SELECTION OF MCCB / MCB (LESSON-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 |
 |  |
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 |