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sambotc

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If doing end to end continuity testing on a radial circuit (2391 test board) is there a requirement to carry out R1+R2 as well, and if so what does it prove?

I carried out end to end on the board today as some of the circuit used armour as CPC etc and I was told I should have tested R1+ R2 as well, just wondering if this is a requirement?

I was under the illusion R1 + R2 was used more for convenience, what am I missing?
 
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SirKit Breaker

R1 + R2 is a convenient way of testing the CPC of a long circuit, and by doing this you also confirm polarity, because R1 being you line conductor, R2 being your CPC, when joined together if you operate switches you will see the reading going open circuit, then closed circuit assuming your switches are in the line conductor as they should be. This should have been explained to you on your theory course.

Cheers...........Howard
 
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sambotc

So if end to end is carried out on all conductors, there is no reason to carry out R1+R2? I realise this will very often not be the case, but on the test rig the leads reached so I didn't do R1+R2 as it seemed pointless.
 
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SirKit Breaker

Sam,

I take it you have GN3, this explains it well, but i will try and simplify.

First test on a ring final circuit.
Continuity of ring conductors.
r1,rn,r2, end to end values, and make a note of them.
Cross connect opposing ends of r1 and r2, to make a figure of eight arrangement, then take a continuity reading at each socket outlet from the front of the socket using a plug in breakout box, not at the terminals.
At each socket outlet you will get a reading, this reading should on a ring with no interconnections be the same at every point, and should be a quarter of the value of r1 end to end value, and r2 end to end value when added together. If all your sockets have the same reading, then you have a proper ring, when you test at a spur the value will increase, and it will increase further if there is a spur on a spur. This method also confirms polarity if everything is wired up properly. You then repeat the process but joining r1 to rn and do the same again. These two tests will also highlight any loose/bad connections.
This is the test procedure as per GN3. The long lead method only confirms your CPC continuity.
Hope this helps.

Cheers.............Howard
 

spark 68

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If I remember on the 2391 practical you had to follow the procedures as laid down in GN3.
I know the cables on the test rig were short enough to measure end to end, which they wouldn't be in real life except for the very smallest of circuits, so you had to show you understood the procedure and how you should test in real life.

As Howard said this would show that the CPC was intact, that the polarity was correct, and also give you your R1+R2 value.
 
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sambotc

Thanks, yeah I understand the principles of it, and I have showed that I understand R1+R2 on another circuit on the test board, but the way it was explained to me today was that it had to be done which I found hard to understand for the above reasons.

GN3 states both methods as being acceptable and the EIC's I use state either or on them, but the test schedule's we were using today were the one's from BS7671 and are more simplified.

I just wanted to double check I wasn't missing something but you've confirmed I haven't!

Thanks
 

tigerpaul

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Usually on the test sheets you need to fill in a resistance value for r1 + r2, OR you can fill in a value for just r2.

r2 is for when you use the wandering lead method.

In practice though is it usually better to measure r1+r2 for the reasons mentioned earlier, and also to avoid having wandering leads laying all over the place.
 

spark 68

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Usually the wandering lead or R2 only method is the preferred way on EICR's and the like where the installation has already been in service (powered up), When I did my 2391 we were filling in an EIC as if it was a new installation.

The reason for this is that they are testing you on all aspects and procedures to see that you understand fully both the sequence and the reasons for the tests.
 

dagrat

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On an EICR we are encouraged not to disconnect equipment wherever we can avoid it,and so the r2 method is the preferred method, however the r1r2 method is far more satisfactory on a new install.
The college will almost certainly require you to exhibit understanding of both methods.
 

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