Why buy Miniature Circuit Breaker?
What is MCB?
Miniature Circuit Breakers (MCB) is the more efficient and updated versions of an electrical fuse. Similar to the fuse it is a device that protects the circuit from over-current. The key difference is this: a fuse functions as a ‘sacrificial device’, i.e., the wire or metal strip inside it melts to protect the circuit. This renders it unusable afterward whereas an MCB detects any excess current and breaks the circuit. This is reflected in the tripping of the MCB. Unlike fuses, MCB can be reused even after it trips.
They are much easier to use, offering the convenience of ‘on/off switching’ for circuit isolation and since the conductor is housed within a plastic casing, they are much safer to use and operate. However, MCBs do not protect human beings from the electrical shock caused by ‘earth leakage’; that is ensured by RCCB (residual current circuit breaker) and RCBO (residual current breaker operator). A wide variety of MCBs has been in use nowadays with a breaking capacity of 10KA to 16 KA, in all areas of domestic, commercial, and industrial applications as a reliable means of protection.
How Does It Work?
z. Incoming Terminal
6. Arc Chutes Holder
7. Arc Chutes
8. Dynamic Contact
9. Fixed Contact
10. Din Rail Holder
11. Outgoing Terminal
12. Bi-metallic Strip Carrier
13. Bi-metallic Strip
An MCB provides protection from both overload and short circuit. Since these two types of over-current manifest in very different ways, an MCB detects and then
deals with them differently: 1) Thermal operation& 2) Electromagnetic operation.
Overload protection is provided by the bimetallic strip around which a heater coil is wounded to create heat depending on the flow of current. Bimetallic strips are chosen to provide particular time delays under certain overloads. They are usually made of two types of metal, brass, and steel. During slow continuous over-current, characteristic to overload, the bimetallic strip is heated by the electrical charge and thus bends, releasing the mechanical latch. The latch, which is connected to the operating mechanism causes the contacts to open and breaks the circuit.
If a short circuit occurs, the huge surge in electrical current causes the displacement of the plunger from the solenoid, striking the trip lever, thus breaking the circuit.
MCBs can be switched ON and OFF manually. This functionality is highly useful, especially during maintenance. The operation of MCBs is affected by environmental temperature, particularly the deflection of the bimetallic strip. Hence it is very important to choose appropriate MCB based on its ambient temperature.
MCBs may be of single, two, three, or four-pole versions. In two, three, and four-pole versions, the respective number of single poles MCBs are joined together and their knobs are combined so that fault cleared by anyone of the poles will open all the poles together.
Diagram showing the Thermal trip arrangement
Tripping Curve of an MCB:-
The Tripping Curve of an MCB allows for the real-world and sometimes entirely necessary, surges in power. In commercial environments, for example, large machines usually require an initial surge of power in excess of their normal running current to overcome the inertia of large motors. This brief surge lasting just a few moments is allowed by the MCB as it is safe to do so for this very short amount of time.
MCBs are categorized into three major types based on their tripping curves-
- Type B-This kind of MCB is used in domestic or very light commercial establishments where the surge of power is limited. The MCBs trip between 3 and 5 times full load current, so a 6amp MCB with a B curve will trip between 18a and 30a, depending on how long the over-current lasts, but roughly between 10 and 8 seconds.
- Type C-These are normally used for high inductive loads where switching surges are high such as small motors and fluorescent lighting. They are able to trip five to ten times its rated current.
- Type D-These trip instantly from ten to twenty-five times and are used in heavy industrial facilities such as factories using large winding motors, X-ray machines, or compressors.
All the aforementioned MCBs provide surge protection within one-tenth of a second… The minimum and maximum trip currents of these MCBs are given below. Here is the rated current on the MCB.
Diagram showing Magnetic trip arrangement
|MCB||MINIMUM TRIP CURRENT||MAXIMUM TRIP CURRENT|
Uses for domestic MCBs-
Whilst every installation is different and should always be designed by the fully qualified professional electrician on site, there are some standards which most domestic wiring schemes adhere to:
6 Amp – standard lighting circuits
10 Amp – large lighting circuits – though these are becoming rarer in domestic settings as technology and trends move towards lower energy lighting sources such as LED.
16 Amp and 20 Amp – Depending on the power rating these are both commonly used for immersion heaters and boilers
32 Amp – Ring Final; the technical term for your power circuit or sockets.
40 Amp – Cookers / electric hobs / small showers
50 Amp – 10kw Electric showers / Hot tubs.
Tripping of MCB and potential faults
An MCB might trip whenever there’s a brief circuit, overload, or maybe once they square measure being ‘underrated’, within the sense that the ampere rating of the breaker isn’t properly chosen. the explanation for tripping ought to be known and faults should be cleared before turning ON them once more. When it visits, 1st of all, we’ve to ascertain whether or not there square measure any visible faults like short circuits or overloads.
Even amalgamate LED lamps will trip Associate in Nursing MCB. If there’s no visible fault within the circuit protected by it, wait until it cools down and switch it ON once more. If it visits once more directly, which means there’s a brief circuit within the circuit or instrumentation it protects. If it visits once more once some minutes, then there’s an opportunity that the circuit or instrumentation is full. Clear the fault within the instrumentation OR gate and switch on the MCB. provoke knowledgeable recommendations if needed.
Advantages of victimization Associate in Nursing MCB over Associate in Nursing electrical fuse:-
- Miniature Circuit Breakers will act quicker than fuses (2-3.5ms) throughout short circuits.
- Supply higher overload protection than fuses.
- May be reset once the clearance of fault. However, fuses got to be rewired or replaced
- Safer interruption of short-circuit current and arc termination.
- The knob makes the operation of a miniature electrical fuse abundant easier than a fuse.
- They may be turned off whenever we would like. Therefore, Circuit isolation throughout maintenance is far easier compared to fuses.