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Topic Title: R1 + R2 or R2
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Created On: 25 May 2014 10:40 PM
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 25 May 2014 10:40 PM
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dsndmedic

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I've been doing periodic inspection today - the DU is quite big and tightly wired and I'm finding it hard matching earths and neutrals to the live on the T & E ring ccts. I thought I would just take the R2 reading instead the realised that I'd have to take a Zs measurement as I couldn't calculate it. I am considering crossing over the live and earth (R1 + R2) at the socket and taking the reading at the DU......is there anything wrong with doing it this way around?

Thanks in advance for your replies.

Andy
 25 May 2014 11:11 PM
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CopperRod

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Can be done at socket.
 26 May 2014 12:35 AM
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mapj1

Posts: 4103
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If I have the right picture its fine, short one end, measure the other, same wire either way round...
Please remove the shorting plug before power back on of course!!
You may want a shorting plug with the fuse bypassed to avoid a few spare milli-ohms sneaking in, but on a normal length circuit its with resistances of several hundreds of milli-ohms its lost in the noise and not worth it.

(13A fuse dissipates <1watt at 13A, so resistance =1/169 of an ohm, or 7milliohms or so)

-------------------------
regards Mike
 26 May 2014 10:27 AM
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Zs

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I've done that at times. Sometimes it is impossible to decipher an earth bar.

Do any of you use the R1+R2 function on the Megger 1700 range or know anything about it?

I have just recently done that for the first time. I did it to alleviate boredom really, and see what it was all about. It involves taking Ze as a reference and then setting to R1+R2 for each circuit tested. But, I wonder about it. You still get to choose high or low current so it is probably just maths in the machine. The sums didn't match perfectly. Not far off though.

Zs
 26 May 2014 10:39 AM
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James231283

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I would be very cautious about putting your name to any type of ring final circuit testing other than the advised method as set out in GN3.
I can see various potential problems with undertaking this test in the particular way that you mentioned. The most obvious to me, would be that you will then record your circuit Zs at the D/B after crossing over conductors at a socket outlet, however the Zs of any circuit should always be the point with the highest resistance value........how will you ensure that there are no spurs on the ring, which would result in higher resistance values and subsequently your true value of Zs, if you are not testing at all socket outlets?

Also, without carrying out end-to-end continuity tests of the conductors (because you are unable to identify which CPC's and Neutrals relate to which Line conductors) you will not be able to ensure that the Line and Neutral conductors of the T&E are substantially the same resistance value, with the resistance value of the CPC being approximately 1.67 times higher than that of the Line & Neutral conductors for a 2.5T&E. The purpose of obtaining this information on a ring circuit is to ensure that there are no potentially loose connections or possible interconnections.

Another thing to always bare in mind is that all dead testing should be carried out prior to live testing, therefore if you are unable to achieve results for the dead test due to not being able to identify the corresponding L, N, E conductors at the D/B for a given ring circuit, then live testing should not follow. However I happen to think that obtaining a Zs regardless of any other testing is always advantageous, but there are grounds for you to advise a limitation here, or advise further investigation in order to obtain a correct understating of the circuitry. To back this up, if the conductors of a ring final circuit are not labelled or connected in sequence this is an inspection point in itself.

Hope this helps in some way.
 26 May 2014 10:53 AM
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phantom9

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Andy, why would you want to do an R1+R2 and an R2? You are just checking that the cpc is continuous. Either test will do.

We have had these discussions on the forum so many times about worrying over the value recorded and whether the Zs should be done as well as the R1+R2.

My take is you need to put a pragmatic hat on and make professional judgements based on your understanding of the circuit.

Don't bother with an R1+R2 on the sockets. Take several Zs readings and judge whether they are reasonable. Do an r1, r2 and rn test at any socket to test that the ring is intact. That is perfectly professional and perfectly acceptable.

You can do a mathematical check using r1 and r2 values for an R1+R2 but its pointless. Consider that it is an old installation and you can only check what is reasonable to do so. If the fuse board is messy and difficult to work on, say so on your test sheet and explain why you tested using other methods.

The preoccupation on this forum with "proper" tests is unbelievable. On an EICR you are making a judgement call based on your experience as an electrician and your knowledge of circuits as to whether the installation is safe. You are not taking responsibility for it , you are not expected to do a perfect test regime and you certainly cannot inspect every bit of it. Stop worrying.
 26 May 2014 11:08 AM
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Banners

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Totally agree with phantom9. In all the periodics I do I take Zs readings at all sockets and always put in R1 + R2 as a calculated figure (Ze - Zs). Where I am going to get a ridiculously low value I put in a nominal 0.1ohm value.

Edit: Yes, that would be Zs-Ze.
 26 May 2014 11:14 AM
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perspicacious

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" the DU is quite big and tightly wired and I'm finding it hard matching earths and neutrals to the live on the T & E ring ccts."

You could start with recording observations of breaches of general characteristics 314.1 (ii) & 341.1 (i) and then follow up with implementation of these in Part 5 with a breach of 514.1.2.

Successful ways and means of getting your test results without recording the basic installation breaches leading to your difficulties, perpetuates poor installation work.

Regards

BOD
 26 May 2014 11:18 AM
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perspicacious

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"In all the periodics I do I take Zs readings at all sockets and always put in R1 + R2 as a calculated figure (Ze - Zs). "

That's odd, my copy on p402 is headed test....

Regards

BOD
 26 May 2014 11:40 AM
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GeoffBlackwell

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Appendix 6 is just 'Informative'.

The 'test' indicated by 612.2.1 does not completely specify a test method or the format of the result - so a simple statement that it has passed would do.

I have constructed a nice 'electronic' bell & battery set that meets the requirements of BS 61557-4 .

Regards

Geoff Blackwell
 26 May 2014 04:58 PM
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mapj1

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Also, without carrying out end-to-end continuity tests of the conductors (because you are unable to identify which CPC's and Neutrals relate to which Line conductors) you will not be able to ensure that the Line and Neutral conductors of the T&E are substantially the same resistance value, with the resistance value of the CPC being approximately 1.67 times higher than that of the Line & Neutral conductors for a 2.5T&E.


Are you sure
- I'd expect ring-round test to read the same to within test gear tolerances if you break the ring at any on point, consumer unit or not. It'll be pretty obvious 10 secs in to testing if you have opened the ring in the middle of a doube spur. The risk of the unknown spur down the back of a wardrobe is always there, but one can make assumptions about the layout of the building if high loop impedance is likely to be a problem in practice if you've selected the wrong 'far point'. A socket near the CU should be similar to the CU.

-------------------------
regards Mike
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