Trip Test for MCBs taking more time

[mirriyaz]

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.

 

[chuckey]

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

 

[Orson Cart]

the starting temp of the MCB will affect the time taken