LV switch board short circuit rating
LV switch board short circuit rating
(OP)
Good day to you
We are planning to add a Sub switch board (415V)using 800Amps ACB feeder from a main LV switch board of 4000Amps, 65kA 1 sec.
The sub switch board(800A) will be located about 300mts from the main Switch board and connected using 3 runs of 630Sqmm Cable. The consultant is suggesting short time rating for the switch board as 25kAmos for 1 sec. Consultant says it is reduced due to cable impedence. Will it be enough? All our existing sub switch boards in the old plant are rated for the same main switch board rating of 65kA 1 sec irrespective of distance from the main switch board.
It will be helpful if any of you can advise whether we can accept the new sub switch board with lower Short time rating.
Thanks in advance.
We are planning to add a Sub switch board (415V)using 800Amps ACB feeder from a main LV switch board of 4000Amps, 65kA 1 sec.
The sub switch board(800A) will be located about 300mts from the main Switch board and connected using 3 runs of 630Sqmm Cable. The consultant is suggesting short time rating for the switch board as 25kAmos for 1 sec. Consultant says it is reduced due to cable impedence. Will it be enough? All our existing sub switch boards in the old plant are rated for the same main switch board rating of 65kA 1 sec irrespective of distance from the main switch board.
It will be helpful if any of you can advise whether we can accept the new sub switch board with lower Short time rating.
Thanks in advance.






RE: LV switch board short circuit rating
Is that three 630sq mm per phase? That seems excessive for 800 amps.
RE: LV switch board short circuit rating
Regards
RE: LV switch board short circuit rating
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If we learn from our mistakes I'm getting a great education!
RE: LV switch board short circuit rating
RE: LV switch board short circuit rating
Sometimes it's better to use more smaller conductors. Two 250 sq mm copper (is yours copper or aluminum) per phase would be about 7.5% for 800 amps at 85% pf. It would take five 250 sq mm to get 3%. For 500 sq mm, you would still need four per phase for 3%.