MCB trips when bulb blows.

[Extrasolar]

If a bulb blows when I turn on a light the MCB trips. Why is this? Is it because of the speed in which the bulb blows? Or a surge?

 

[breezer]

when a lamp fails it is because the filament usually breaks. for the sake of argument the filament is 4 foot long everything is ok, when you turn on the lamp the filament breaks in its weak spot, say1 foot from the end, that leaves 3 feet, this 3 feet moves with the reaction when the element breaks, the 3 feet bit then touches another part of the remaining 1 foot, at say 6 inches. this now means that instead of being 4 feet long the element is now 3 feet 6 inches, this in turn means that what was bright and drew X amount of current is now even brighter and draws XX amount of current ( a lot more than it used to) this current is so much that the mcb can not supply this amount of current so it trips.

If you watch carefully and are quick enough you will see the lamp flash very brightly when it does this.

If the element does not do the above and break then the lamp just does not iluminate and and the mcb does not trip.