My project has an LV supply fed via a sub-station with an outgoing 800A fuse. The supply is 90m and connects to a panel board with an incoming 630A MCCB.
The earth sizing is currently calculated at 2x185mm2 cables in parallel. When I fix this to a single cable of 400mm2 CSA the disconnection time is not achieved and the circuit fails. When connect is left to calculate on a single earth the 630mm2 cable is still not sufficient.
Having carried out a check adiabatic calc using the values of I2t in the model, and with fuse data, the 400mm2 earth is more than sufficient. And as this exceeds the total CSA of 2x185mm2 cables should be sufficient in the model to clear the fault in under 5 seconds.
Can you please some commentary on the above sizing.
Thanks
Stuart O'Loughlin
Duncan,
Files uploaded as requested.
Stuart
Yes Duncan,
I included the 2 custom cable types and the newcab.ndx file in the root of the zip.
Thanks, Stuart - I've got that now. I can see why this might be causing concern. It does seem to be working backwards. I shall have to get into the code and see what's happening.Regards,
Duncan Brown
Hi Stuart - You haven't been forgotten - in fact you have been my priority all day...the software appears to be generating a very low resistance for parallel cpc's. I need to do a little more research into this. I will be back as soon as I have more information.Regards,
Its been sometime since I last herd from you.
Can you give me an update on this please.
Hi StuartThe reactive component of the CPC is very low in all these cases, and you also consider that in the case of parallel CPC's, the reactance used is one-half the reactance of a single cable. As the reactive component changes very little in these cases, they will generate a fail at 400mm2See the attached for more details.Regards,Copy of EarthFault Calcs.xlsx