Ring r1r2 test

I understand on the initial test/verification of a ring main.

During periodic inspections I connect both lives and earth's of the ring main at the cu and then go around each socket to find the highest reading which I use as my r1r2.

Is this wrong? 

That depends on how you connect them. 

Testing is the same on both periodic and initial verification 

I always believe the aim of the test was to identify the farthest point on a circuit which should also be the point with the highest reading, the point with the worst fault path.

in a ring, you shouldnt have a furthest point, except for spurs. you should have the same reading throughout

I think by "furthest point" he means identifying the spurs

Andy™ said:

in a ring, you shouldnt have a furthest point, except for spurs. you should have the same reading throughout

Click to expand...

only when cross linking L & N

When cross linking L & E, the lesser CSA of the CPC will cause readings to increase the further away from the CU.

So the OP is correct.

Edit; if wired in T&E and if the correct connections are made.

I do mean spurs. Most ring mains I come across have spurs. If you go by the guide for getting an r1r2 result it says to divide the result by 4, which is fine for a perfect ring. If you do it when your result is from a spurred point dividing it by 4 wouldn't be a true reading.

Rob_the_rich said:

only when cross linking L & N

When cross linking L & E, the lesser CSA of the CPC will cause readings to increase the further away from the CU.

So the OP is correct.

Edit; if wired in T&E and if the correct connections are made.

Click to expand...

+1. Something else that might throw people is if it's that old 2.5/1.00 rather than 2.5/1.5 T&E. The cpc resistance end to end won't be 1.67 times compared to the L or the N but even higher.

Murdoch said:

I think by "furthest point" he means identifying the spurs

Click to expand...

I do. People have spurs of rings to sheds feeding lighting, sockets ect

James1978. said:

I do mean spurs. Most ring mains I come across have spurs. If you go by the guide for getting an r1r2 result it says to divide the result by 4, which is fine for a perfect ring. If you do it when your result is from a spurred point dividing it by 4 wouldn't be a true reading.

Click to expand...

The best way to find if you have spurs is to cross connect the L & N conductors, the readings should be the same EXCEPT when the socket is a spur, it will be a bit higher depending on the length of the spur.

The divide by four bit is just a check on your results. You divide the sum of the end to end results of L to L (r1) and E to E (r2) by 4 and you should roughly get the same as the measured R1+R2 you got from cross connecting the L & E.

I do understand the test fine. My point is to get the highest r1r2 reading once any spurs are identified is to link liveried earth's together at cu and measure at the end of the spurred leg.

James1978. said:

I do understand the test fine. My point is to get the highest r1r2 reading once any spurs are identified is to link liveried earth's together at cu and measure at the end of the spurred leg.

Click to expand...

you are not testing only to get a result to put on the schedule, you are also testing for polarity and CPC continuity, so you test all the sockets and record the highest measured value. The socket with the highest R1+R2 might not be at the end of a spur, it might be at the middle of the ring.

James1978. said:

I always believe the aim of the test was to identify the farthest point on a circuit which should also be the point with the highest reading, the point with the worst fault path.

Click to expand...

No, the aim of the test is to confirm that the ring is correctly constructs as a ring, to confirm the polarity and to confirm the continuity of the cpc. The result which is recorded on the sot is the highest impedance point measured on the circuit.

I agree exactly and I'm under the idea that the highest impedance would be a spurred leg from near the middle of a ring main. 

James1978. said:

I agree exactly and I'm under the idea that the highest impedance would be a spurred leg from near the middle of a ring main. 

Click to expand...

Apart from talking of resistance, not impedance, there is the possibility that a spur near the CU would have a lower R1+R2 than a socket at the middle of the ring. it depends on length of ring and distance from CU and length of spurred socket wiring.

So you could find that something is on a spur using cross connected L&N tests, but it might not have the highest R1+R2

Rob_the_rich said:

Apart from talking of resistance, not impedance, 

Click to expand...

And a ring final circuit, not a ring main

Are we all agreed that the highest r1r2 reading where I would expect to get the highest loop impedance is recorded.

I have read with some interest the posts in this thread, it appears that there is some confusion on what the R1+R2 test is, what it can tell you and what readings you should expect.

The R1+R2 test is one of a number of tests used to verify the ring final circuit. The reading you get at the consumer unit for R1+R2 will be the same at each socket on the ring. If all conductors and cpc are of the same diameter say 2.5mm and you get end to end readings of say 0.50 then the R1+R2 readings would be approx half of this at 0.25. This is what you would expect at each socket, I have seen people come to me saying they have found a high reading at a socket and tell me its say 0.30 or a low reading of 0.20, in reality this could be expected and the variation is not enough to cause concern. A high reading of say 0.40 would require further examination, and a number of faults could be the cause. Normally if all the readings are within the parameters of the test results at all the sockets bar one, it could be a faulty socket, where the switching is not working correctly, or as previously discussed a spur.

The highest recorded reading is what goes onto the certificate. There is no furthest point on a final ring circuit, as the circuit could be broken at any point to test the R1+R2. The R1+R2 and end to end tests can also be used to calculate the circuit length,although not required to be included on the certificate it does give you an insight into how the cables are run when doing a periodic inspection.

R1+R2 testing is a dead test and your tester needs to be zero'ed in order to get correct readings, faulty readings could be down to contacts with the probes, low battery on tester or connections amongst others. When testing it is always a good idea of what you expect to see, and not just except what you record.

First off, if you need to ask you should not be testing anyway.....

Secondly, in a properly constructed ring, as Andy says, it makes no difference WHATSOEVER where you measure, the results will be exactly the same. [Unless of course, as you have forgotten the continuity tests [r1 r2 rn] you have not noticed that there is a break in the ring.

john..