ZS

[ezzzekiel]

taking Zs without doing an R1 R2 would mean carrying out a live test without proving cpc exixts.

Dont shoot me mr.Nic made the statement, you can calculate ZS but not R1 R2

 

[needasparks]

We sort of touched on this on the other thread. It would really depend on the agreement from the person ordering the test with regards to isolation for testing, the less of the test carried out then the less value the results are worth which is why it must be agreed first. I think the best way to explain would be to give an example of a poor result but still obtaining a good reading.

A 4mm radial circuit on a 32A MCB with many outlets that cannot be turned off as has a computer fed from one of the sockets there is also a fused spur controlling a boiler wired in 0.5mm flex fed from this circuit. At the the CU the cpc for this circuit has become disconected but a reading of Zs on this circuit is recorded as 0.35ohms which is well within a max for MCB.
Now this circuit could turn out to potentially dangerous if a fault to earth occured on it only having a 0.5mm conection to earth with the pipework on the boiler which is why the Zs only reading is worthless.

 

[Deleted member 9648]

taking Zs without doing an R1 R2 would mean carrying out a live test without proving cpc exixts.

Dont shoot me mr.Nic made the statement, you can calculate ZS but not R1 R2

True on a new install...but the OP is referring to a PIR,which is already energised.

 

[SimpleSimon]

This thread links in to exactly what im doing at the moment, EICR on commercial shops in an Airport. Over 30 boards, not one can be isolated. Some have Ze and PFC recorded from previous Reports so this.can.be recorded but next.to that all i can do is Zs and the occasional RCD test. I can whip the board open to check all connections but nothing more! Very very limited EICR but its all stated and agreed with the person ordering the report. Limited to what can be told about the system.
Sent from my GT-I9100 using Tapatalk

 

[malcolmsanford]

I find this to be quite interesting. We have comments regarding why this and why that. Posts about what can happen or what could happen if that occurred or this was to be, when the bottom line is, an EICR is a report on the installation, not a fault finding exercise.

R1 + R2 proves continuity of the CPC and polarity. totally agree with that and would of course always do it on a EIC/MEIWC, but we are talking about EICR, where continuity of your CPC can be proved by R2, which is why aids like extension poles were invented to help us when it is not feasible to take an R1+R2 reading

R1 + R2 will confirm as part of a formula your Zs reading and is vitally important for disconnection times. Great for initial verification to confirm your design, but I would hope by the EICR stage this design criteria is passed.

I will say the only down to not doing the R1+R2 test is that often you can pick up loose connection with it, and by not doing it they could be missed, but in fairness on a EICR you often do IR tests at 250volt and also just L/N-E, sometimes compromise is needed, this is where your training and experience guides you.

We know the NICEIC stance on "live" working and "testing", that it is not right. Well sorry but like a lot of things in this world I don't hold with that. I want to know what the value of Zs is, when the installation is "live", when it is actually working and when people are going to be using it, not what it should be on a calculation.

In the real world there are parallel paths, and these indeed affect the results on a Zs. But great long may they do, I know that when there is a fault , the fault won't say, hold on that is not fair, I'm going to disconnect quicker because of these paths, disconnect yourself please and let me have a chance to do damage!!!!!

You are reporting on the installations condition, it's suitability for continued use. Great in the classroom and the guides to say these are the tests and this is it. But also remember the same GN 3 tells us, as the inspector WE decide what tests are to be done on an EICR. If I measured 0.25 ohms on a 32amp MCB, and proved there was a CPC by the R2 method at each point, then I would not be knocking myself apart saying but what is the R1+R2

 

[johnboy6083]

bear in miond also that BS7671 does allow us to use extraneous metalwork as CPC, read section 543, and in particular, 543.2.1, and 543.2.6.
This a regulation that is very very rarely used, and i think if it were to be, a lot of testers would fail it, even though it is a satisfactory method of providing a CPC.