC TYPES.
The book titled overcurrents and undercurrents
by Mr. E.W. Roberts, P.E. (ISBN: 0967432316) COVERS GFCI Type Devices.
Written, and is the only text that I am aware of that tovers afci s as if.
MOLDED CASE CIRCUIT BREAKER Maintenance (MCCB)
MCCB S HAVE MANY Years of Life Built Into them, Requiring
Little Maintenance. This Should Not Be Understood to Mean That Periodic Maintenance Is
Not required. NETA (International Electrical Testing Association Inc.) Has Developed and and
published a Book Titled Maintenance Testing Specifications (Neta-MTS-01) that
PROVIDES SOME Guidance as to How Various Types of Electrical Equipment Including McCB S,
And ICCB SHOULD Be Tested. Again you may have anticipated my next statement. i
Recomge that you obtain a Copy for your reference (303.697.8441).
Cost Money, But Not Knowing How Or what to do can count a lot more than just money, so
Try to talk the boss into purchasing it for you. In the interim, the followIn is a short
overview of some McCB Maintenance Tasks.
It is recoming that atreting once a Year a Properly Traine
and equiped qualified electrician perform the follow maintenance task:
Visually inspect the case to determine if any public
Indicates overheating; replace the breaker if overheating of indications are found.
Check connections for indications of overheating.
Cycle the breaker fire times manually.
Check and Record The Voltage Drop Across the Breaker USING
a Calibrald Digital Voltmeter
DECIMAL POINT).
The load shopping be operated at full load for the problem
Or unable the breaker reaches normal load testure; scan the breaker with an IR
Type Non-Contract Thermometer and Record the Readings.
Record Voltages and Note Any Voltage Imbalance from Phase
To Phase.
Current Readings Should Be Taken with A True RMS Type
Meter Due to the Increasing Harmonic Content in Many Electrical Systems in Commercial/Industrial
Facilities TODAY.
Current Readings on Equipment GROUNDING CONDUCTORS (where
Required) for Specific Machines Should Be Noted. Clamp on Type Group-Rod Circuit
Resistance Reading Meters Should be used for this task as they can detect both the
Impedance and the level ofurrent on the conductor if any is present, as Other Clamp
On type amp-meters will not indicate ma levels.
Breaker Test Sets Are Commercially Available From Several Sources
(Avo Multi Amp is One Source 800.723.2861). Testing of Circuit Breakers is a Vry Specialized
Area Requiring Special Training and Test Equipment and Should Be Conducted only by Competent
Personnel. NEMA HAS PUBLISHED A VALUABLE Guideline (AB-4-1991) that Should Be Consulted
when testing mccb s.
In the Seventh and Final PART of This Article The Following
Topics Will Be Covered:
MicroComPuter Circuit Breakers
Field Selectable Rating Circuit Breakers
Operation overView
Current Sensing
Continuous Amps
Long time delay
Short time pick-up-up
Short time delay
Instantaneous Current Pick-up Trip
Group fault current
Group fault pick-up
Group fault delay
Visual Annunciation-IDICATION LAMPS
Power consumption monitoring
Internet test
If you have any questions or comments, please send me an e-mail.
Remember Work Smarter, Not Harder
L. W. Brittian
Mechanical-Electrical
Instructor
lwbrittian@hot1.net
Electrical Circuit Breakers
Part 7
In this the final of the article counole
Follow Topics Are Covered:
MicroComPuter Circuit Breakers
Field Selectable Rating Circuit Breakers
Operation overView
Current Sensing
Continuous Amps
Long time delay
Short time pick-up-up
Short time delay
Instantaneous Current Pick-up Trip
Group fault current
Group fault pick-up
Group fault delay
Visual Annunciation-IDICATION LAMPS
Power consumption monitoring
Internet test
MicroComPuter Circuit Breakers
For Breakers in Size
the breaker s Response increases to the point that a microComputer-based circuit
Breaker Becomes Economical. Load Profiles in Many Commercial/Industrial Facilities Tend
to change over time and the ability to tailor a breaker specific performance aids
IN IMPROVING The Level and Types of Protection Provided for Both people and Electrical
Equipment. The Following OverView will present a Briefing to some of the more
Common Features Avaiilable in MicroComputer-Based Breakers that are available today.
The Adjustment of Any Circuit Breaker Should Not To Be Undertake
too lightly. Almost Anyone can turn a setting dial or enable
Program. It takes a fair amount of trade to be able to commission one of the computerized
Circuit Breakers Properly. Unless you have received the specification tocified needed to correctly
Adjust one of the units, I suggest that you do not attempt to do so so.
Task Ends and Electrical Engineering Begins Should Be Determined Before Any Adjustments
Are Undertaken. RECALL That Circuit Breakers Provide Not only Protection for Equipment,
But people as well.
Field Selectable Rating Circuit Breakers
SOME Manufactures Offer a Line of Breakers in the 500 to 5,000
amp range that have a replaceable rating plug. These rating plugs allow, for exmple,
a 400 AMP Frame Size Breaker to Be SELECTD from 200, 225, 250, 300, 350 or 400 AMPS BY
The Insertion of Matching Rating Plugs.
that was anticipating a major increase in load in a fears to initially select a 400
amp frame size breaker with a 225 amp rate plug to be installed. When the load increased
In the Future, The Breaker Could ITS AMPERAGE RATING Increased by the Quick Replacement
of the rating plug. Various Selectable Values for the Types of Breakers Are Based Upon
Either Percentages or Multiples of the Basic Continuous Current Rating of the Installed
rating plug.
Operation overView
Current data is Obtained for Each Phase from Current Transformers
(CT) MOUNTED Within The Breaker. The CT Output Signals are converted to digital values
And SENT to a MicroComputer. The microprocessor monitors each phase indicty at a
very high sampling rate. This is a key Improvement in Identifying Current and Voltage
WaveForms. The microComputer the Determines when the circuit breaker should try
To An Overcurrent Conition. An Electro-Magnetic Latch Unit in the Breaker Caut
Breaker to Trip Upon Receipt of A Trip Signal from the MicroComputer.
Shape of the Breaker S Time Current Curve to be manipurative electronically and to
be tailored to fore the desired performance propile in major every demy.
The Abilital to Field Program The Microprocessor To AccomPlish
The Desired Respourous Values of Time and Current Offers A Level of Circuit Protection
NEVER BeFore Possible. With the Addition of An External Communications Link (LAN or Ethernet
Type Gateway) Individual Breakers can be committed with, monitored, re-programmed,
Controlled, and Coordinated from Any Composition Connect Location, be it locally or from from
a distant center control room.
MANY of the Breakers have the ability to record pass events
Such as the cause of the indicting events, date and time of passt trips, voltage
And Current Values, or WaveForems on All Three PhaseS and the Neutral.
Current Sensing
The user of microComputers’ Allowed for Many Improvements
to be made in circuit propive devices. One area is in the sensing ofurrent. SOME
Breakers sense an average of the current, while Others sense only the peakurrents generated
in a sine wave. This is fine if the city s Current waveform is that of a true
sine wave, white few are.
The increase of ultra fast power switching devices has
Result in Harmonic Distortions Becoming Increasingly More Common. With MicroComputer-Equipped
Breakers, The True RMS Value Can Be Determined with Harmonic Distortions.
Is "
THEN USES the SAMPLES to Calculating The True RMS Value of the Load Current. This Allows
The breaker to perform faster, and with greater accuracy than ever beface.
The Afci Feature of Molded Case Low Voltage Circuit Breakers
Has Been Made Posses by Advances in Current Transformers Capable of Responding to Very
High Frequency CurrenTs; in Turn the MicroComPute Has Allowed the Data to Be Analyzed,
Classify, Plotted, Stored and When So Required to Be Displayed for Visual Review and
Analysis.
Continuous Amps
Continuous ampere is a percentage of the city breaker s
Normal Current Rating. Continuous amps can be adjusted typically from 20 to 100 % of the
Breaker S Nominal Rating (for Example, if the plug unit selected is 1,000 amps, 100
% WOULD BE 1,000 Amps. A Setting of 50% Would Result in Decreasing the Continuous Load
amps to 500 amps.
Long time delay
The long time delay causes the breaker to wait a certain amount
Of time to allow for tempory inrush, the such as aS those caused from motor
Starting Locked Rotor CurrenTs, Without The Breaker Tripping. The Long Time Delay Function
Setting is the length of time the breaker will hold an overload (running overcurrent)
BeFore Causing the breaker to open.
Short time pick-up-up
This function s setting will determine the amount ofurrent
The breaker will carry for a short time period, allowing down stream city
Devices to open the circuit and clear the fault withthout tripping the up stream breaker.
This allows for fine-tring of the selection clean function of the breaker.
This function is typically adjustedable from one and one half
To ten times the trip unit ampere setting. For exmple, a 1,000 ampere frame can be adjusted
To try anywhere from 1,500 to 10,000 amps. This is the amount ofurrent the breaker
Must see in order for it to respond.
Short time delay
The Short Time Delay is using in Conjunction with the Short
Time Pickup and Controls The Amount of Time Involved in Postponing A Short Time Pickup
Operation. This is the amount of time that mustbese beface causion
The circuit. This feature allows better coordination with downloading s.
Instantaneous Current Pickup
This feature s setting is used to try the circuit breaker
With No Intentional Delay at Any Current Typically Between Two and Forty Times The Breaker S
Continuous ampere setting. For exmple assume the instances pickup has set to ten
Times The Continuous Amp Setting or 10,000 AMPS (10 x 1,000) with a Continuous Amp Setting
of 1,000 AMPS. In this case a higher setting would trip at 10,000 AMPS DUE to a Fixed
Instantaneous override of 10,000 amps, white automatical trips the circuit breaker regardless
Of the Instantaneous Pickup Setting. If the Continuous Amp Setting Had Been 300 AMPS,
The Instaneous Pickup Setting at Ten Would Make The Instantaneous Setting Equal to 3,000
Amps, Well Below the Fixed Instantaneous Override. This function is Much the say as the
Magnetic Trip Unit S Instantaneous Pick-Up only ProgramMable for the Specific Needs
of the unique installation.
Group fault current
Typically An Led Type of Display Provides a Reading of the
Number of Amps Flowing Across the Equipment Group Conductor.
Can be utilized with a display module or a relay that has a set of contacts for a group
fault Alarm. When used with a shunt trip equipped breaker, a ground fault monitor can
Be used for group fault tripping of a breaker equipped with a shunt trip feature.
Group fault pickup
This adjustment controls the amount of group fault can
That Will Cause the Breaker to open. These Adjustments Typically Range from 20 to 70%
of the maximum breaker rating in compliance with article 230.95 (a) of the nec that no
Pickup setting exceeds 1200 amps. GROUND FAULT PICKUP is sometimes divided into sections
that allow various time delay value
a ground fault occurs. This feature is useful for improving circuit breaker coordination
With both up and down stream propective devices.
Group fault delay
This is the time period that must pass before the breaker trips.
This feature s setting is typically one of two types, an inferse time or a constant
Amount of time delay.
of group fault Current Increases. Please recall that the longer a fault exist and the
Higher The Current Flowing in the Faulted Circuit, The more portal danger and damage
There will be. The constant amount of time methodiains the time delay per later
The say no music what the amplitude of the fault can may be.
Visual Annunciation-IDICATION LAMPS
Depending upon the brand and model, various lights give the
User a Means for Visually Determing what kind of fault caused the breaker to open. Typically
Indicator Lamps are provided for indecent of long time fault, short time fault, instantaneousous
fault, and group fault events.
Power consumption monitoring
SOME MODELS Can Be Equipped with Features to Assist in Monitoring
Electrical Energy Consumption.
Alarm Set Points May Also Be PROVIDED on Some Models. Various Communication Protocols
Are used by Individual Manufactures. With increasing concess of power quality, this, this
Feature is Being Expanded to Include Factors Relacted to Power Quality and Not Just Power
Quantity.
Internet test
This feature enables the user to test the microComputer S
Trip Circuit S Electronics, The Electro-Magnetic Latch and Power Contory Set Opening
Mechanism. The Purpose of this test function is to provide the user with an easy means
To ConDuct A Quick Go-NO-GO TEST BeFore Bringing The Circuit Breaker on-Line to
Protect and pass power to the connected loads.
SOME Manufactures Povide for Some Degree of Automatic Testing
Each Time The System Frame Circuit Breaker Fixed Switch ODM ManuFactuer is PowerEd Up. With Yet Others Individual Test are manually
follow predetermined steps.
DONE Until all of the field selectionable and variable value, or default
VALUES (where provided) have ben selected.
COVERED Under the Label of a Watchdog Timer that Monitors the Processor S
Health for Indicatings of Non-Performance (Within Specified Times).
Electrical Devices has long ben out of the lab and has ben,
Plant Floor.
If we can give Mr. Edison One of the Modern Replacements
For his lead wire fuse, I wonder what he would do with it? My bet is just what manualsUfactures
Are doing today, try and make them ball.
Environmental Impact Statement
I do not intend what you likely anticipate that the about implies.
No man is an island. That is the reals that go on design each of us (our
Environment) have an impact upd each of us, and boy oh boy has been impacted. So much.
So that I do that there is a single Original IDEAINED in the Pages. From my
FIRST GRADE ABC S Teacher to More than One Professional Electrical Engineer, LOTS
Of good folks have directly and indirectly Helped me to write this article, so many so
That I cannot obcurately recall all of them. Intead I chose to list only one. Mr. Holt
From Center of my bebing thanank you! .. Sir. May God Bless and Keep You And YourS Safe!
This concludes this series of Articles Covering Circuit Breakers.
I hope that you will control your study of circuit and overcurrential devices.
If you have frame circuit breaker fixed switch odm manufacturer any questions or comments, please send me an e-mail.
Remember Work Smarter, Not Harder
L. W. Brittian
Mechanical-Electrical
Instructor
lwbrittian@hot1.net