Measure or calculate your Zs?

[spud1]

Hi again!

Which value is best to record in a certificate or report, a max measured or a calculated Zs?

I know Sparkies who do it both ways, but personally I take measured values at all the points of utilization to find the highest, then I calculate Ze+(my highest R1+R2) for the circuit and then I compare the max measured and my calculated values and record the highest of the two on the certificate.

Any thoughts?

 

[Deleted member 26818]

Don’t know what the current version of GN3 advises, but my old copy says that a Zs test at socket-outlets and at exposed conductive-parts of equipment on other circuits, is sufficient to confirm continuity of the CPCs. That’s for periodic inspections.

 

[Bestsitespark]

Both work in conjunction with each other, all sparks should use both, the calculation proves what the Zs should be without any parallel paths if there is any, it also shows if the maximum permissible Zs could be exceeded, but this doesn’t give proof of the earth loop so the test is required.
The test proves you have an earth loop, if it’s lower than expected it’s likely there are other earth paths and if it’s higher than expected then this indicates a problem.
Only doing the calculation is to me just a bit lazy and potentially very dangerous