Setting of overload, Short circuit & Ground Fault Protection of MCCB (PART-1)


Introduction:

  • There are various types of protections setting in MCCB, which define various protection of Electrical Network.
  • In MCCB we can set most of protection are adjustable according to Electrical Load profile.
  • The main adjustable Setting in MCCB are
  • Over current Setting
  • Short Circuit Setting
  • Ground Fault Setting

Meaning of each selector switches of MCCB

  • As Per Standard IEC 60947-2 defines the names of the selector switches.
Setting Adjustment Protection For
Ir Long time Pick up Current Setting (or thermal Setting). This is a multiplication coefficient of the rating of the device. (Ir=xIn) Protection against overloads
tr Long time delay Setting in seconds, enabling in particular the starting current of a motor to be tolerated. (tr=Sec) Protection against overloads
Im / Isd Short time (Magnetic Setting). This is a multiplier of the Ir setting, often 1.5 to 10 times the Ir current (im=xIr) Protection against short circuits.
tm / tsd Short time delay Setting, enabling in particular the discrimination (time) to be increased with downstream feeders and the magnetization peaks of a transformer or a motor to be tolerated. It is recommended that the I²t selector switch is set to the ON position.(tm=Sec) Protection against short circuits.
Ii Instantaneous current Setting. Protecting the installation against strong short circuits (dead short circuits) by instantaneous tripping without Time Delay and self-protection of the circuit breaker.

The Ii > Isd.

Protection against Dead Short circuits.
Ig for monitoring the earth fault current circulating in the Phase and Earth conductor in TNS systems Earth protection
tg Earth protection time delay Earth protection
I delta n Adjustment of the sensitivity of the earth leakage protection Earth leakage protection
delta t Earth leakage protection delay. Earth leakage protection

  Setting of each Protection switch of MCCB

 (1) For Low level Fault / Over Current Protection (Thermal Setting):

  (A) Long-Pickup Current Setting (Ir):

  • It is determines the continuous ampere rating of the breaker.
  • Long time protection is time-dependent.
  • Long Pickup (Ir) value (multiplied by the ampere rating (In) of MCCB) sets the maximum current level which the circuit breaker will carry continuously.
  • If MCB is 1000A Rating but Full Load current is 800A than MCCB Rating can be changed from 1000A to 800A by setting it 0.8, Now Ir=0.8XIn =0.8×1000=800Amp
  • If the current exceeds this value for longer than the circuit breaker will trip at the set delay time.
  • Long time protection is inverse time type (with I2t constant)
  • The long-time pickup (Ir) is adjustable from 4 to 1.0 times the sensor plug rating (In)
  • Standard Practice for Setting:
  • No trip for a current below 105% of Ir
  • Trip in less than two hours for a current equal to for
  • 120% of Ir for an electronic trip unit and for
  • 130% of Ir for a thermal-magnetic trip unit
  • For a higher fault current, the trip time is inversely proportional to the fault current value.

(B) Long-Time delay Setting (tr):

  • Long time delay (tr) sets length of time that the circuit breaker will carry a sustained overload before tripping.
  • The delay bands are labeled in seconds of over current at six times the ampere rating.
  • Long-time delay is an inverse time characteristic in that the tripping time decreases as the current increases.
  • The long-time delay (tr) sets the length of the time that the circuit breaker will carry an over current (below the short-time or instantaneous pickup current level) before tripping.
  • The Long time delay can be set to I2t On and I2t OFF settings.
  • (A) I2t Response:I2t Out ,For coordination with other circuit breakers with electronic trip devices and for coordination with thermal-magnetic circuit breakers.
  • (B) I2t Response: I2t In ,For coordination with fuses and upstream transformer

 

 

 

 

 

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Type of Tripping Mechanism of MCB / MCCB-(Part-2)


(3) Thermal-Magnetic Trip mechanism (inverse-time & instantaneous-trip)

  • Thermal-magnetic circuit breaker (TMD) is most common use for over current and short circuit protection.
  • It is a combination of Thermal Circuit breaker and Magnetic Circuit Breaker.
  • It contain two different switching mechanisms, a bimetal switch and an electromagnet
  • The thermal Property (Bimetal Strip gets elongated when heating) is used to sense the overload and Magnetic Property (Magnetic Flux / induction) is used to sense the short circuit.
  • Characteristic:
  • In Thermal-Magnetic Circuit Breaker both Thermal element (Bimetallic Strip) and Magnetic element (Electromagnet) are connected in series with load.
  • In normal Load a bimetallic element is heated by the normal load current, the bimetallic element does not bend, and the magnetic element does not attract the trip bar.
  • If the temperature or current increases over a sustained period of time, the bimetallic element will bend, push the trip bar and release the latch. The circuit breaker will trip.
  • If the current suddenly or rapidly increases enough, the magnetic element will attract the trip bar, release the latch, and the circuit breaker will trip.
  • Thermal Trip gives inverse time characteristic and Magnetic Circuit Breaker (instantaneous-trip circuit breakers) gives instantaneous-tripping.
  • MCCB Rating: 10 A to 1600A
  • Operating Time: 4mili sec.
  • Application:
  • For residential Load
  • For to heavy industrial loads.
  • For higher level (short circuit) over currents,
  • For motor-circuit protection.
  • AC/DC power distribution.
  • Electrical machines
  • Protection for transformers, motors, generators.
  • For Protection of capacitor.
  • Protection Range:
  • The adjustable overload protection is from 70% to 100% of the nominal current (0.7 to 1xIn)
  • Short circuit setting from 5 to 10 times of the rated current is possible.
  • For example: A 100 A thermal-magnetic circuit breaker will trip within a short time if it is subjected to a current of 400 A, but a 100 A instantaneous-trip circuit breaker will carry that overload indefinitely, if the adjustable trip is set above that level.
  • Instantaneous-trip circuit breakers are circuit breakers that have a magnetic trip function but not a thermal trip function. They are designed for one very specific purpose, that being to provide branch-circuit short-circuits protection for motor circuits.
  • Advantage:
  • economical, tried and tested technology
  • Disadvantage:
  • The operating characteristics of the breaker may vary depending on the ambient temperature.
  • It needs particular time to trip ( heat up the metallic strip > open circuit the holding coil > opens the contacts
  • Provide less flexibility of adjustment than electronic releases.

  (4) Electronic (Static) Trip Mechanism:

  • A coil, placed on each conductor, continuously measures the current in each of them.
  • This information is processed by an electronic module which controls the tripping of the circuit breaker when the values of the settings are exceeded.
  • Both the overload trip action and the short-circuit trip action of breakers with electronic trip units are achieved by the use of current transformers and solid-state circuitry that monitors the current and initiates tripping through a flux shunt trip when an overload or a short circuit is present.
  • MCCB Rating: 20 A to 2500A
  • Operating Time: 4mili sec.
  • Protection Range:
  • The adjustable overload protection is from 60% to 100% of the nominal current (0.6 to 1xIn)
  • Short circuit setting from 2 to 10 times of the rated current is possible.

 

  • Advantage:
  • The operating characteristic of the breaker is independent of the ambient temperature. 
  • More accurate and more flexible settings
  • Becoming standard for larger size breakers
  • Ground fault easy to provide
  • It has wide flexibility to takes care of future increases in load capacity of an installation and ensures better planning at an optimum cost
  • Disadvantage:
  • It is costly compare to TMD Type MCCB.
  • Application:
  • Electronic trip breakers are generally applied for applications where high levels of system coordination.
  • Electronic trip breakers can provide superior protection and coordination as well as system alarms and diagnostics, monitoring and communications.

(5)  Microprocessor Trip Mechanism:

  • In Microprocessor type tripping mechanism release, sensing and tripping executed by Microprocessor by use of CT or current sensing resistor
  • It gives the very faster response than TMD Release.
  • MCCB Rating: 20 A to 2500A
  • Operating Time: 4mili sec.
  • Protection Range:
  • The adjustable overload protection is from 60% to 100% of the nominal current (0.6 to 1xIn)
  • Short circuit setting from 2 to 10 times of the rated current is possible.
  • Advantage:
  • System Diagnosis is possible as it stores the Trip history within the internal memory.
  • Trip current indication is also available for understanding of type of fault and set-up programming at site. 
  • High repeat accuracy and High reliability.
  • Provide coordination, Interlocking to other MCCB.
  • High Flexibility
  • Disadvantage:
  • It is costly compare to TMD Type MCCB.

Type of Tripping Mechanism of MCB / MCCB-(Part-1)


Introduction:

  • Moulded Case Circuit Breakers are electromechanical devices which manually / automatically protect / Open a circuit from Over current and Short Circuit. There is various type of Tripping mechanism to trip MCB/MCCB.

MCCB Tripping Mechanism:

MCCBs have following various Operating Mechanisms.

  • Thermal Trip
  • Magnetic Trip
  • Thermal- Magnetic Trip 
  • Electronic Trip 
  • Microprocessor Trip

 (1) Thermal Trip Mechanism (Inverse-time)

  • The thermal trip mechanism of MCCB works as a delay fuse.
  • It will protect a circuit against a small overload that continues for a long time.
  • In Thermal trip MCCB a bimetal strip is connected in series with the circuit load.

1

  • When normal current pass through bimetallic strip and rise temperature of bimetallic strip and it increase length of bimetallic strip but this expansion rate is not enough for bending movement of strip and the contacts will remain closed.
  • As current of MCCB increase beyond over load current. It heats enough bimetal and thus bimetallic strip bend as per current level and Close contact will be open.
  • The amount of current needed to trip the MCCB depends on the size of bimetallic Strip.
  • The time the bi-metal needs to bend and trip the circuit varies inversely with the current.
  • It has Inverse time characteristics, they allow a long-time delay on light overloads and they have a fast response on heavier overloads.
  • The thermal element will also protect the circuit against temperature increases.
  • It is Sensitive to ambient temperature
  • MCCB must carry 100% of rated current continuously at 40 deg C.
  • At 200% rated current, maximum trip times are

                              Trip Time of Thermal Element @200% current

Amp Rating Max Time @ 200%

0-30

2 min
31-50 4 min
51-100 6 min
101-150 8 min
151-225 10 min
1601-2000 28 min
  • Tripping Action: Tripping Time will depend upon Current. The larger the overload, the faster the circuit breaker will trip
  • Used For: Over Load Protection

 (2) Magnetic Trip Mechanism (Instantaneous-trip)

  • In magnetic trip MCCB an electromagnet (an iron core with a wire coil around it, forming an electromagnet) is in series with the circuit load.

2

  • With normal current, the electromagnet will not have enough electromagnetic field to attraction the trip bar for movement and the contacts will remain closed.
  • As High current (Short Circuit) current through the coil increases the strength of the magnetic field of the electromagnet. As soon as the current in the circuit becomes large enough, the trip bar is pulled toward the magnetic element (electromagnet), the contacts are opened and the current stops.
  • The amount of current needed to trip the MCCB depends on the size of the gap between the trip bar and the magnetic element.
  • On some MCCB this gap (trip current) are fixed and some MCCB are adjustable.
  • Tripping Action: A magnetic circuit breaker will trip instantly when the preset current is present.
  • Used For: Short Circuit Protection

Type of Light Bulb base & Socket:Part-2


(4) Single Pin Type Base (F):

1

  • The “F” type of lamp base is used to as a “pinned” base.
  • This Type of socket have Single Pin.
  • Type of Connection: “Pin” Type
  • Pin Configuration: (Fx):

(5) Cable connected Socket (K):

  • 2.jpgAction: “Cable” Type
  • Pin Configuration: K
  • K indicates that a cable is the power connection for a lamp.
  • The product is a wired connection to power.
  • Example: K4 , K6
  • Application:
  • with standardized connecting cable for electrically operated valves, mechanical position switches and valves with central connection

(6) Pr-focused Sockets (P):

3

  • Action: “Push” Type
  • Pin Configuration: P
  • Types:
  • LED light bulb pre-focus base types: S.C. Prefocus and D.C. Prefocus 
  • Application: Automobile

(7) Recessed Contact Base (R)

4.jpg

  • Action: “Spring Loaded”
  • Pin Configuration: (Rx):
  • Here “R” indicate recessed Type Socket.
  • Recessed Double Contact Base used for Fluorescent type lighting bulbs having high output.
  • Applications
  • For Fluorescent type lighting bulbs

(8) Flange base Sockets (F or T):

  • Action: “Push” Type
  • Pin Configuration: F or T5
  • Type of Flange Base Socket: Micro-midget flanged base, Midget flanged, Miniature midget flanged, Sub-midget flanged, and Special-midget flanged base types.
  • Application: LED light bulb, Electrical Panel, Indication Lamp, Automotive, Electronic device lighting applications. 

(9) Slide base Sockets (S):

6

  • Action: “Push” Type
  • Pin Configuration: S
  • Type:
  • There are various types like Slide#1 ,Slide#2
  • Slide base LED replacement bulb is perfect for industrial indicator lights.
  • It is also used as an LED pilot light bulb.
  • Applications
  • Indicator LED replacements
  • LED Pilot light bulb

(10) Wedge base Sockets (W):

7

  • Action: “Push” Type
  • Type: Double Side (D.F) Contactor and Single Side (SF) Contactor
  • Pin Configuration: (WX2.5x16q):
  • W =Wedge Type, Second Letter indicate the width in millimeters and third lowercase d to indicate a double-contact (single-filament) bulb or q for a quad-contact (dual-filament) one.
  • A wedge base is a type of connector used as a fitting for small light bulbs in Automobile. It is same as bi-pin connector, except that the two “pins” are the same wires that extend into the bulb (rather than being rigid), and the wires are bent up onto the sides of the base, where they make contact with the socket.
  • The wires are usually inserted into a plastic base that the bulb is mounted in, and which is often narrower at the tip than at the bulb, giving it a wedge shape and usually ensuring a tight connection.
  • The bulb is inserted and removed with straight in or out force, without turning as with a bayonet mount or Edison screw. compression is the force that holds the bulb in
  • Application: In Automobile and in low-voltage lighting used in landscape lighting.

Type of Light Bulb base & Socket:Part-1


Introduction:

  • A lamp holder is the device which holds a light bulb or lamp. It’s important that the lamp holder is compatible with the type of bulb we want to use, with the wrong base selection will not fit in the lamp or fixture.
  • Light bulb sockets are normally defined by a letter-number-letter (Third Letter is optional).
  • The first letter indicates the shape of the base.
  • The Second numbers indicates either the width of the base or the distance between the pins.
  • The Third Letter indicates the number of pins or contacts on the lamp. The numbers are normally in millimeters.

Type of Sockets:

There are different types of Socket available in market

  1. Bayonet Cap Base (B)
  2. Edison Screw Cap Base (E)
  3. Single Pin Type Base (F)
  4. Bi Pin or Multi Pin Type (G)
  5. Cable Connections (K)
  6. Pre- focused Light Base (P)
  7. Recessed Contact Base (R)
  8. Flange Base Light Bulb Base (F or T)
  9. Slide Base (S)
  10. Wedge Base (W)
  11. Special Type Light bulb Base (X)

(1)  Bayonet Cap (B / BC / SBC):

1

  • Type of Connection: “push and twist” action
  • Pin Configuration: (Bxx or BCxx):
  • The First letter indicates the shape or Style of the base.
  • The Second number indicates the width of the base (normally in millimeters).
  • Example:
  • The “B” refers to the style of Base which is a Bayonet, and the 22 means it has a 22 mm base width.
  • Application: All Regular type of Bulbs including specialist low voltage halogen lamps

(2) Edison Screw Cap (E / ES):

  • Named as inventor Thomas Edison, the Edison Screw or “ES” lamp fitting is used in a vast range of applications.

2

  • Type of Connection: “Screw” Action
  • Pin Configuration: (Exx or ESxx):
  • The First letter indicates the shape or Style of the base.
  • The Second number indicates the width of the base (normally in millimeters).
  • Example: E26 base.
  • The “E” refers to the style which is an Edison screw-in, and the 26 means it has a 26 mm base width.
  • Application: Large chandeliers Some Decorative Lamps.
  • The most commonly used screw fittings are shown in the table below. Other, less frequently used, sizes include E11, E17 and E26.
Designation Diameter Name Abbreviation
E5 5mm Lilliput Edison Screw LES
E10 10mm Miniature Edison Screw MES
E12 12mm Candelabra Edison Screw CES
E14 14mm Small Edison Screw SES
E17 17mm Intermediate Edison Screw Base IES
E27 27mm Medium Edison Screw ES
E39 39mm Mogul or Giant Edison Screw Base GES
E40 40mm Giant Edison Screw GES

(3) Bi Pin or Multiple Pin Type Base (G)

3

  • The “G” type of lamp base is used to as a “pinned” base. This may be several Numbers of different Types of pins.
  • Type of Connection: “Pin” Type
  • Pin Configuration: (G(U,X,Y,Z) -xx-x-x):
  • It is indicate by Letter (or Letters)-Numbers-Optional letter- Letter:
  • The first letters includes “G” which is followed by a Second (optional Letter) Letter U, X, Y or Z.
  • The second letter (U, X, Y,Z) represents the configuration of the base, which determines the diameter and shape of the pins. For example, pins may be rounded, square, grooved, fat or slender.
  • Without any Optional Letter = Base length is 8.25mm and Pin Diameter is 0.7mm
  • For Y=Base length is >6mm and Pin Diameter is 0.7mm
  • For X= Base length is <7.5mm and Pin Diameter is 1mm
  • For U= Base length is >6mm and Pin Diameter is 1mm With One or Two Grip channel.
  • For Z=P Base length is >6mm and Pin Diameter is 1mm without Grip Channel.
  • The Third number indicates the Distance in millimeters between the centers of each pin.
  • The Forth (optional Letter) Letter indicate the number of pins, no letter means 2 pins. d for double Pin ,s for Single pin, t for Triple pin or 3 pins and q for Quadruple pin or 4 pins.
  • The Fifth Letter indicates position of Dowel (Slot) in Socket
  • Examples: GU10 base type, GU24q 2Pin base type, G13d 3pin.
  • For GU24q 2 Socket, U=Pin length is>6mm with diameter 1mm with Grip channel, No of Pin is 4 no’s and Dowel is on Left Side
  • Application: Halogen, Compact Fluorescent ,LED Types Bulbs

 4

Difference between G24q-1, G24q-2, G24q-3 Type Socket

  • Here G=Type/ Shape of Socket
  • 24=Distance between each Pin
  • q= Quadruple (Four) Pin.
  • 1=Indicate Dowel (Slot) Position ,1=Middle, 2=Left, 3=Right Position

5
Difference between Gx24, G24 Type Socket

  • In Gx24 The Base is smaller while in G24 Base is larger.

6

Type Pin to pin distance Pin Diameter Typical Bulbs that use this base
G4 4mm 0.65-0.75mm MR11 and other small halogens of 5/10/20 watt and 6/12 volt
GU4 4mm 0.95-1.05mm
GY4 4mm 0.65-0.75mm
GZ4 4mm 0.95-1.05mm
G5 5mm T4 and T5 fluorescent tubes
G5.3 GU5.3 GX5.3 GY5.3 5.33 mm 1.47-1.65mm MR16 and other small bulbs typically using 12/24 volts
G6.35 GX6.35 GY6.35 6.35 mm 0.95-1.3mm
G8 8mm
G9 9mm
GU10 10mm bulbs using twist-lock bi-pin base
G13 12.7mm T8,T10 & T12 fluorescent tubes
G23 23mm 2mm
GU24 24mm 2 and 4 pin bases with center key
GX53 53mm used with puck shaped lamps typically twist-lock

How to select MCB / MCCB (Part:3)


(E) Others:

 (1) Frequency:

  • MCB is designed and used in AC power system of 50 to 60Hz.
  • Electromagnetic force of magnetic release is related with power supply frequency so If Frequency is changed than electromagnetic fore of Magnetic element is changed hence MCCB tripping current will be different.
  • If we used MCCB for protection in DC circuits than specially design DC circuit MCCB should be used rather than normal type of MCCB.

(2) Isolation:

  • MCCB is suitability for visible isolation. It is particularly important.
  • If a circuit breaker is turned off, it should indicate so visibly.
  • It should not be able to indicate otherwise if the contacts are not open. In other words, it offers proof of isolation.

(3) Type of Mounting Arrangement:

  • According to mounting arrangement, MCBs can be divided into two categories.
  • DIN rail mount MCCB
  • Plug-in MCCB
  • DIN Rail Mount MCB
  • The main advantage of this type of MCB is versatility
  • DIN rails are used by many different types of electrical and communications equipment, and they are mainstream in industrial settings.
  • They can be easily integrated into nearly any control or protection system.
  • A disadvantage of this type of MCB is that more work is required for installation, and plug-in MCBs may be a better choice for simple installations.
  • Plug-In MCB
  • These MCBs are easy for installation. As name indicates, they just have to be plugged into a compatible electric panel.
  • Plug-in MCBs are suitable for applications that use circuit breakers exclusively- typically residential and commercial electrical distribution systems.
  • When using plug-in MCBs it is important that the breakers and the panel must match. It is not an issue when both are of the same brand

(4) Pollution degrees:

  • It determines in what kind of environment circuit breakers can be installed.
  • In a Domestic purpose where there is no dust no humidity, the circuit breaker is comfortable.
  • For Domestic purpose pollution degree 2 is suitable.
  • But in an outdoor public installation where there may be dust which cause leakage currents and lead to dangerous arcs.
  • For dusty pollution, humidity environment or outdoor type heavy-duty applications (incoming switchboards) pollution degree 3 is suitable.

(5) Energy Class:

  • MCB need some time for tripping, In this time, fault current will create some energy which will exist in system.
  • This energy is termed as release energy. For efficient MCB operation it should be in within limited. On basis of amount of release energy it is classified in class 1, class 2 and class 3.
  • Class 3 is best which allows maximum 1.5L joule/second.

 Example of MCB / MCCB specification / Name Plate:

Frame: F750
Rated Operational Voltage (Ue):        415V
Rated Insulation Voltage (Ui) : 690V
Rated Impulse withstand Voltage (Uimp): 6KV
Rated Current (Ie) : 80A
Ultimate Breaking Capacity (Icu): 10KA
Service Breaking Capacity (Ics) : 75 % of Icu
Utilization Category : A Type
No. of Poles:   3
Suitability for Isolation: Yes
Electrical Life Cycles : 5000
Mechanical Life Cycles:         25000
Release Type : Thermal – Magnetic
Thermal:          Fixed
Magnetic: Fixed
Terminal Capacity Cable: 50 mm2
Dimensions (mm) WXHXD : 75X130X60
Weight:            0.84Kg
Operating Temp Range:  -5 to +50°C
Reference Temperature: 50°C

 Main factors affected on cost of MCCB for same rating

  • Short circuit Capacity
  • No of Poles
  • Type of Application (Characteristic Type)
  • Type of Trip Mechanism (Thermal-Thermal-Magnetic, Solid, Microprocessor)
  • Accessories

 What should we select MCB or MCCB

The selection of MCB or MCCB depends upon your application. Main difference between MCB and MCCB is

Characteristics MCB MCCB
Standard IEC60898-1 IEC60947-2
Rated current 6A to 100A 10A to 2500A.
Interrupting rating Up to 18KA 10KA to 200KA
Trip Mechanism Thermal / Magnetic Thermal / Magnetic / Static
Trip characteristics Settings Not  adjusted Fixed /Adjustable

Thermal operated for overload and Magnetic operation for instant trip in Short circuit conditions

Application Indoor Type Indoor / Outdoor Type
Pollution Degree 0 to 2 3
Suitable for Low current circuits (homes, shops, school and offices). High power rating i.e. commercial and industrial use
User This is designed for unskilled user / uninstructed user and not being maintained consequently This is designed for skilled user and supposed to be maintained properly
Type of Protection over current protection over current / Short Circuit / Earth Fault  protection
Mounting Rail Mounted Rail / Fixed / Draw out Mounted
Operating Mechanism Electrical /Mechanical Operating Electrical /Mechanical / Motorized Operating
   untitled  22

 Example: what should we select MCB or MCCB for current carrying capacity 100A and breaking capacity 15KA and cost is a not main criteria.

  • For this rating both MCB and MCCB are available so we should consider application and other facilities to choose MCB or MCCB.
  • If we want to use it at indoor purpose, having less Space and if we do not need tripping adjustment  and other function or accessories than MCB is best option.
  • If we want to use it at indoor / Outdoor purpose, having Space and need tripping adjustment for coordination with other MCCB, We need Interlocking for safety and other function or accessories than MCCB is best option.
Characteristics IEC 60898-1 (MCB) IEC 60947-2 (MCCB)
Rated Current: In 6 – 125A 0.5 – 160A
SC Breaking Capacity <25kA <50kA
Rated Voltage: Ue 400V 440V, 500V, 690V
Impulse Voltage: Uimp 4kV 6kV – 8kV
Pollution Degree 2 3
Curves B,C,D B,C,D,K,Z,MA
Application Current AC AC or DC
Application Residential Residential / Commercial / Industrial

How to select MCB / MCCB (Part:2)


(C) Application Type:

(9) Utilization category / Characteristic (B, C, D, K, Z curve):

  • Characteristic of Trip curves of MCCB tell about the trip current rating of MCCB.
  • MCB will trip instantaneously according to their Tripping Characteristic at 0.1 sec.
  • There are various type of MCCB
  • Type B MCCB
  • Type C MCCB
  • Type D MCCB
  • Type K MCCB
  • Type Z MCCB

 11

 Type B MCCB:

  •  Operating Current: This type of MCB trips between 3 and 5 times rated current (In).
  • Operating Time:04 To 13 Sec
  • For example a 10A device will trip at 30-50A. 
  • Application: Domestic applications or light commercial applications where connected loads are primarily lighting fixtures, domestic appliances with mainly restive elements.
  • Suitable for: Restive Load application (Lighting , Small Motor)
  • Surge Current: The surge current level is relatively low.
  • Installation at: At Sub feeder of Distribution Board.

   Type C MCCB:

  •  Operating Current: This type of MCB trips between 5 and 10 times full load current.
  • Operating Time:04 To 5 Sec
  • Application: commercial or industrial type of applications, fluorescent lighting, motors etc where there could be chances of higher values of short circuit currents in the circuit.
  • Suitable for: Inductive Load application (Pumps, Motor, fluorescent lighting.)
  • Surge Current: The surge current level is relatively moderate level.
  • Installation at: At incoming / Outgoing of Distribution Board.

Type D MCCB:

  • Operating Current: This type of MCB trips between 10 and 20 times full load current.
  • Operating Time:04 To 3 Sec
  • Application: specialty industrial / commercial uses (Transformers or X-ray machines, large winding motors, discharge lighting, large battery charging). Where current inrush can be very high.
  • Suitable for: Inductive- Capacitive Load  application (Pumps, Motor)
  • Surge Current: The surge current level is relatively High
  • Installation at: At incoming of Distribution Board / Panels.

Type K MCCB:

  • Operating Current: This type of MCB trips between 8 and 12 times full load current.
  • Operating Time:04 To 5 Sec
  • Application: Suitable for inductive and motor loads with high inrush currents.
  • Surge Current: The surge current level is relatively High
  • Installation at: At incoming of Distribution Board / Panels.

Type Z MCCB:

  • Operating Current: This type of MCB trips between 2 and 3 times full load current.
  • Operating Time:04 To 5 Sec
  • Application: These types of MCBs are highly sensitive to short circuit and are used for protection of highly sensitive devices such as semiconductor devices.
  • Surge Current: The surge current level is relatively too low
  • Installation at: At Sub feeder of Distribution Board for IT equipment.

(D) Accessories:

(1) Rotary Handle:

11

  • It is used to extend ON/OFF handle of MCCB when Panel Door is closed.
  • It is also used to indicate ON/OFF or Trip Position

(2) Shunt Trip:

33

  • Used for Remote Tripping

(3) Alarm contact:

22

  • It gives Tripping Indication when MCCB Trip.
  • It does not give when MCCB is in normal condition (either ON or OFF)

(4) Auxiliary contact:

33

  • It used for remote signaling and control purpose.
  • It is also give ON/OFF indication of MCCB at remote location.

(5) Under Voltage Tripping:

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  • It used to trip MCCB in under voltage condition (70 to 35% of rated Voltage).

(6) Mechanical Interlocking:

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  • It used to mechanical interlock of two MCCB on the same Panel.

(7) Manual / Auto:

  • MCCB may have provision for Auto /Manual operation.
  • An “auto/manual” switch in front of Panel.
  • When set to the “Manual” position, lock out electrical control and when set to “auto”, lock out the manual control; remote indication

(8) Motorized operation:

  • MCCB may have option for manual operation or with a motor mechanism for electrically controlled
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