Question

How is M.C.B. superior to the fuse wire?

Answer 1

Hint: A miniature circuit breaker (M.C.B.) is an electromagnetic device with a fully molded insulating material. This device's primary function is to switch the circuit. This means that when the current passing through the circuit exceeds a predetermined value or limit, the circuit (which is connected to it) will automatically open. The device, like any other switch, can be turned on and off manually.

Complete answer:
MCBs are time-delay tripping circuit breakers. The operating time of these devices is controlled by the magnitude of the overcurrent passing through them, which means that the device operates whenever an overload exists for long enough to endanger the circuit being protected.

Transients such as motor starting currents or switch surges do not affect MCBs. These devices are typically designed to operate in less than 2.5 milliseconds when there is a short circuit fault and between 2 seconds and 2 minutes when there is an overload.Under normal operating conditions, the MCB acts as a switch (a manual switch) to turn the circuit on or off.

The device automatically trips in the event of a short circuit or overload. This will cause a current interruption in the load circuit, resolving the issue. The trip is visually indicated as the operating knob automatically moves to the OFF position. The automatic operation/ tripping MCB can be obtained in two ways; magnetic tripping and thermal tripping.

When there is an excessive flow of electric current in a circuit, the M.C.B. automatically falls and switches off the circuit in a very short time. It is raised after the fault has been corrected. M.C.B.s do not need to be replaced every time a high current passes through them, but fuses must be replaced because they melt and break. Thus, in this way M.C.B is superior to the fuse wire.

Note: In most cases, MCBs used in domestic installations are rated at 6kA or 6000 amps. Because of the relationship between normal voltage (240v) and typical household appliance power ratings, the over-current caused by a short circuit should not exceed 6000 amps. However, when using 415v and large machinery in commercial and industrial settings, 10kA rated MCBs are required. These rankings represent the maximum Prospective Fault Current (PFC) that the MCB can withstand and still operate correctly by disconnecting the circuit. Should the PFC be exceeded, the MCB could fail to result in the contacts welding shut.