Getting A Zs reading from lights

[Mfctitch]

Hello Everyone
I have looked at a few of the past threads but can not an answer for this question.

I am still getting to grips with my testing before applying to the NICEIC. Was helping a friend out and thought I would test his lights. As he has loads of spots I done an R2 test with a wander lead. The problem is that when I went to do A Zs test first I always have a problem getting my machine to register when measuring from the switch and when I try to measure from the light itself the MCB trips out.
So how apart from putting a larger MCB in its place, Which I know a lot of people do not recommend how do I get the measure by calculation?

The machine that I am using is a Robin KMP 4120DL PSC-LOOP Tester

Thanks for any and all replies

 

[telectrix]

measure your R1+R2, then calculate Zs from Zs=Ze+(R1+R2). or use no-trip Zs test.

 

[Sparky Ninja]

For the purpose of your inspection it would be better to stick to the calculation to remain in accordance with regulation 14.

In the real world, the advise telectix has given with regard to the no-trip setting will be best.

 

[Mfctitch]

wow quick reply only had time for a shower.
I understand about doing R1+R2 but was wondering if there is a way to calculate after only doing an R2 test?
Also my machine does not have a no trip setting :-(