skm modeling of 250' bus duct

[julesm]

Greetings!
I am performing a short circuit and arc flash for a multi-story building with 4000A 480V busduct risers. Each floor has several plug-in breakers. Do I model this busduct as one long bus or each "floor" is it's own bus? I just need to err on the conservative side for a preliminary analysis at this point. Any ideas?
Thanks,

 

[DanDel]

The points where the busplugs are connected should be modeled as buses in the software; the busduct itself should be modeled as impedances between the buses.

Don't be confused by the word 'bus' as it is used in the software; it means a connection point. The busduct is an impedance just like a cable. As a matter of fact, SKM lists busducts in its cable library.

 

[julesm]

Perfect clear answer. It seems so obvious now! Thank you very much.

 

[majesus]

The T&D book is an excellent resource for BUS impedance values. Pg 396 according to my log book

It would be interesting to compare what is the impedance obtained from SKM vs T&D.

 

[alehman]

Bus duct manufacturers publish tables of impedance values as well.