I have a Murray 400 amp service panel. The Short Circuit Current Rating is 20,000AMPs. I need to know the Short Circuit Interrupting Rating. Can anyone help?

The short circuit interrupting rating of any circuit breaker installed in that panel cannot exceed the 20kA rating of the panel.

A panel, or any equipment that will contain a fuse or circuit breaker will have a Short Circuit Current Rating.

A protective device, such as a fuse or circuit breaker will have a Short Circuit Interrupting Rating.

Before you decide that the 400 amp panel you have chosen is of the proper short circuit rating, a short circuit coordination study must be done.

To see what is involved, here is as simple as an explanation I can find, this is not for a DIY. If you're an electrician, you should know this process.

http://www.cooperindustries.com/content/dam/public/bussmann/Electrical/Resources/Solution%20Center/technical_library/BUS_Ele_Tech_Lib_Short_Circuit_Current_Calculation s.pdf

I have a Murray 400 amp service panel. The Short Circuit Current Rating is 20,000AMPs. I need to know the Short Circuit Interrupting Rating. Can anyone help?
May I ask WHY you need to know this?