The SOTRs gives a column 18, for the Zs of each circuit. Does anyone have the workout/formula for this?
Discuss Schedule of Test Results (No 18: Zs) Calculation in the Periodic Inspection Reporting & Certification area at ElectriciansForums.net
I always start with calculating ZS as I know this will give me a worst case scenario. My ZS is then measured afterwards to give me the feel good factor (hopefully!)It is arguable that carrying out a Zs test will give you a "real life" reading and so is actually more accurate. This is fine, just so long as any parallel paths giving you an adequate reading don't change (such as a water mains being changed to a plastic incomer).
The advantages of Ze+(R1+R2) are that you are isolating that circuit and so are not dependant on the rest of the installation remaining the same. By linking your line and cpc and testing at each point, you will also be confirming polarity and line switching.
Personally, I use both measured and calculated methods depending on the situation at the time, and I agree with all the reasons why people prefer one method over another.
Totally agree mate. What I should have added is that even when I have calculated my Zs on a new installation, I will always go around before I hand it over and carry out at least one measured Zs on every circuit for the very reasons you have just pointed out. This is why my testing takes so long and I usually end up out of pocket time-wise (not that I care as long as I'm fully satisfied with my results).I have no argument with that mate...on the day you energise the installation, you rely on the actual Zs to meet the disconnect times, but I agree if the calculated fall within the value good to go...BUT what if the circuit under test once reconnected after the R1/R2 test has a fault on it ? lets say the MCB termination has been nipped up on the insulation ? this is why I like to see a good measured Zs..
There are still plenty of us who care mateComing back to this trade after some years messing about with other things, I find myself quietly in awe and humbled that there are so many of you out there discussing things to such depth. I doubt that the average Joe that sees a NIC or NAPIT etc sticker on someones van knows just what that represents! I have spent a long time working in a job where there was a lot of "Oh it'll do wonnit?" going on, and I look forward to coming back to where, well, frankly there will be a bit more "How do we know it will do?" !!!...
GN3 covers more than enough for Testing, and certainly covers in depth Ze and other basic tests.Thanks for the reply. I see where you are coming from. I am actually looking at the question/answer in line with what officialdom would require, i.e. those who set the question & decide what the right answer is. That is why I put this into this forum, as even GN3 cannot & does not cover everything/every eventuality.