Discuss Schedule of Test Results (No 18: Zs) Calculation in the Periodic Inspection Reporting & Certification area at ElectriciansForums.net

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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.

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!)
 
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..
J
 
Coming 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?" !!!...
 
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..
J

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). :)

- - - Updated - - -

Coming 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?" !!!...

There are still plenty of us who care mate :)
 
(a) Deriving Zs by calculation: (with Ze, having been tested for previously, & (R1+R2) having been tested for previously, to give you the theoretical Zs, &

(b) Deriving Zs by practical: Testing the Zs, i.e. without having to carry out the Ze test.

The issue of parallel earth paths leads to one question mark, whilst the other issue is having to carry out a Ze, which entails disconnecting the supply earth, & then insuring that you do reconnect this.

Is there not a case for doing both also, i.e. theoretically & practically, because both have their advantages & disadvantages, therefore would some installations not benefit from both being carried out.
 
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I did an EICR on Friday in an empty house GREAT I did measure the Ze Zs and did the R1+R2 but we are missing a point here the Schemies are the first to berate you if you work out R1+R2 by calculation ie take the Ze reading away from the Zs and fill the box in but because the Schemies are happy to badge companies who do what i call drive by testing surprise surprise it is them who are cutting corners
 
Is there not a case for doing both also, i.e. theoretically & practically, because both have their advantages & disadvantages, therefore would some installations not benefit from both being carried out.


Ashley, you have to do the R1+R2 (As well as giving you a value it gives you a continuity test on the CPC) and you have to do a Ze ( your obliged to test for the provision of an Earth and check it's value), so you will always have the calculated value ! as stated anyone worth their salt wouldn't rely on this and would compare the tested against the calculated to make sure something hadn't gone belly up when you reinstall the board or accessory connections.

J
 
Yep a bit like the PAT testing you get guys who have done it for years yet when you ask a technical question and you get I just push the button and the tester says pass or fail a bit like little Britain the computer says no
 
LOL mate..well sorry they have made it the Suffolk borders..web feet and all..ah Norfolk many a happy day there at Sea Palling beach..Awesome waves

J
 
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.

GN3 covers more than enough for Testing, and certainly covers in depth Ze and other basic tests.

Cheers..............Howard
 
But GN3 cannot cover everything, it is just a progeny of BS 7671. However, I do grant that it is THE MOST IMPORTANT DOCUMENT, relating to Inspection & testing, I myself revere it in that regard.
 
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...was up for revering it till i read Figure 2.4b Page 41........want me 30 squid back........:smilewinkgrin:
 
Yes, would agree with you, circuit-breakers should be in the off position. But I doubt if there is a single book out there that did not make at least one mistake. That does not detract from the high value content of GN3.

I also like the fact that it is around the 100 page mark, which is another refreshing aspect, because they could so easily have doubled this to 200+, by more detail & explanation.
 
...was up for revering it till i read Figure 2.4b Page 41........want me 30 squid back........:smilewinkgrin:


Is there much difference between the red and green version as I have'nt bought one . I was'nt going to either but a few time my finger has been hovering over the one click buying on Amazon lol. Is it worth buying for the changes? Ta.
 
Is there much difference between the red and green version as I have'nt bought one . I was'nt going to either but a few time my finger has been hovering over the one click buying on Amazon lol. Is it worth buying for the changes? Ta.

Naa just leave it for another year then you can buy the updated one thats after you have bought the new orange OSG whilst you save up for the replacement ISI&TEE (formally) PAT
 
Naa just leave it for another year then you can buy the updated one thats after you have bought the new orange OSG whilst you save up for the replacement ISI&TEE (formally) PAT

I vowed to myself I would buy no more "updates" but my curiosity gets the better of me. Amazon makes a fortune out of me with electrical books lol, sucker for them, same as gear .To old now to change:present:
 

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