Defo not a waste of time! Ok so you did your R1+R2 test , which you disconnected at the CU, measuring your Zs is the only way to prove you remade the connections properly and also to establish wether or not there is a possible loose connection in the circuit.
Do it Properly
What did I disconnect and reconnect?
To carry out my R1+R2 test I merely add a link between the top of the circuits MCB and the earth bar within the consumer unit. I then go to all areas measuring R1+R2 and record the highest figures. When I've done this with all circuits I remove the link from the earth bar.
That is doing it properly and safely. I think you need an understanding of how to test if you don't agree.
Also, if you can't disconnect a conductor and reconnect with visual verification then you've no right to be in this industry.
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Regulations state calculated is an accepted method, and R1R2 tests should be carried out so if you wish to use a calculation or go on and do a live zs either is acceptable - cant see the problem
No problem but live Zs testing is replicating a previous test but with added dangers of live testing which should be avoided if possible.
Imaging stood on a pair of step ladders with your meter set to no-trip mode due to the circuit being on a RCD. Many testers then require all 3 probes to carry out a Zs test which can be awkward, especially at height. It's just not required.