Tripping of ABB S251 6A Type 2 M6 240/415V Circuit Breaker

I have a ABB S251 6A Type 2 M6 240/415V Circuit Breaker in power panel at my home. I have observed that only this circuit breaker trips whenever there only a slight rain. NO other circuit breaker in the panel trips. The is no dripping of rain water into the panel. Can somebody guide what is happening?

Masood Alam said:

I have a ABB S251 6A Type 2 M6 240/415V Circuit Breaker in power panel at my home. I have observed that only this circuit breaker trips whenever there only a slight rain. NO other circuit breaker in the panel trips. The is no dripping of rain water into the panel. Can somebody guide what is happening?

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The device concerned seems to be a simple miniature "Circuit Breaker" rated at 6 A (for a "Lighting" circuit.)
It is designed to "trip" whenever the loading on the circuit concerned "significantly" exceeds its rated carrying capacity of 6 A.
(It is not a RCD, RCBO, or GFCI - designed to detect Earth leakage.)

From this, one might conclude that there is rain water penetrating the building concerned which is then affecting the wiring connected to this protection device.
This device is protecting the wiring connected to it from "overload".
(Were the wiring not so protected you could have a serious problem - possibly, resulting in a fire.)

You must find where this water is penetrating the building and affecting the circuit concerned.

another probable cause is that there is an external light fitting or switch (or even an external fitting that is not a lamp, such as a TV aerial amplifier)