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Topic Title: R2
Topic Summary: R2 test
Created On: 07 July 2014 03:15 PM
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 08 July 2014 12:38 PM
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GeoffBlackwell

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John
That tester is only one stage away from my use once devices - have a care .

Regards

Geoff Blackwell
 08 July 2014 01:15 PM
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Parsley

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Many years ago I worked for AGA and was given a nice Clare tester in a wooden box and the these instructions http://www.rayburn-web.co.uk/P...2%20EINS%20511088.pdf

I like the please note on page 1.

Regards
 08 July 2014 03:51 PM
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gchar

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Hi
Got all the correct responses from you guys both R2 and R1 + R2 have their places when carrying out the various tests I think its is more practrical to carry a R2 test on an exsiting installation and R1 + R2 on a new installation. In this case all your reading an other tests have all ready been done.
 08 July 2014 09:36 PM
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leckie

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We'll I know Geoff won't reply because he has already said he wouldn't

But I am a bit confused by this. We are being discouraged from taking live Zs tests in favour of doing R1+R2 tests and adding them to Ze? Oh and I know there is a difference between impedance and resistance.

I personally continue the "unsafe" practice of carrying out Zs tests when I can, the same as I have for the last 40 years.

But the R1+R2 + Ze method is described in Guidance notes, various text books, etc. So it can't be complete tosh. And even if the absolute accuracy of the result obtained is dubious, it is what is described as an approved method. A working electrician is not a technical genius that can work all the aspects of testing, etc, for him or herself. Guidance is required. So if we cannot use the methods detailed in the IET Guidance Notes, approved by the various trade bodies, etc, what are we actually expected to do?
 08 July 2014 09:40 PM
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phantom9

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Strip away all the baggage and you have a need to verify continuity of the cpc. All this clever talk and what if this and the other is astoundingly wide of the mark. It was explained to me quite easily and simply by a very good college lecturer when I did my C&G236 part1. If you just did a straight install and didn't do any tests you would never know whether there was a break in the cpc, It doesn't carry current except under fault conditions and it may never do so. It needs to be tested for continuity. It is a dead test, designed to verify the cpc before the new circuit is energised. On older circuits that have been butchered over the years by unscrupulous meddlers who knows what may lay hidden. Doing an R2 or an R1+R2 is only a check in these situations because no matter how clever you think you are you cannot be 100% certain of anything on a circuit installed by someone else it is impossible. You can only form a judgement about it based on what you do. If there are crossed cpcs or parallel earths so fn what! It really doesn't matter if there is a continuous earth path it will disconnect a fault. How will you know whether there is a break in a cpc on a parallel earth path? You won't. How can you? It will be continuous. Writing down a number is meaningless, its just to record the fact you've done the test.

All this smart retort, Oh I thought Zs=Ze +(R1+R2) just shows how dumb some people can be and how they focus on test results and numbers instead of the basic reason for the test. It makes so mad to argue with people who should know better, they just seem to enjoy showing who knows the most. It is harder for some to understand very very basic concepts it would seem and then go off on tangents giving complicated and unnecessary scenarios. Inventing all sorts of weird and wonderful reasons for doing certain tests and what the values mean. Did you know that the values are "designed" to fit circuits. They are not magic numbers. If a circuit is within usual tolerances in terms of cable size and length to suit the design load the R1+R2 or R2 values will ALWAYS be okay. People who fuss over minute details like what value the reading should be and what if Ze is this that and the other are putting the cart before the horse. It is so simple yet everyone makes it so much more complicated than it actually is. I blame the design of the forms for a lot of the nonsense. Requiring values to be recorded takes the focus away from the meaning and purpose of the test. Its clear from reading the smart alec responses to be honest. Geoff Blackwell seems to understand my point. glad someone does!!!!

Edited: 08 July 2014 at 09:49 PM by phantom9
 08 July 2014 09:52 PM
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gchar

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Guys we all understand what R2 and R1 +R2 are all I need to know is it wise to record both reading on a test form
 08 July 2014 09:56 PM
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phantom9

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Originally posted by: AJJewsbury

The purpose of the R2 test, or the R1+R2 test, is very simple. It is to prove the continuity of the cpc.


What if the c.p.c. is been crossed with L? What will the R1+R2 test show? Does it really prove c.p.c. continuity on its own? How do you show that Zs will be adequate when you're in a situation where the permanent supply isn't available during testing? (e.g. mobile unit or new development where the supplier requires a 'dead tests' certificate before connection). As leckie pointed out, Ze + R1 +R2 is an acceptable approach.



BS7671 - 612.2.1 simply requires a continuity test.


For continuity yes, but the regs also requires us to verify Zs (612.9), and in practice the result of R1+R2 is often used as part of that process (two birds with one stone kind of thinking). For instance one well known organisation recommended doing R1+R2 at every point, but a live loop test only at the point on each circuit with the highest R1+R2 (to minimise live working) - without knowing the value of R1+R2 that process breaks down. Some even suggest always using Ze+R1+R2 and eliminate live working Zs altogether.



Then with the ring circuit's version of the R1+R2 test ((r1+r2)/4), you should consider the measured values as it's unlikely that there'll be any convenient terminals at the exact mid-point of the ring to do a Zs loop test at - the worst-case point of the circuit. (Notwithstanding Geoff's comments about the precision of instruments and so whether at a near-by socket would be 'good enough', in most circumstances at least.)



- Andy.


Andy if you really feel that you know more than the IET do about the components of a test why don't you ask them to expalin why! It has sod all to do with Zs=Ze+(R1+R2). Its called mathematics and that's just what that equation is. The different components of the equation have their own defined methods of being measured. That equation is just how they fit together. You don't do one test to establish what the other tests are. It is useful comparison and can be used to put values in to boxes. (R1+R2) is a convenient way of establishing continuity of the cpc using one of the other two conductors. Rn+R2 would give you exactly the same result and would be just as acceptable. R2 is measured with the wandering lead, it is directly establishing continuity. Ze is the external earth fault loop impedance and is a live test, it cannot be carried out dead because the neighbourhood would complain bitterly about having their power cut off so you could measure it with your continuity tester! The Zs test is a live test, by definition the complete earth fault loop impedance including the external component and the circuit inside and it is a live test. P=IV, its just another equation. V=IR, its just another equation. Testing is the art of measuring the components that together make the earth fault loop, a continuous fault path from the origin to the star point back along the PEN in to the ciruit in the house and back round to the origin. If that loop is complete by measurement then we can look at the values and decide if they are acceptable.

Edited: 08 July 2014 at 10:09 PM by phantom9
 08 July 2014 10:27 PM
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leckie

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Calm down Phantom you'll blow a fuse in less than 0.4s!

OK, so I was digressing from the OP's point and moving into measurement of Zs territory. But bear with me a little bit.

So out of interest, how would you assess Zs? Do you mean you would not use the Ze + R1+ R2 method? Do you think only direct measurement is worthwhile? Or neither? Geoff seemed to suggest that both ideas were pointless, and I know he is a super clever chap so I know he will have a reasoned argument for his point of view.

I know that it matters not if a cpc is continuous or not from the point of view disconnection under fault conditions. I also know that parallel paths can alter test results, etc. but GN3 etc, give guidance on tests, sequence of tests, etc, so what do you think are the requirements?

Should we just tick R2 and R1+R2 boxes after ringing out with a bell set?
 08 July 2014 10:34 PM
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AJJewsbury

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Andy if you really feel that you know more than the IET do about the components of a test why don't you ask them to expalin why! It has sod all to do with Zs=Ze+(R1+R2)

I think you'll find that the IET and I are generally in agreement. If you've a copy of the latest GN 3 look at the last but one paragraph on page 32.

If you think that the R1+R2 test alone proves c.p.c. continuity, draw out a diagram of a socket on a radial circuit with c.p.c. and L crossed and see what result the R1+R2 test would give. (BTW that's the fault that killed Danny Edwards - http://www.hse.gov.uk/press/20...birakosenterprises.htm )

Rn+R2 would give you exactly the same result

Not necessarily - lighting circuits for example typically have higher R1 than Rn due to switch drops. There was a time when N-PE loop resistance was measured in an attempt to check the value of loop resistance, but that approach fell by the wayside may decades ago.

- Andy.
 08 July 2014 11:36 PM
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AJJewsbury

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They say a diagram is worth a thousand words, here's one that should look a bit familiar:

but look carefully.

Does the meter give a sensible value for R1+R2 consistent with cable c.s.a. and length?

But is the socket PE contact correctly connected to the c.p.c?

- Andy.
 08 July 2014 11:41 PM
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sparkingchip

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ell, my dear P9, consider my example of the heater and metal bodied thermostat where power calls in at the heater, and there is as bit of T/E between heater and the thermostat.
Where would you measure R1 +R2 or just R2 to get the worst case fault current - heater or thermostat and ensure the CPC reaches both places ?
I'd do two tests, one of each flavour , but I suppose you could do two of the same - but I can't see any way where one single figure covers all the bases correctly.
Sensible & technically ordered answer only please, and bonus points for how much you would actually record, and how. "

On Minor Works certificate the result of the earth loop impedance test, which confirms CPC continuity if done in an appropriate manner. If carried out as a "high current" test it probably produces a more meaningful result as well.

I would suggest that following your testing regime you would eventually confirm continuity three times, perhaps a little over zealous?

Andy
 08 July 2014 11:59 PM
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mapj1

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Deep breath, hang on in here.
If you measure R2 , or R1 + R2 at the heater, and I don't care which, truly, you may confirm the live path through the thermostat in one case, and you certainly confirm the CPC route is good from the CU to the heater. ONLY.
Now it you think AHA when we consider the route taken by the CPC then the thermostat is the furthest point, then you should do the R1 +R2 test there instead.
So, I claim, if you do an R1+ R2 at the heater, then to give full test coverage, you also need an R2 at the thermostat as well.
Or you could just power it up and see if it works to test the R1 part...


The merits of testing with 100A off a car battery or something to shake out any 'hanging by a thread' stuff can be debated, but lets do that as a separate topic.

Polarity is something else, and just plugging in a test lamp and seeing it not go on would have been enough for that.

-------------------------
regards Mike
 09 July 2014 05:53 AM
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GeoffBlackwell

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See my Avatar

Regards

Geoff Blackwell
 09 July 2014 08:17 AM
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phantom9

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What are you talking about "sensible value" for R1+R2. None of you get it do you. Copper has a fixed resistance per metre. You are all making a big deal over the numbers and not what you are testing. Sensible value for R1+R2, omg. Draw lots more diagrams if you want, it doesn't change the REASON for the test.
 09 July 2014 08:54 AM
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sparkingchip

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The continuity test is to confirm the CPC continuity, R1 is taken in lieu of using a wander lead. R1+R2 is useful to know, but it is still the R2 element we are confirming with the dead testing.

If you need to confirm continuity on the live conductors just remember there are two of them on a single phase circuit, live and neutral. Loop testing on "low current" generally indicates when there are issues with the neutral as well as the live and CPC, so perhaps a more efficient test.

Andy
 09 July 2014 09:33 AM
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AJJewsbury

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What are you talking about "sensible value" for R1+R2. None of you get it do you. Copper has a fixed resistance per metre. You are all making a big deal over the numbers and not what you are testing. Sensible value for R1+R2, omg. Draw lots more diagrams if you want, it doesn't change the REASON for the test.

Look at it again phantom9 - I think you've missed the point. I'm suggesting that in this case the meter will give a sensible value, but the c.p.c isn't correctly connected. Hence the logic of using the R1+R2 test alone to prove c.p.c. continuity is flawed.

- Andy.
 09 July 2014 10:44 AM
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sparkingchip

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CRISPER

Continuity of circuit protective conductors

Resistance of circuit protective conductors

Insulation

Separation of circuits

Polarity

Earth loop impedance

RCD test times

That covers circuit testing with polarity being confirmed separately to R2 by ticking a box on the test result sheet.

You can combine testing to get more than one test complete at the same time.

But in reply to the original post, no you don't need to record both R1+R2 and R2.

Andy
 09 July 2014 11:13 AM
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GeoffBlackwell

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Originally posted by: sparkingchip
Resistance of circuit protective conductors
Andy


Really - is this a new requirement, what is the regulation number that requires it?

Regards

Geoff Blackwell
 09 July 2014 12:20 PM
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sparkingchip

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Resistance of circuit conductors, sorry Geoff I'm getting over excited by the topic! The original poster only wanted to confirm what to record on the test results schedule and we're giving him the full chapter and verse.

I was just trying to point out we confirm polarity later in the test sequence.

Andy
 09 July 2014 01:41 PM
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sparkingchip

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612. 2.1

Continuity of protective conductors including main and supplementary bonding.

A continuity test shall be made.

612. 2.2

Continuity of ring final circuit conductors.

A test shall be made to verify the continuity of each conductor , including the protective conductor, of every ring final circuit.

No requirement to check continuity on radial live and neutral conductors or any mention of obtaining resistance readings at all in the regs.

OSG 10.2- Note: The advice give does not preclude other test methods.

So are you happy with me ringing a bell to check continuity, then ticking a box on the paperwork rather than entering a precise resistance reading?

Andy
IET » Wiring and the regulations » R2

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