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


  • 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.


  • 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%


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.


  • 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):


  • 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):


  • 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)


  • 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):


  • 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):


  • 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


  • 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):


  • 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.


  • 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)


  • 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


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

Difference between Gx24, G24 Type Socket

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


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


 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:


  • 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:


  • Used for Remote Tripping

(3) Alarm contact:


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

(4) Auxiliary contact:


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

(5) Under Voltage Tripping:


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

(6) Mechanical Interlocking:


  • 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

How to select MCB / MCCB (Part:1)


MCB or MCCB are widely used in electrical distribution system for ON/OFF Electrical supply and it also gives over current and short circuit protection. Selection of MCB or MCCB involved technical, Mechanical parameters. Some parameters are important but some parameters are confusing and mislead to wrong selection of MCCB. Some parameters are directly affected on cost of MCCB.  

Specification / Name Plate Details of MCB/MCCB:

 Following specifications are required to select appropriate MCB or MCCB.

(A) Current Related:

  • Frame Size (Inm): Amp
  • Rated current (In/ Ie): Amp
  • Ultimate short circuit breaking capacity (Icu): KA
  • Rated short-circuit breaking capacity (Ics): % of Icu

(B) Voltage Related:

  • Rated voltage (Ue): Volt
  • Rated Insulation voltage (Ui): Volt
  • Rated impulse withstand voltage(Uimp): KV
  • No’s of Pole : SP,DP,TP,TPN,FP

(C) Application Type:

  • Utilization Category/ Characteristic : B,C or D curve

(D) Accessories:

  • Rotary Handle: Extended/ Direct
  • Alarm Contact:
  • Shunt Trip:
  • Under voltage Trip:
  • Mechanical interlocking:
  • Manual /Auto operation
  • Motorized Operation:

(E) Protection Type:

  • Protection : Over current / Short circuit
  • Trip Mechanism: Thermal / Magnetic / Solid / Microprocessor
  • Trip Mechanism adjustment : Fixed / Adjustable

(F) Others:

  • Frequency;
  • Reference temperature: (if different from 30°C)
  • Pollution degree:
  • Suitability for isolation:
  • Type of Mounting arrangement
  • Electrical Life Cycles:
  • Mechanical Life Cycles:
  • Dimension: mm
  • Weight: Kg
  • Reference Standard: IEC: 60947-1/2, IS: 13947-1/2

 (A) Current Related:

  (1) Frame Size (Inm): 

  • Breaker Frame Size indicates the basic framework of the Plastic shell of MCCB that can hold the biggest rated current.
  • It is the maximum current value for which the MCCB is designed (upper limit of the adjustable trip current range) and it also determines the physical dimensions of the device.
  • There are varieties current ratings MCCB for the same series frame Size.
  • For example, DX100 Frame Size MCCB for rated current of 16A, 20A, 25A, 32A, 40A, 50A, 63A, 80A, 100A.
  • Same DX225 Frame Size MCCB for rated current of 100A, 125A, 160A, 180A, 200A, 225A.
  • In above DX100 and DX225 has two Type of frame Size for rated current of 100A, but the shape and size of breaking capacity of circuit breakers is not the same.

 (2) Rated Current (In /Ie):

  • It is the current value above which overload protection is tripped.
  • For MCB it is fixed while in MCCB the rated current is an adjustable range instead of a fixed value.
  • Standard rating of MCB is 1A, 2A, 3A, 4A, 6A, 10A, 13A, 16A, 20A, 25A, 32A, 40A, 50A, 63A, 100A for MCB.

(B) Voltage Related:

 (3) Ultimate short-circuit breaking capacity (Icu):

  • Breaking capacity can be defined as the maximum level of fault current which can be safely cleared.
  • It is the highest fault current that the MCCB can trip without being damaged permanently.
  • The MCCB will be reusable after interrupting a fault, as long as it doesn’t exceed this value.
  • It is indicate operation reliability of MCCB
  • This parameter may increase or decrease the cost, so it should be properly decided. Breaking capacity should be higher than the possible fault level. For domestic application fault level may be 10kA.

(4) Operating short-circuit breaking capacity (Ics):

  • It is expressed as a percentage ratio of Icu and tells you the maximum short-circuit current if a circuit breaker can break three times and still resume normal service.
  • The higher the lcs, the more reliable the circuit breaker
  • It is the maximum possible fault current that the MCCB can clear. If the fault current exceeds this value, the MCCB will be unable to trip and another protection mechanism must operate.
  • If a fault above the Ics but below the Icu occurs, the MCCB can interrupt it successfully but will need a replacement due to the damage suffered.
  • The Main difference between Ultimate Short Circuit (Icu) and Service Breaking Capacity (Ics) that Icu (Ultimate Braking Capacity) means Circuit breaker can remove the fault and remain usable but Ics (Service Braking Capacity) means Circuit breaker can remove the fault, but it may not be usable afterwards.
  • For example, if a circuit breaker has an Ics of 25,000 Amperes and an Icu of 40,000 Amperes:
  • Any fault below 25kA will be cleared with no problem.
  • A fault between 25kA and 40kA will cause permanent damage when cleared.
  • Any current exceeding 40 kA can’t be cleared by this breaker.

 (5) Rated working voltage (Ue):

  • It is the continuous operation voltage for which the MCCB is designed.
  • This value is typically equivalent or close to a standard system voltage.
  • In three phase it is usually 400V or 415 V. For single phase it is 230V or 240V.

(6) Rated Insulation voltage (Ui):

  • It is the maximum voltage that the MCCB can resist according to laboratory tests.
  • It is higher than the rated working voltage, in order to provide a margin of safety during field operation.

(7) Rated impulse withstands voltage (Uimp):

  • It is the value of transient peak voltage the circuit-breaker can withstand from switching surges or lighting strikes imposed on the supply.
  • This value characterizes the ability of the device to withstand transient over voltages such as lightning (standard impulse 1.2/50 μs).
  • Uimp = 8kV means Tested at 8 kV peak with 1.2/50μs impulse wave.

(8) Number of Poles:

  • No of Pole for MCCB depends on Single Phase & Three Phase Power Controlling /Protection
  • Single Pole (SP) MCB: 
  • A single pole MCB provides switching and protection for one single phase of a circuit.
  • Used: for Single Phase circuit
  • Double Pole (DP) MCB: 
  • A two Pole MCB provides switching and protection both for a phase and the neutral.
  • Used: for Single Phase circuit
  • Triple Pole (TP) MCB: 
  • A triple/three phase MCB provides switching and protection only to three phases of the circuit and not to the neutral.
  • Used: for Three Phase circuit
  • 3 Pole with Neutral (TPN (3P+N) MCB): 
  • A TPN MCB, has switching and protection to all three phases of circuit and additionally Neutral is also part of the MCB as a separate pole. However, Neutral pole is without any protection and can only be switched.
  • Used: for Three Phase circuit with Neutral
  • 4 Pole (4P) MCB: 
  • A 4 pole MCB is similar to TPN but additionally it also has protective release for the neutral pole. This MCB should be used in cases where there is possibility of high neutral current flow through the circuit as in cases of an unbalanced circuit.
  • Used: for Three Phase circuit with Neutral

What should you know before buying LED Bulbs (Part:3)

 (4) Color Rendering Index (CRI):

  • There are two standard measurements for the color characteristics of light: “color rendering index” (CRI) and “color temperature”, which expresses the color appearance of the light itself.
  • Color rendering index measures the ability of a light bulb to reproduce colors.
  • CRI is described How artificial light source is able to render the true color of objects as seen by natural outdoor sunlight which has a CRI of 100
  • The higher the CRI rating is, the better its color rendering ability.
  • Color Rendering Index (CRI) is a scale from 0 to 100.Incandescent bulbs are rated at 100 and most LED bulbs are usually rated somewhere between 80 and 85
  • CRI scoring of 100 is best and a CRI of zero being the worst.
  • CRI of 0: For a source like a low-pressure sodium vapor lamp, which is monochromatic compare to a source like an incandescent light bulb which has CRI of 100?
  • CRI of 62: A standard “cool white” fluorescent lamp will have a CRI near 62.
  • CRI of 70: Lamps with CRIs above 70 are typically used in office and living environments.
  • CRI of 82 to 86: Compact fluorescent lamps are graded at 82-86 CRI, which is considered high quality color rendering. CRI is a more important consideration for retail lighting design than it is for office lighting.
  • CRI of 80 and above: It is considered high and indicates that the source has good color properties.
  • Incandescent lamps and daylight have a CRI of 100, the highest possible CRI.
  • The higher the CRI of the light source, the “truer” it renders color.
  • The CRI can only be used to compare two light sources that have the same color temperature. A 5000 K, 80 CRI light source is not necessarily superior to a 4000 K, 70 CRI light source.
Color Rendering Index
Light source CRI
clear mercury 17
white deluxe mercury 45
warm white fluorescent tube 55
cool white fluorescent tube 65
deluxe warm white fluorescent 73
daylight fluorescent 79
metal halide 4200K 85
deluxe cool white fluorescent 86
metal halide 5400K 93
low pressure sodium 0-18
high pressure sodium 25
100-watt incandescent 100


Color Temperature & CRI
Lighting source Color Temperature Color Rendering Index
High Pressure Sodium Lamp 2100K 25
Incandescent Lamp 2700K 100
Tungsten Halogen Lamp 3200K 95
Tungsten Halogen Lamp 3200K 62
Clear Metal Halide Lamp 5500K 60
Natural Sun Light 5000K to 6000K 100
Day Light Bulb 6400K 80


Color Temperature & CRI
Kelvin Light Effect CCT CRI
Below 3600K Incandescent Fluorescent (IF) 2750 89
Below 3600K Deluxe warm white (WWX) 2900 82
Below 3600K Warm white (WW) 3000 52
3200K to 4000K White (W) 3450 57
3200K to 4000K Natural white (N) 3600 86
Above 4000 K Light white (LW) 4150 48
Above 4000 K Cool white (CW) 4200 62
Above 4000 K Daylight (D) 6300 76
Above 4000 K Deluxe Daylight (DX) 6500 88
Above 4000 K Sky white 8000 88

 (5) Beam angle:

  • How the light spreads out from the bulb (Beam Angle) is very important.
  • The beam angle determines how light is spread from the bulb into a given space.
  • The beam angle is the degree of width that light emanates from a light source. Specifically: The angle between those points on opposite sides of the beam axis where the intensity drops to 50% of maximum.
  • Typically a narrow beam angle is a ‘spot’ of light and called “Spot Light”. While a broader beam angle ‘floods’ with light, called a flood light. There are a number of much more specific designations of beam angle.
  • Beam angles of LEDs vary greatly and depend on their application. The shape of an LED bulb determines the direction light is emitted.
  • Narrow Spot Beam Angle: 05-15 degrees
  • Spot Beam Angle: 16-22 degrees
  • Narrow flood Beam Angle: 23-32 degrees
  • Flood Beam Angle: 33-45 degrees
  • Wide flood Beam Angle: 45+ degrees
  • Narrow angle bulbs less than 30 degrees are usually used when placing multiple down lights close to each other, such as in a hallway or when lighting cabinetry.
  • Larger beam angles are used with high-power LEDs for floodlighting. If you’re replacing incandescent or halogen lamps with LEDs, make sure the beam angle is similar to the old bulb.
  • Very large beam angles are sometimes found in pantries or walk-in wardrobes. As beam angle increases, we require more lumens (light output) to maintain the light’s intensity.


  (6) Efficacy (Lumen / Watt):

  • It is another important parameter to decide the performance of the LED bulb in terms of lumens.
  • It indicates effectiveness of the light bulb by converting electrical energy into visible light energy on watts used by Lighting Bulb; hence efficacy is total lumens per watt.
  • Example: 9W light bulb comes with lumens of 800 has an efficacy of 90 Lumens per Watt.
  • Incandescent bulbs give us light by passing electricity through a filament which heats up and emits light. In fact, 95% of the energy in these bulbs is lost to heat and only 5% is what produces light Hence, incandescent bulbs produce only 16 lumens / watt.
  • CFLs in the way they are built are more efficient and can give us between 50 to 70 lumens / watt (at least 3 times more than incandescent bulbs)
  • LED bulbs on the other hand, can output up to 100 lumens / watt – which make them one of the most efficient sources of lighting.
Parameter of LED Bulbs
Parameter Average Good Best
Lumens/Watt 75 90 100
Power Factor 0.7 0.8 0.9
CRI 60 70 80
LED Life in Hours 15000 25000 50000

 Other Technical Parameter:

(1) Instant Light:

  • LED Bulbs must be instant start and gives full Lumens from Starting.
  • When turning on CFLs and Fluorescent light bulbs, there is a slight hesitation before brightness is achieved, and some bulbs may flicker during warm up or even during operation.
  • Unlike fluorescents, LED bulbs, like incandescent bulbs, reach full illumination as soon as they are turned on.
  • LED lights produce a steady light which does not flicker.

(2) Dimming Capability:

  • Earlier versions of LED bulbs had the disadvantage of not being dimmable. Today, many LED bulbs are designed to work in dimmable switches which are provided in many lamps and home lighting fixtures.
  • Dimmable LEDs cost about 40% more than non-dimmable LEDs of similar wattage

(3) LED Driver:

  • The main cause of LED bulb failure is the driver. The driver is a small transformer that steps down the voltage from 230V AC to a much lower DC voltage for the LED.
  • It’s usually located inside the back of the bulb. A poor quality driver could result in bulb failure within months. The LED chip itself rarely fails until driver fails.

(4) LED Chip:

  • LED chips are manufactured by various big and small enterprises in the world. Some Good Suppliers make LED Chip of highest quality for longer life and more reliability.
  • Larger chip provide more lights, good stability against current variations, but it costs more.
  • Cheap and small led chip provides less light and stability. Ceramic COB lights are totally different in terms of size; they use multiple small chips to provide more lights and stability.

(5) Weight

  • LED lights need good heat dispassion, this can achieved by good amount of aluminum. Aluminum is generally used to provide better heat sink and extends the life of LED chip.
  • Thin heat sink can provide more area in less weight, but transfer enough heat for the removal.
  • Some lower quality products provide 12 to 20W lights in very low weight in plastic body. These products would not perform well even in small span of time.

(6) Heating:

  • Although LEDs don’t produce much heat they can overheat in operation if they’re not cooled correctly. Cheap LED’s are less efficient, produce more heat and are more heat sensitive. Operating above 60°C can damage cheaper LED’s shortening their life, reducing light output and efficiency. Generally the higher the wattage/power of a GU10 LED bulb, the more heat it produces requiring a more thermally efficient bulb body to keep the LEDs cool. Therefore beware of cheap higher wattage bulbs that don’t have a metallic or ceramic finned body. Another issue is that higher wattage thermally efficient LED bulbs may be so large that they are no longer a suitable size.
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