Funny end to end and R1 + R2 readings

[ajl_02]

I recently changed the fuse board in my house as I job I am goin to used for my nic assesment. Upon testing this I have come across a ring circuit which does part of the kitchen and part of the utility room. When I measure the end to end from the fuse board I get r1=0.12 rn=0.12 and r2= 0.18. The values seem a bit low for the circuit but are still ok I thought. Then I crossed the r1 and r2 cables at the board and went and tested every socket and I get a R1 + R2 reading of 0.43. I tried every socket on the circuit and they are all high and very similar results.
To confuse matters even more I put all the cables back in the at board and decided to get an end to end reading on the same circuit from a socket on the same circuit and I get the values r1=0.43 rn=0.43, r2 = 0.63 and R1 + R2 = 0.48.
Taking the values measured at the socket seem more realistic considering the length of the run but can't understand why I'm getting completely different results when the tests are performed at different points on the circuit. I thought maybe it could be a ring circuit within a ring but would just like to get more of an idea before I start stripping the circuit down. Any help would be appreciated. Adam

 

[malcolmsanford]

I recently changed the fuse board in my house as I job I am goin to used for my nic assesment. Upon testing this I have come across a ring circuit which does part of the kitchen and part of the utility room. When I measure the end to end from the fuse board I get r1=0.12 rn=0.12 and r2= 0.18. The values seem a bit low for the circuit but are still ok I thought. Then I crossed the r1 and r2 cables at the board and went and tested every socket and I get a R1 + R2 reading of 0.43. I tried every socket on the circuit and they are all high and very similar results.
To confuse matters even more I put all the cables back in the at board and decided to get an end to end reading on the same circuit from a socket on the same circuit and I get the values r1=0.43 rn=0.43, r2 = 0.63 and R1 + R2 = 0.48.
Taking the values measured at the socket seem more realistic considering the length of the run but can't understand why I'm getting completely different results when the tests are performed at different points on the circuit. I thought maybe it could be a ring circuit within a ring but would just like to get more of an idea before I start stripping the circuit down. Any help would be appreciated. Adam

I would imagine has you have put the cable back into CU your picking up parallel paths through your common Neutrals and CPCs, which is one of the reasons we do not test RFC in this way.

The 0.43 reading to be honest is not a surprise either. As it is an existing installation you may find that the sockets are old and your lead is not making a good connection. Try plugging the lead in and out a few times and see if it makes a difference. Also they maybe cheap sockets, there can build build up on the terminals, there maybe a JB lurking somewhere, there are numerous reasons on an older installation why you don't get "text book" results

 

[ajl_02]

Thanks for the reply. I will give it a go. Maybe to be sure I will put the cables into terminal block at the board and try to measure from the socket again. That way the cables won't be picking up any parallel paths in the fuse board. Just want to be sure as I want everything to be spot on for my NIC assesment. I have read somewhere on this forum before that NIC inspector flagged up a R1 + R2 result being higher than r1 value and said this was not acceptable. Would the results i got affect my assesment outcome??

 

[Edd]

Sounds like a possible figure of 8 circuit, when your testing at the board your testing a small loop possibly doing just one or two sockets Then fed from the smaller loop is a bigger one that goes off round all the other points and back.

 

[ackbarthestar]

To add to Malcolm and Edd.
Don't forget to zero your instrument every time you turn it on

 

[ajl_02]

That is what I was thinking. Looks like in going to break down the circuit and somehow make it back into one ring. As this would be unsatisfactory surely?? Would this need to be corrected before my nic assesment??

 

[malcolmsanford]

I'm not sure you do have a figure of 8 ring final to be honest, because your saying your getting uniform results at the socket face of 0.43ohms.

A figure of 8 ring would give you varying results around the circuit at the sockets

 

[ajl_02]

I see what you mean actually. I'm going to have a look into it further soon. Hope everything's turns out ok as need to cause as little disruption as possible. It's the in laws house so can't chase any walls and trunking is a no no. Got my assesment next month AI hope it turns out ok. Thanks for the help. Will post an update when done

 

[Edd]

I'm not sure you do have a figure of 8 ring final to be honest, because your saying your getting uniform results at the socket face of 0.43ohms.

A figure of 8 ring would give you varying results around the circuit at the sockets

Yer Your right,, it would start low and go up at the furvest point then back down. Intresteing fault.
My first port of call would be to start splitting the ring down into bits, anyway Let us know what you find.

 

[ackbarthestar]

hmmm.....
Surely a figure of eight interconnected loop between R1 in/R2 out and R1 out/R2 in will give you the same reading, or more or less, all the way round the rfc?
It will only increase to the physical centre of the rfc if R1 in/R2 in and R1 out/R2 out are connected.

So, I'm not so convinced that you have done the test wrong. The varying results will be when you loop test or use the long lead method

I would check your first readings again, end to end first.
and
1/ make sure the batteries are in good condition
2/ zero the instrument each time you perform the test
3/ Test at the terminals and not through the socket
4/ you have a good contact with the probes to the terminals

 

[SYKRAPS]

Split the ring at the furthest point and see if you have ring continuity still at the CU and at varying points, this will concur if there is a piggy back ring or not

 

[Farmelectrics]

the meter dosnt lie are the readings acceptable in relation to fuse size