Calculating r1 from R1 + R2

[Mike Blair]

Confused my self calculating r1 or 21 from R1+R2 on a ring circuit did this a while back and compared calculations with measurements to see the differences. but tried the other day think i have muddled the equation! or maybe because its monday haha can someone show me an example

 

[Leesparkykent]

For example you have an R1+R2 of 0.33ohms

0.33x4=1.32

1.32/1.64=0.80 for r2

1.32-0.80=0.52 for r1

Edit: should of added this is for 2.5mm cable with 1.5mm CPC.

 

[The Ghost]

Where did you get 1.64 from?

 

[Deleted member 72666]

I think he meant 1.67.

 

[The Ghost]

Thats what I thought 1.67 it comes to the same anyway.

 

[Wilko]

My inner Sheldon just can't resist ... I got r1=0.495 and r2=0.825 ... Probably why I've got no mates. Or work.

 

[Mike Blair]

so for a r1 and r2 i got 1.12 in the real world

calcultion is
r2 2.74

r1 = 1.74

seems high

 

[Mike Blair]

shouldnt i be deviding by 4?

 

[Leesparkykent]

LOL, yes I meant 1.67.....It was well past my bed time when I posted that last night

 

[Wilko]

Hi Mike, is this R1+R2=1.12 ?

 

[Leesparkykent]

so for a r1 and r2 i got 1.12 in the real world

calcultion is
r2 2.74

r1 = 1.74

seems high

That would indicate a circuit length of 230-240 meters.

 

[The Ghost]

so for a r1 and r2 i got 1.12 in the real world

calcultion is
r2 2.74

r1 = 1.74

seems high

shouldnt i be deviding by 4?

Errm can you show your maths on that answer?

 

[Mike Blair]

sorry guys my zs was 1.12 i dont do as much testing as i should be tbh drives my nut in

 

[Mike Blair]

ok so say if my zs was 1.32

ze was 12

needed to find r1 and r2

theoretically what would it be isnt it devide by 4 to R1+R2?

 

[Leesparkykent]

R1+R2= (r1+r2)/4

Zs=1.32

Ze=0.12

1.32-0.12=1.2

1.2x4=4.8

4.8/1.67= 2.87

4.8-2.87= 1.93

r2=2.87 and r1=1.93

Now using r1 and r2 figures

2.87+1.93=4.8

4.8/4=1.2

This is where your getting confused with multiply and divide

 

[The Ghost]

theoretically what would it be isnt it devide by 4 to R1+R2?

Go and look at post 2 except substitute 1.64 for 1.67. Then read and re read until it sinks in also look at GN3 around ring final circuit testing. It is explained perfectly in there. But yes you are right "little r1+little r2"/4 should = R1+R2 I presume you mean Ze was 0.12? I mean you do know that little r1 and little r2 and little rn are the end to end measurements on ring yes? Sorry in advance if that sounds a bit rude it is not meant to be.

 

[Wilko]

Hi Mike, apologies for stating the bleeding obvious ... this RFC can't run a 32A breaker due to Zs > 1.1 ohms,

 

[Toneyz]

I hope your not trying to find r1 + r2 from loop testing for the cert