Short circuit contribution

[cppoly]

If a utility transformer feeds a building that contains three separate switchgears, would a motor connected to switchgear #1 contribute fault current to a fault located somewhere downstream on switchgear #2?

For instance if switchgear #1 has a total of 1000A of connected motor current, switchgear #2 has 1000A of total connected motor current, and switchgear #3 has 1000A of total connected motor current, would a fault somewhere downstream of switchgear #2 contain motor contributions from all three of the switchgears (1000A + 1000A + 1000A) x 4?

 

[ron]

Yes.

The three SWGR are connected to the same source / point, so there is a path for short circuit current to migrate from SWGR#1 to #2 if there was a failure on #2.

It is not straight addition, you need to consider impedance

 

[cppoly]

Thanks