Zs taken by live test and r1 r2 calculated by deducting Ze or Zdb

CAN ANYONE OFFER A DEFINITIVE ANSWER TO THIS QUESTION. PLEASE READ AND ANSWER ACCORDINGLY......................

This thread has gone a way I never thought possible, I'm now getting pulled up for grammar......... LOL..... Can I refer back to the original question...... and take Initial Verification out..... If we can do live testing ZE/ZDB and ZS, why is it frowned upon to back calculate to put in R1 R2 (hope I got it correct this time)? This is all I'm asking nothing more? As I have already stated that the FICA asks them to use a crocodile clip from the circuit they are testing on the earth bar so you are using the earth for the whole installation. I AM ASKING WHAT IS THE DIFFERENCE FROM DOING IT THAT WAY OR LIVE TESTING AND BACK CALCULATING. NOTHING MORE I AM ASKING WHY???????????????????

Ro, have we not answered your question? If something is unclear, please say so in order that we may try again.

AS ABOVE

I do feel that the whole thread has ended up as being 'at cross purposes'.

On the one side we have technical explanations about the quality of the different approaches.

On the other side we have (or want) administrative explanations needed for the apprentice training.

We had two approaches (to taking a measurement) that appear to give 'different' results, with a 'correction' allowed one way, but not, apparently, the other way. 

It's the "administrative" 'excuse' for the 'not the other way' that's required.

If I read the threads correctly, it is because we shouldn't make things look 'better' than measured, plus other factors based on the different ways the tests are set-up (short at the board vs at the far end, etc).

And we are looking for a solid apprentice "yes/no" level clarity. No wishy washy qualitative senior engineer stuff .  Is that a fair assessment?

Well done Philip, that is exactly what I'm looking for, an idiot proof answer to the original question which, going by this thread is very hard to get.

OK then, if you want to calculate R1+R2 from Zs-Ze, fill your boots! But what is the point? Are you just being a slave to an empty column on a test sheet? 

If we are only talking ADS, then once you have Zs, R1+R2 is totally superfluous. 

Read the question at the top. I do not want to do anything. I'm asking a question that seems impossible to answer going by this thread. Unless of course I am missing something.

the question has, I think been answered about ten posts up, and the answer is 'no' - its not the only reason. 

That is because there is a safety reason for doing this, though the risk balance is different for existing circuits vs brand new ones, and inspections of unknown or only partly accessible installations may require more inventive approach.

Also it would be better if your apprentices actually verified the continuity of circuit CPC rather than a CPC that may be partly shorted along its length, as that paralell route may be hiding a break or high Z joint in the CPC.
For insulation tests however, all fault paths, not just to CPC should be explored, and that favours the MET and CPC to be connected.

regards Mike.

Is the only reason you do not calculate r1 r2 by deducting Ze/Zdb from Zs is that it is down to parallel paths. The reason I am asking is, when the apprentices are doing their trade test, they are encouraged to short the circuit they are working on to the earth bar via a crocodile clip to get r1 r2. Surely this is picking up parallel paths also? Or is there is another reason?

THIS IS THE ORIGINAL QUESTION, PLEASE SHOW ME WHERE IT HAS BEEN ANSWERED?????

AGAIN I'M NOT ASKING HOW TO TEST OR WHAT SHOULD BE DONE TO DO IT SAFELY.

Ro said:

Read the question at the top. I do not want to do anything. I'm asking a question that seems impossible to answer going by this thread.

Ro said:

Is the only reason you do not calculate r1 r2 by deducting Ze/Zdb from Zs is that it is down to parallel paths.

No. At initial verification, you measure either R₁ + R₂ or R₂ on its own before the installation is energised.

Strictly speaking, as GK has written below, Z_S = Z_DB + (Z₁ + Z₂), but I would not quibble about impedance as opposed to resistance, particularly at the domestic level.

Ro said:

Or is there is another reason?

Aside from safety and parallel paths, the errors in the measurement of EFLI are greater than the measurement of resistance.

A further reason is that it is not required for periodic I&T. Continuity of the CPC may be confirmed by Z_S at accessible sockets, etc.

Ro said:

Read the question at the top. I do not want to do anything. I'm asking a question that seems impossible to answer going by this thread.

Ro said:

Is the only reason you do not calculate r1 r2 by deducting Ze/Zdb from Zs is that it is down to parallel paths.

No. At initial verification, you measure either R₁ + R₂ or R₂ on its own before the installation is energised.

Strictly speaking, as GK has written below, Z_S = Z_DB + (Z₁ + Z₂), but I would not quibble about impedance as opposed to resistance, particularly at the domestic level.

Ro said:

Or is there is another reason?

Aside from safety and parallel paths, the errors in the measurement of EFLI are greater than the measurement of resistance.

A further reason is that it is not required for periodic I&T. Continuity of the CPC may be confirmed by Z_S at accessible sockets, etc.

Chris Pearson said:

No. At initial verification, you measure either R₁ + R₂ or R₂ on its own before the installation is energised.

I might add that 643.7.3.1 states, "An electrical continuity test shall be carried out according to Regulation 643.2 before carrying out the earth fault loop impedance measurement."

So before you even know Z_e and Z_s, you already know R₁ + R₂ or R₂.