“MCB “stands for Miniature circuit breaker. These circuit breakers provide protection from “overload “and “short circuit” conditions. MCB are available up to 125 Amps, Further above there are MCCB.
MCCB
MCCB stands for “molded case circuit breaker“. It is a type of evolve version of MCB (Miniature circuit breaker). MCCB contains a single operating knob unlike the MCB (MCB is having a combined knob) Which is been utilized to change the state position of MCCB.
MCCB are more bulkier and heavier in size compare to MCB. MCB provides protection for up to 125 Amps while MCCB provides protection for up to 2500Amps. MCCB are available in “single pole” , “double pole“, “three poles” , “four poles” and “five poles” types.
MCCB is having 3 state positions :
- Connected state – At this state, Both the sides are connected. Operating knob stays at uplift position.
- Disconnected state – At this state, Both the sides are disconnected. Operating knob stays at downward position.
- Trip state– Both the states are disconnected. This can be achieved either through tripping from short circuit or overload condition or This state can be achieved through trip button present on MCCB. At trip state, Operating knob stays at intermediate state in between connected and disconnected state.
Normally, MCCB have “line “and “load “terminals are distinguished. In Some MCCB, There is no fixed positioning of line and load. Line and loads can be connected any where.
Working principle of MCCB
MCCB provides protection from “Overload ” and “short circuit ” conditions. “Overload “is slow process phenomenon where high current more than MCCB rated current flows for long time at slow rate. While “short circuit” is rapid process phenomenon Where heavy current multiple times higher than the MCCB rated current.
MCCB works on 2 phenomenons :
- Microprocessor based
- Thermal-magnetic tripping
Since both are different phenomenon, There are two different trip mechanisms working .
- “Thermal and magnetic tripping” works on mechanical arrangement. For overload protection, thermal tripping works. For short circuit protection, Electromagnet tripping works. Both the phenomenon are working on one common goad of tripping.
Thermal tripping contains bimetallic element which get bend when current exceeds the limit due to heat. That bending movement is utilized in trip the circuit.
Electromagnet tripping contains an solenoid coil Which contains a metallic rod in between. When short circuit happens due to rapid heavy current coil becomes electromagnet and pull the metallic rod. That movement of metallic rod is utilized to trip the circuit.
- Microprocessor based MCCB contains microprocessor and digital system. Microprocessor continuously monitors the Present parameters. According to the stored program and present parameters, Microprocessor provides the tripping signal.
Tripping is usually a protective action, not necessarily a fault in the MCCB itself. Every single tripping is important which should not be ignored.
Difference in between MCB and MCCB
| PARTICULARS | MCCB | MCB |
| Full form | Molded case circuit breaker | Miniature circuit breaker |
| Current Rating | Higher current rating capacity up to 2500Amps | Low current rating up to 125 Amps. |
| Trip setting adjustment | Possible | not possible |
| External handle (External operation) | Possible | not possible |
| Size | bigger | Smaller |
| Weight | Heavier | lighter |
| Trip Button | Available | Not available |
| Special trip position | Yes | No, deenergized state is the trip state |
Description marked on MCCB
“The rated current “In “is actually the current level up to which MCCB work normally without getting tripped. MCCB follows the inverse time characteristics for tripping, Higher the fault current, Rapid will be the tripping.”
MCCB are designed to protect the circuit from “overload “and “short circuit” conditions. During fault situation, Fault current can go beyond multiple times higher than the rated current. That’s why MCCB are designed to bear that much high current much more than its rated current.
Apart from “In “rated current, There are several other current parameters are mentioned such as “Icu “and “Ics“.
- Icu : It is the maximum current level at which MCCB can interrupt only once without getting being exploded on leaked. After that MCCB may not be able to work further. Icu stands for “ultimate short circuit current capacity“. Icu is expressed in KA(KILO AMPS).
- Ics : It is the current level which MCCB safely interrupt and remains operational after that current limit. The distribution design entirely depend upon these short circuit current ratings. Ics stands for “service short circuit current capacity“. Ics is expressed as percentage of Icu rating.
Likes those current parameters, There are other several parameters marked on MCCB. For better understanding DN3-630D MCCB model by L&T is discussed through a table below :
| PARTICULARS/PARAMETERS | DESCRIPTION | REMARKS/PARAMETERS VALUE |
| Icu | Maximum current level which MCCB can interrupt only once without getting being exploded or leaked. After that level, MCCB may not remains operational. | Represented in KA. 36KA |
| Ics | The current level; MCCB safely interrupt and remains operational after that current level. | Expressed as % of Icu. 100% |
| CAT | Category defines when fault time delay exist or not . | A category breakers are required where downstream discrimination with another circuit breaker under short circuit condition; is not required. It do not contains time delay for short circuit condition. CAT A is Ideal for general power distribution. |
| Uimp | Impulse withstand voltage | Generally expressed in KV. 8KV |
| Ue | Rated operational voltage | 415/440 V |
| Frequency | Supply frequency | 50Hz/60Hz |
| Make : Logo | L&T | |
| Model/Frame size | DN3-630D | |
| Standards | Following the rules by made by governing body | IS/IEC 60947-2 | EN 60947-2 |
| Working type | Based on working mechanism Such as electromagnetic tripping and microprocessor based tripping | Thermal magnetic Release |
Type of MCCB
Type of MCCB based on breaking capacities
Ranges from 10KA to 100KA such as :
- 25KAmps
- 36Kamps
- 50Kamps
Type of MCCB based on pole
- Single pole
- double pole
- three pole
- four pole
- Five pole
Type of MCCB based on trip mechanism
- Microprocessor Based
- Thermal-magnetic tripping
Application of usage of MCCB
- For power distribution
- For motor protection
- Switch disconnector
- DC powereḍ
- Capacitor duty heavy circuits
Frequently Asked Questions (FAQs) related to MCCB
1. What is an MCCB?
MCCB stands for Molded Case Circuit Breaker. It is a low-voltage circuit protection device used to protect electrical circuits and equipment against overload and short-circuit faults. Depending on the model, an MCCB may also provide earth-fault protection and other advanced functions.
2. How does an MCCB work?
An MCCB continuously monitors the current flowing through the circuit. When an overload or short circuit occurs, its trip mechanism operates and opens the contacts, disconnecting the faulty circuit. Thermal-magnetic or electronic trip units are commonly used for protection.
3. What is the difference between MCB and MCCB?
The main differences are current rating, breaking capacity, adjustability and application. MCBs are generally used for smaller electrical circuits, while MCCBs are commonly used in industrial and commercial systems where higher current ratings, greater fault-breaking capacity and adjustable protection may be required.
4. What are the types of MCCB?
The main types of MCCBs include thermal-magnetic MCCBs and electronic MCCBs. MCCBs can also be classified according to their number of poles, current rating, breaking capacity and available protection functions.
5. What is the breaking capacity of an MCCB?
The breaking capacity of an MCCB is the maximum short-circuit current that the breaker can safely interrupt at its specified voltage and under specified test conditions. It is generally expressed in kA (kiloamperes).
6. What are Icu and Ics in MCCB?
Icu is the rated ultimate short-circuit breaking capacity, while Ics is the rated service short-circuit breaking capacity. These ratings indicate the MCCB’s short-circuit interruption capability according to the applicable standard and test conditions.
7. How do I select the correct MCCB?
MCCB selection should consider load current, system voltage, number of poles, cable ampacity, prospective short-circuit current, breaking capacity, trip characteristics and protection requirements. The selected MCCB should coordinate correctly with the cable and other protective devices.
8. Can an MCCB protect against overload and short circuit?
Yes. MCCBs are designed to provide overload and short circuit protection. Thermal or electronic protection generally handles overload conditions, while magnetic or electronic instantaneous protection responds to high short-circuit currents.
9. What is the difference between thermal-magnetic and electronic MCCB?
A thermal-magnetic MCCB uses thermal and magnetic protection mechanisms, whereas an electronic MCCB uses an electronic trip unit to measure current and control tripping. Electronic MCCBs generally provide greater adjustment and additional protection functions.
10. What is the difference between MCCB and ACB?
An MCCB is generally used for low-voltage circuit protection in feeders, distribution boards and industrial applications. An ACB (Air Circuit Breaker) is commonly used for higher-current applications such as main incomers and large distribution systems and typically provides more advanced protection and control features.
11. Why does an MCCB trip?
An MCCB can trip because of overload, short circuit, earth fault or incorrect protection settings, depending on its design. The cause of the trip should be identified before resetting the breaker, especially when repeated tripping occurs.
12. What are the important specifications of an MCCB?
Important MCCB specifications include rated current, rated voltage, number of poles, breaking capacity (Icu/Ics), trip unit type, protection settings, frequency and insulation-related ratings. Always check the manufacturer’s datasheet for the exact model before selecting an MCCB.
13. Where are MCCBs used?
MCCBs are widely used in industrial control panels, commercial buildings, distribution boards, motor control panels, generator panels, transformer incomers and other low-voltage power distribution systems where higher current and short-circuit protection are required.