How to calculate Zs

[Shamrez]

My question is:
how to calculate the impedance of all circuits in system
Zs =Ze+(R1+R2) . Do we need to calculate all rings and radial circuits one by one or only one further most (R1+R2).
I red in testing we look at worse Sanario.
All circuits are parallel and adding parallel resistance means sum will be less and at end Zs will be less
I hope you understand my point

Many thanks

 

[SPECIAL LOCATION]

Welcome to the forum..

I think you may be confusing 'Insulation Resistance Testing' with 'Earth Loop Impedance testing'..??

i.e. A global IR test at the CU will include ALL circuits and numerous possible parallel circuit paths, thus will be lower than testing individual circuits..

Whereas reg 314.4 requires that where more than one circuit exists, they must be independent of all other circuits.. Thus circuit 'Earth Loop Impedance testing' will NOT involve parallel paths.

e.g. you can do a global IR at the CU..
But Zs are on individual circuits not at the CU!