Short circuit current rating conversion

[mohammadfawaz]

Hey all!
An equipment is rated for 31.5kA short circuit fault current for 3s.
How can I know how much fault current it can withstand during 1s fault?
thanx

 

[jim dungar]

There is no simple way.
If you know the actual test procedures used to created the 3s test, you may be able to determine the 1s values.

You really need to ask the manufacturer.

 

[mohammadfawaz]

well, after researching IEC standards, I found the following in IEC 61439:
"For times up to a maximum of 3 s, the relationship between the rated short-time current and the associated duration is given by the formula I2t = constant , provided that the peak value does not exceed the rated peak withstand current."
I think I'm going with that formula.
what do u think?
thanx.