Why is the backup more reliable than the MCB

Circuit breaker or automatic circuit breaker

What is MCB?

Nowadays we use more often Circuit breaker or MCB in the low-voltage network instead of the fuse.
The MCB has some advantages over backup.
  1. It automatically switches off the circuit if the network medium is in an overloaded state or in a faulty state. But the fuse does not feel Circuit breaker does it in a more reliable way. MCB is much more sensitive to overcurrent than fuse.
  2. Another benefit is how the switch works, with the button in the off position during triggering, the faulty area of ​​the circuit can be easily identified. In the event of a fuse, however, the fuse wire should be checked by opening the fuse handle or a cutout from the fuse base to confirm that the fuse wire has broken through.
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  4. A quick restoration of the supply may not be possible in the event of a backup, since the backups must be restored for the restoration of the supply. With MCB, however, a quick recovery is possible by simply switching on.
  5. Handling MCB is electrically safer than fuse. Due to the many advantages of MCB compared to fuse units, a line circuit breaker is usually used in modern low-voltage networks instead of an outdated fuse unit.
The only disadvantage of MCB over backup is that this system is more expensive than the backup unit system.
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Circuit breaker or automatic circuit breaker
Working principle of the residual current circuit breaker ELCB | Voltage and current ELCB | RCCB

Functional principle of miniature circuit breaker

There are two arrangements of Operation of the circuit breaker. One due to the thermal effect of overcurrent and the other due to the electromagnetic effect of overcurrent. The thermal Operation of the circuit breaker is always achieved with a bimetal strip A continuous overcurrent flows through MCB, the bimetal strip is heated and deflected by bending. This bending of the bimetal strip releases a mechanical lock. Since this mechanical lock is connected to an actuation mechanism, the contacts of the circuit breaker are opened.

In the event of a short circuit, however, a sudden increase causes an electromechanical displacement of the piston in connection with the trip coil or the solenoid valve of the MCB. The piston strikes the release lever and causes the locking mechanism to be released immediately Circuit breaker Contacts This was a simple statement from Functional principle of the miniature circuit breaker.

Miniature circuit breaker design

Circuit breaker construction is very simple, robust and maintenance-free. In general, an MCB is not repaired or serviced, but simply replaced with a new one when necessary. A circuit breaker usually has three main components. These are:

Frame of the circuit breaker

The frame of the circuit breaker is a molded housing. This is a rigid, strong, insulated housing in which the other components are mounted.

Operating mechanism of the circuit breaker

The operating mechanism of the miniature circuit breaker allows manual opening and closing of the miniature circuit breaker. It has three positions "ON", "OFF" and "TRIPPED". The external switching interlock can be in the "TRIPPED" position if the circuit breaker is triggered due to overcurrent. If you switch off the MCB manually, the switching bolt is in the "OFF" position. When the MCB is closed, the switch is in the "ON" position. By observing the positions of the pawl, you can determine whether the MCB is closed, triggered or manually switched off.

Trip unit of the line circuit breaker

The trigger is the main part responsible for its proper function Working of the circuit breaker. There are two main types of trigger mechanisms in MCB. A bimetal offers protection against overload current and an electromagnet protects against short-circuit current.

Operation of the circuit breaker

There are three mechanisms in a single circuit breaker for shutdown. If we carefully look at the adjacent picture, we will mainly find a bimetal strap, a trip coil and a hand lever to turn it on and off. The electrical current path of a circuit breaker shown in the figure is as follows. First the left power terminal - then the bimetal strip -, then the current coil or the trip coil - then the moving contact - then the fixed contact and - on the right the side current terminal. All are arranged in series.
If the circuit is overloaded for a long time, metal tape will overheat and deform. This deformation of the bimetal strip causes a shift in the locking point. The movable contact of the MCB is arranged by means of spring pressure in such a way that at this locking point a slight displacement of the bolt causes the spring to be released and causes the movable contact to move to open the MCB. The current coil or trip coil is arranged so that during a short circuit fault, the mmf of that coil will cause the piston to hit the same stop point and cause the shutter to slide. Therefore, the MCB opens in the same way. Again when operating the lever Circuit breaker is operated by hand, that is, if we do that, when the MCB is in the off position manually, the same locking point is shifted as the moving contact separates from the fixed contact in the same way. Whatever the actuation mechanism, that is, it may be due to a deformation of the bimetal strip, an increased mmf of the trip coil, or manual actuation, in fact the same locking point is shifted and the same deformed spring is released that is ultimately responsible for movement of the moving contact are responsible. If the moving contact is separated from the fixed contact, there is a high possibility of arcing. This arch then goes up through the arch runner and penetrates arch dividers and is eventually erased. When we turn on an MCB, we actually reset the shifted operating interlock to its previous on position and make the MCB ready for another turn-off or trip operation.

Video editing by MCB