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
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