Ze and zdb

[Rockomuir]

Evening, if say for example I had a ze figure of 1.0 at origin, and I had a Zdb from a sub main to dist board figure of 1.1. To calculate zs is the calculation zs= ze+Zdb+ r1+r2 for the individual circuits.

Many thanks

 

[brucelee]

Yes mate
for a DB supplying a sub board its
Zs=Ze + (R1 + R2sub main) + (R1+ R2final circuit)
the SUB MAIN R1 + R2 IS THE ZDB ALSO fir that board
So measure your Zdb and add to the R1+R2 of final circuit and thats your ZS for the final circuit

 

[Rockomuir]

Thank you for the reply, that helps make clear why my zs results are a little out

 

[sparks_114]

Sounds good to me: Zs is the whole impedance, Zdb is the impedance up to the DB where a distribution circuit is involved, Ze is the impedance external to the installation and hence measured at the point closest to the service head. Only thing to watch out for is that you don't count the impedances twice; ie Ze+Zdb. Zdb to my knowledge is the external impedance + the resistance of the distribution circuit conductors (R1+R2). So unless you're going to measure R1+R2 on the distribution circuit (which'd require safely isolating the distribution circuit cable) then add to Ze to get Zdb I'd measure Zdb live then add R1+R2 on the final circuit to get your Zs.Hope this helps.

 

[Sparky Ninja]

To calculate zs is the calculation zs= ze+Zdb+ r1+r2 for the individual circuits.

Remember that Zdb incorporates Ze, and so Ze+Zdb should not be in the same formula.

 

[T&Earth]

Hi Guys
Sorry this may be a silly question, but I recently installed a main C/U on a TT system and a sub C/U board in an out building. Both of these systems or on seperate rods and are only connected to there indiviual earth rod, so when i'm trying to calculate the Zs on a final circuit is the sum: R1 + R2 of the supply cable to sub board + Ra of sub board + R1 + R2 of sub board final circiut??
Sorry for this long winded post, your help with would be appreciated

Many Thanks
T&E