how to find KA rating including all factors in copper..

You can use ETAP short circuit simulation for more accurate.

thanks for your reply but i need theoritically calculating formulas.

CHECK COPPER.ORG

Refer copper development association

Dear Selvarengan ;

Please let me what exactly you want to know about KA in Copper, as your question is not too clear

Dear sir
I want to know the maximum current withstanding capacity formula for copper, so i mentioned it should consider all factors like temperature etc.

Cable manufactures too give it.

yes, cable manufacture have the short circuit damage curve for the conductors that they make.

I want that formula cause I'm using copper bars

Please consult the manufacturer of copper bars.

Dear ;

The flowing of a short circuit current in cable provokes a " Thermal Stress ", so, 2 factors affect the cables, that are :

1- The value of the Short Circuit Current " Isc "
2- The flowing time of that current " t "

We can, by using the following formula, calculate the withstand time :

Isc^2 * t <= K^2 * S^2

Where :
S : section of cable
K : factor relative to the cable's material " Cu or Alu " and the insulation's material " PVC or XLPE ", where the approximate values are :
- K = 115 : for " Cu & PVC "
- K = 76 : for " Alu & PVC "
- K = 143 : for " Cu & XLPE "
- K = 94 : for " Alu & XLPE "

Noting that the " IEC " defined the maximum time of withstand by " tmax : 5 sec "

which is safer 1sec or 5sec

5 sec only sir

Refer to the NEC tables for the standard ratings of conductors at a normal ambient temperature of 40C. The NEC includes tables for current adjustment for higher temperatures, conductor density and spacing within a raceway, There are also factors to be considered for underground duct banks, location within a duct bank, etc.. For high voltage conductors refer to the NESC as well as the manufacturer tables for a specific conductor size, insulation, conductor material. conductor configuration, etc. The basic formulas are within the NEC.

Dears ;

First, certainly the safer is " 5 sec ", because we can remark from the formula mentioned in my previous comment that as " t " is increased the cable's section will be increased.

Yes, it's only " 5 sec ", because this time's value is too bigger than the tripping time of any low voltage circuit breaker even with the maximum timing delay.