Large loss of PSCC across first leg of circuit from Transformer to Main switchboard

Question

Afternoon all 
 I hope someone can shed some light on what i think is a problem with hevacomp connect, i am currently working on a large project and at the transformer, we have a fault current of 24kA but 10m upstream we have a fault current of 7.9kA so losing 17kA through 3 no. 185mm2 SWA cables. 
 I thought this may have simply been an error on this project due to entering something incorrectly but a colleague checked a calc they produced and the same happens, it seems the board downstream will let nothing more than 3kA through. 
 
 I have tried changing the protective device and this changes nothing on the fault current which remains at 7.9kA. 
 
 Any ideas / help would be greatly appreciated. 
 
 Andy

Duncan Brown · Accepted Answer

Andy - you have used current limiting devices in the circuit (Schneider Compact NSX MCCB + Micrologic 2) - Under fault conditions, the current is limited. This document contains a little more information. In the example circuit, for example, the device on MSB/SA way 3 is an NSX400 N 2.3 50kA. If you examine the device data, you can see that the let through energy is going to be between (I haven't interpolated the figure exactly) 6 and 7kA.

Large loss of PSCC across first leg of circuit from Transformer to Main switchboard

Top Replies