I was performing Trip Test for MCB inisde my meterign panel. I was testing a 2-Pole AC MCB rated 6A, now I was injecting 12A of AC current & as per the Tripping curve of C type MCB it should've tripped in 15 seconds approximately (I believe so) but its taking around 25 seconds that too after testing it for more than two times.
Can't think what the problem is , I thought the springs in MCBs get weak with age and use and they trip quicker. I had a look at some curves ( **broken link removed** ), It seems that all types have the same tripping characteristics for small overloads but different for high current overloads.
Frank