Low voltage- Short Circuit Specification
Low voltage- Short Circuit Specification
(OP)
My low voltage switchgear specifications says "Rated Short-Circuit Withstand Current: 25 kA rms for 3 cycles". Does this mean do I have to specify all the breakers (Incoming & Outgoing), bus bars with the same short circuit rating, that is 25kA rms,3 cycles.






RE: Low voltage- Short Circuit Specification
For example, if your ASCC is 8 kA, all components must be rated for 8 kA or greater.
Bill
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"Why not the best?"
Jimmy Carter
RE: Low voltage- Short Circuit Specification
" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden
RE: Low voltage- Short Circuit Specification
50 KVA, 240 Volt transformer. impedance Volts = 3.6%
FLC = 50000VA/240Vs = 208.3A
208.3A / .036imp = 5.787 kA
All devices must be rated in excess of 5.787 kA
A second calculation may be done to consider the impedance of the cable from the transformer to the switch gear. This will often drop the ASCC enough that 5 kA rated equipment may be used in this example.
For larger systems it may be necessary to consider also the grid Available Short Circuit Current.
Using the transformer impedance alone yields a worst case result.
Considering the grid capability may reduce the ASCC.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Low voltage- Short Circuit Specification
RE: Low voltage- Short Circuit Specification
EDMS Australia
RE: Low voltage- Short Circuit Specification