Can't figure ring final r1 + r2 divided by 4

[KeenPensioner]

Hi...keen amateur here......don't crucify me for asking!! I understand Ohm's law and I understand the mechanics of measuring end to end on ring final and then joining incoming live to outgoing neutral etc, and I know that this configuration gives a figure of 8 (in fact can be straightened to give a complete circle) but I can't figure out the "calculated method" of dividing by (r1+r2)/4....why?
If you meter across the mid point of the "circle" then yes...
if K= r1+r2 (the complete circle) then...since in parallel...
1/R = 1/(K/2) + 1/(K/2) which simplifies to 1/R = 4/k, then R=K/4....(r1+r2)/4........but what happens if you measure across the circle at any other point other than the mid point?

 

[westward10]

0.09 Tel

 

[telectrix]

correct. it was a sticking "0" key on the laptop, honest.

 

[KeenPensioner]

Thanks every body.....I understand it now

 

[johnduffell]

the resistance at the CU will be approximately 0.94x that at the midpoint, depending on the accuracy of the cable CSAs.

... Edited in case I'm being silly!

 

[Wilko]

Thanks every body.....I understand it now

Now you'll have to explain it to me

 

[KeenPensioner]

Hi...keen amateur here......don't crucify me for asking!! I understand Ohm's law and I understand the mechanics of measuring end to end on ring final and then joining incoming live to outgoing neutral etc, and I know that this configuration gives a figure of 8 (in fact can be straightened to give a complete circle) but I can't figure out the "calculated method" of dividing by (r1+r2)/4....why?
If you meter across the mid point of the "circle" then yes...
if K= r1+r2 (the complete circle) then...since in parallel...
1/R = 1/(K/2) + 1/(K/2) which simplifies to 1/R = 4/k, then R=K/4....(r1+r2)/4........but what happens if you measure across the circle at any other point other than the mid point?

Figured it out..see image...attachedView attachment 50817View attachment 50817

 

[KeenPensioner]

Figured it out....this image says it all..

 

[UNG]

Hi...keen amateur here......don't crucify me for asking!! I understand Ohm's law and I understand the mechanics of measuring end to end on ring final and then joining incoming live to outgoing neutral etc, and I know that this configuration gives a figure of 8 (in fact can be straightened to give a complete circle) but I can't figure out the "calculated method" of dividing by (r1+r2)/4....why?
If you meter across the mid point of the "circle" then yes...
if K= r1+r2 (the complete circle) then...since in parallel...
1/R = 1/(K/2) + 1/(K/2) which simplifies to 1/R = 4/k, then R=K/4....(r1+r2)/4........but what happens if you measure across the circle at any other point other than the mid point?

Using live and neutral will give R1 + Rn not R1 +R2

 

[KennyKen]

So glad we don’t use Rings in Aus.