Who does just a Zs when carrying out a periodic on a lighting circuit

[Hawca]

We don't have to test Ze or PFC as they can be determined by enquiry.
Zs can be calculated using the measured R1 + R2 value added to the enquired Ze value.
That just leaves the RCD test.

this is fine in theory, and thats where it should stay, in design or at college.

Ze by enquiry does not nor will it ever prove beyond any doubt that an installation has a physical earth coming into the installation. the point of the PIR is to see if an installation is safe or fit for use. how can we make a judgement on this if we do not know if an earth comes into the installation?

therefore we have to test Ze, and in order to do so we have to work live.

 

[beaver74]

I have come across a water heater that had a vary healthy Zs which was taken from the water pipe .now if the pipe had been plastic there goes your earth.it is for this reason R1+R2 should be taken to prove an electrical earth