Powerpac Cable Sizing Software

Hi Guys,

I am using powerpac to size some cables which uses australian standards to do so. When specifying the load details on a cable, it has some fields which relate to short circuit. My understanding of these fields are:

Fault clearing time (secs): How long the relay and/or circuit breaker takes to clear the fault, lets say 1 second for this example.

Trip Multiplier: What the instantaneous setting as a multiple of over current pick up for over current is on the breaker, lets say its 2.

Let through energy I^2t: This is calculated automatically by powerpac, for this example of with a 3000A breaker present, it comes up with a let through of: 43560000

How does it come up with that answer?