Short Circuit Rating of Cable

What does the characteristic curve of the circuit overload protective device look like?

I agree, of course, with jack.

You have to recalculate the short-circuit current at the end of the cable. The resistance and the reactance of the cable could reduce the current dramatically.

Second, usually 0.1 sec it is enough time to clear the short circuit.

If the cable is XLPE or EPR insulated the maximum temperature it is 250 deg.C.

If you need to take into consideration a reserve protection 0.15-0.2 sec still will be fair.

For 0.15 sec [for adiabatic phenomenon] 250 MCM at 40 KA [rms] will be the minimum copper cross section.

Beware, 0,1 sec seems a bit short . It depends on your protection scheme, this time may be mich longer specially in MV where you have time discrimination.

I agree with you, obouill, it is very short, but 5 cycles [total] clearing fault it is still possible.

It is depend on your design philosophy.

1. primary protection tripping time (relay 50/51 of outgoing feeder)

2. secondary protection tripping time (relay 50/51 of main breaker)

If you are a good engineer with money to invest, choose cable to tolerate SC time in 2.

If you are on budget, choose cable rating of SC time in 1.

Now you know what I mean.

"Now you know what I mean." No?

I agree with Jack.

But also the cable manufacturer catalog shall give to you a curve showing the maximum admisible sc againt time in sec., ask for this information.

Bye ( now definitive becouse tomorro I lose the computer and internet, Chaoooo Dear friends)