Types and accessories of MCB/MCCB

 

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

MCB trip curves

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.

MCB/MCCB Accessories:
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
Shunt Trip:
  • Used for Remote Tripping
Alarm contact:
  • It gives Tripping Indication when MCCB Trip.
  • It does not give when MCCB is in normal condition (either ON or OFF)
Auxiliary contact:
  • It used for remote signaling and control purpose.
  • It is also give ON/OFF indication of MCCB at remote location.
Under Voltage Tripping:
  • It used to trip MCCB in under voltage condition (70 to 35% of rated Voltage).
Mechanical Interlocking:
  • It used to mechanical interlock of two MCCB on the same Panel.
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
Motorized operation:
  • MCCB may have option for manual operation or with a motor mechanism for electrically controlled
Others:
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.

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.

Type of Mounting Arrangement:

According to mounting arrangement, MCBs can be divided into two categories.

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.
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.
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.
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