Ring r1r2 test

[Rob_the_rich]

 There is no furthest point on a final ring circuit, as the circuit could be broken at any point to test the R1+R2.

Are you sure Manator?

With T&E, R1+R2 must be done from the origin of the supply. The end to end tests and the L & N cross connected tests can be done anywhere on the ring.

Take a sample socket at or near a spur and cross connect at that point. The R1+R2 of the spurred socket would be lower than if cross connected at the origin because the further you go from the Xcon point, the higher the resistance is.

I started last night to put a spreadsheet together to try and test this but it is very confusing with parallel resistances etc. and my limited spreadsheet skills. I might try again when I have time.

Edit; how do you unquote a post? or cancel it? There is a cancel button when editing, but not when posting.

 

[Andy™]

R1R2 on a ring can be done anywhere. its sometimes easier to link L-E at a socket than at the board

 

[Manator]

R1R2 on a ring can be done anywhere. its sometimes easier to link L-E at a socket than at the board

I have had to do this on occasion when the earths in the consumer unit are not matched to the breaker.

Rob, you are right, it should be done at the origin and there is no excuse if it is for initial verification. However as I have said to those who I have put through the 2391, it does not matter where you start testing as long as the testing is carried out properly.

 

[NozSpark]

when you do the cross connection R1+R2 tests on a ring your readings will be the same at every point on the ring (except for any spurs), any readings that you take at a spur will be the sum of the ring R1+R2 and the R1+R2 of the spur cable whether this is at the next socket along or if it's 1/2 way around the ring from your cross connections

 

[apprentice87]

Exactly...

john..

 

[James1978.]

The fault path back to the origin, which I interpret as the r1r2 is different for a spur of a ring main depending where you spur of. You are I believe allowed to take a spur directly from a 32amp breaker (yes I know it seems odd as I think it's the same as a 16a radial) which would have a greatly lower fault path than a spur half way around the ring (say feeding a shed)

 

[kerching]

I find that a lot of people are not aware of the differences between R1,R2, Rn, r1,r2 & rn

or am I just talking a load of Rs?

 

[James1978.]

when you do the cross connection R1+R2 tests on a ring your readings will be the same at every point on the ring (except for any spurs), any readings that you take at a spur will be the sum of the ring R1+R2 and the R1+R2 of the spur cable whether this is at the next socket along or if it's 1/2 way around the ring from your cross connections

Nozspark that's exactly what I mean

 

[apprentice87]

Er. no, Kerching, I think you are exactly right.

Following on from this, those that do not know, obviously do not seem to understand the reason for the various dead tests, or, what tests they should be doing and why..

john..

 

[apprentice87]

The fault path back to the origin, which I interpret as the r1r2 [It is R1 +R2] is different for a spur of a ring main depending where you spur of. [No it is not] You are I believe allowed to take a spur directly from a 32amp breaker (yes I know it seems odd as I think it's the same as a 16a radial) which would have a greatly lower fault path than a spur half way around the ring (say feeding a shed) [Wrong, it would not matter if you took the spur 1 millimetre from the end of the ring or halfway along]

 Is COMPLETELY different from;

when you do the cross connection R1+R2 tests on a ring your readings will be the same at every point on the ring (except for any spurs), any readings that you take at a spur will be the sum of the ring R1+R2 and the R1+R2 of the spur cable whether this is at the next socket along or if it's 1/2 way around the ring from your cross connections

Which is exactly right..

john...

 

[Rob_the_rich]

when you do the cross connection R1+R2 tests on a ring your readings will be the same at every point on the ring ...

According to my spreadsheet this is not true. However, the calculated readings I got are within less of a range than I originally thought. I assumed the difference between maximum and minimum would be greater than they turn out to be. Even if you put in the resistance for a 1mm CPC, for a 50m ring there is only .06 ohms difference. So practically speaking you are correct :B-

Would appreciate someone checking it though.

View attachment ring calculations r1r2.xlsx

 

[Andy™]

it will be the same. put it this way, you have a circle. no matter which point you are, its the same distance to the other side

 

[NozSpark]

I don't understand why you are using the distance between the points in your calculations..

You need to draw this out to understand it properly...

 

[Lusk]

According to my spreadsheet ............

If you're saying that the resistance increases from the inter-connection to the furthest point, you are correct (for r1<>r2).

But like you say, the increase is small, you'd just lose it in measurement error.

I've got a mathematical proof somewhere if you're really interested!!!

 

[NozSpark]

His spreadsheet is wrong!!!

 

[Manator]

According to my spreadsheet this is not true. However, the calculated readings I got are within less of a range than I originally thought. I assumed the difference between maximum and minimum would be greater than they turn out to be. Even if you put in the resistance for a 1mm CPC, for a 50m ring there is only .06 ohms difference. So practically speaking you are correct :B-

Would appreciate someone checking it though.

View attachment 6546

I have had a look at your spreadsheet, I think what it does do is prove the theory right about what you would expect at each socket. However the first point should be at the initial R1+R2 reading at the CU.

What your meter would do unless it can read to 4 or 5 decimal places is to round up or down. If we did this you would find that all your points on the circuit would be almost identical.

 

[Rob_the_rich]

I have had a look at your spreadsheet, I think what it does do is prove the theory right about what you would expect at each socket. However the first point should be at the initial R1+R2 reading at the CU.

What your meter would do unless it can read to 4 or 5 decimal places is to round up or down. If we did this you would find that all your points on the circuit would be almost identical.

The first point is at the CU. Thanks for checking it Manator.

I don't understand why you are using the distance between the points in your calculations..

You need to draw this out to understand it properly...

It is a ring with 7 sockets spaced equally with the CU being where the X connection is. couldn't think of any other way to do it.

As I said, I expected a greater difference between max and min values, hence my earlier posts. Every day is a schoolday.

If you're saying that the resistance increases from the inter-connection to the furthest point, you are correct (for r1<>r2).

But like you say, the increase is small, you'd just lose it in measurement error.

I've got a mathematical proof somewhere if you're really interested!!!

Not any more mate, I'm done.

 

[NozSpark]

Rob... if you expand the interconnected L-E circuit you get a circle with one half being the L and the other being the E when you do the tests you test at points 180deg apart on that circle so the resistance measured at any point will always be the same.

Assuming it's a proper ring without spurs, that is

 

[Rob_the_rich]

Rob... if you expand the interconnected L-E circuit you get a circle with one half being the L and the other being the E when you do the tests you test at points 180deg apart on that circle so the resistance measured at any point will always be the same.

Assuming it's a proper ring without spurs, that is

At the CU one half is L and the other is E

At point 1, there are 2 resistances you are measuring, one is 7/8 L:and 1/8 E, the other is 7/8 E and 1/8 L. You then combine these parallel resistances using 1/Rt=1/R1+1/R2. This is how I worked out the spreadsheet.

 

[NozSpark]

No..... draw it out,, just a loop of the L & E

It ends up being just one great big circular conductor