Importance of mcb : Will not save from over voltage ?

One of the most common mistake in wiring, we often confuse with MCB use for over voltage protection. After installation of MCB, the technician ensure us that our electrical circuit is safe from short circuit and other issues. We commonly thinks that this will also serve protection from other surges like over voltages etc. This phenomenon should not me mixed like this.

Over voltage is actually a certain condition when the voltage is higher than rated voltage for that particular circuit. In our domestic use, we have equipment having rating 230 V (phase to neutral) for normal operation. But it might shoot up at a higher rating from transformer. Generally, manufacturing company provide technical specification of each electrical apparatus. Let us have a common rating of “+” “-” 5% to 230 V means that this will imply below higher and lower acceptable rating for voltage

1.) Higher acceptable rating = 230V +5% = 241.5V

2.) Lower acceptable rating = 230V -5% = 218.5V

Now this equipment will run satisfactorily in rage of 218.5V to 241.5V. If voltage will be higher than 241.5V then it may damage. Now this voltage will be termed as over voltage for this equipment.

Protection from electrical faults, there are many terms are used in circuit like proper MCB,earthing, RCCB, ELCB etc. We should know basic working principle for proper information and safety.

Working principle of MCB and over voltage

MCB is actually a circuit breaker which cut off the circuit in case of higher current. It means that MCB will only sense current flowing from it. It is installed in series condition to do that.

In case of we have installed 32A triple pole MCB in circuit, then it will cut of the circuit either only current having higher rating tries to flow from it or in short circuit condition.

But we now confuse with Voltage rating of this MCB which shows 415V for three phase condition. Now we should be careful about its voltage rating which is not related to its tripping condition. But voltage is only for its satisfactorily working condition.

Now, question arise here what if voltage ig much higher than 415V for this MCB, will it protect the circuit from over voltage ?

Answer is NO, this higher voltage will change its thermal characteristics. As a result, MCB will not work properly and might trip for other current rating than it is designed for.

However electrical equipment are designed to sustain such spikes for short period and may produce much heat or other characteristics.