r2 testing

[sparks78]

This is mathematically sound provided the T&E is not 2.5/1.0 (which a lot is) but to my mind totally defeates the object of the exercise which is to detect any faults in the circuit. What if the measured value of R2 was 0.46 and R1 was 1.8. Wiould this be detected? Would the fault be detected? Would the fire be prevented?

Shorly it would be better to measure Zs to be certain there was no fault, then if desired calculate R1 and R2.

If only R2 can be measured, eg no time / facility / money to errect scaffolding then let this be an agreed limitation.

Geoff

I have just re-read the original question and note there is an implication that Zs testing is done seperately and in addition to R2 testing. Personally I cannot see the need for R2 testing if there is a satisfactory Zs test. The Zs test confirms the continuity of both the phase and cpc conductors and also the polarity of the supply. The only other test that should be needed is the phase - nutral loop test which is not even called for in BS7671, since this is what controls the current when there is a short circuit and which causes the MCB to switch off. (I am assuming the fault loop is protected by an RCD and it is the RCD that will switch off if an earth fault develops). The only excuse for not doing a phase - nutral loop test is that the Zs test (assuming no faults) would give at least the same and normally a larger value. -- I would be interested in comments on this theory.

Just thought I had to mention this but the r2 test is essential and the ZS test cannot be carried out before you have verified you have a good earth path before energising the circuit. Regarding the original issue its hard to accurately work out the r2 value without further details especially if single cables.

Hi.

As it's a PIR then a limitation can be agreed where you only measure Zs to verify an earth path and not R1+R2 or R2.

I would still measure the continuity of ring final conductors, a blanket IR test (again as a lim) and RCD function.

I wouldn't use the transposed formula of Zs = Ze+(R1+R2) to calculate the R1+R2 as the reading may not be totally accurate due to any parallel paths that may exist.

I agree , I forgot the fact it was a pir, not normally required as long as your clear with the client that you will not be performing the test as its un likely you can garantee no other earth paths.

 

[just add water sparks]

Am i correct in saying the NICEIC require an r1+r2 and a eli test or are they individually acceptable please?????

 

[Guest123]

On the NIC test forms there are columns for R1+R2 or R2, it says at least one column to be completed. So either you do R1+R2 and Zs OR R2 and Zs.

 

[just add water sparks]

thanks

 

[Jason Smith]

Can I just clear something up here, I apologise if I have missed it all through the threads, you only use R1 and R2 for ZS calculations. Not r1 and r2. This may be some of the confusion in the OP.
And thanks to leny I think for answering a question of mine which would of been why the measured ZS never adds up to the calculated ZS, because the measured zs Includes the Paralell paths. We canot disconnect them because the test is alive test and earths must not be disconnected.

Quick tip to the op, dont put a link in the phase to the earth, its dangerous !! even though its shown in all the books. Take the phase wire out and stuff it in the earth bar !! if it wont reach, connector block.