Determining the energy let through of cable and protective device

 To get the let-through energy value of a particular breaker, you need to follow these steps:

1. Determine the maximum short-circuit current at the breaker.
2. Determine the protection tripping time of the breaker.
3. Calculate the let-through energy using the formula I²t = (k² x S²) / t, where k is the thermal constant, S is the cross-sectional area of the conductor, and t is the protection tripping time.

Here is an example of how to calculate the let-through energy value of an ABB SACE rated 63A breaker:

1. The maximum short-circuit current at the breaker is 50 kA.
2. The protection tripping time of the breaker is 0.1 seconds.
3. The thermal constant k for copper is 115, and the cross-sectional area S of a 63A breaker is 16 mm². Therefore, the let-through energy value of the breaker is:

I²t = (115² x 16²) / 0.1 = 2,174,400 A²sSo, the let-through energy value of an ABB SACE rated 63A breaker is 2,174,400 A²s.