R1 and R2 Maximum value

[Golden_Boy]

Am I right in thinking that for any ring circuit the maximum value that r1+r2 can be is 1/2 the loop reading on the phase + 1/2 the loop reading for the cpc ( measured at the CU ) Or has my maths let be down?

 

[Mr Mark Sparks]

the r1 r2 for a ring should be live-live + cpc-cpc devided by 4

so you are on the right lines your terminoligy is a bit out

ideal reading not max
continuity not loop

 

[Guest123]

Also depends if 2.5/1.5 as in T+E, or 2.5/2.5 as in singles.

 

[Risteard]

(R1+R2) = (Line loop plus cpc loop)/4.

Doesn't matter what csa cpc is in relation to Line conductor as you are adding the two and dividing the lot by four.

In a ring final circuit you are effectively halving the length of the conductors and doubling the cross-sectional area.

 

[Guest123]

(R1+R2) = (Line loop plus cpc loop)/4.

Doesn't matter what csa cpc is in relation to Line conductor as you are adding the two and dividing the lot by four.

Of course it matters......Will the end to end readings not be different for a ring circuit with a 1.5mm cpc and a 2.5mm cpc.

In a 2.5/1.5 ring the yardstick is 1.67 times the the line/neutral end to end value for the cpc.

 

[Mr Mark Sparks]

hey len
yeah the end to end readings will vary depending on the ratio of the cpc size
but its still r1+r2 divided by 4

.20r1 + .34r2 /4 = .08 (2.5/1.5)

.20r1 + .20r2 /4 = .10 (2.5/2.5)

i suspect we all know what we mean but its getting lost in "translation"

 

[ian.settle1]

Of course it matters......Will the end to end readings not be different for a ring circuit with a 1.5mm cpc and a 2.5mm cpc.

In a 2.5/1.5 ring the yardstick is 1.67 times the the line/neutral end to end value for the cpc.

But what if the ring is wired in 4mm T& E or 4mm singles?

 

[Risteard]

As Mr Mark Sparks says it is ALWAYS (R1+R2) = (r1+r2)/4 for a ring final circuit. As I say, it makes no difference what csa the cpc is as the equation is still dividing the total of your end-to-end loops by four.

 

[Guest123]

Seems I misinterpreted the op.

Apologies.

 

[Risteard]

Seems I misinterpreted the op.

Apologies.

Don't worry. It may be me that misinterpreted it!

 

[Golden_Boy]

Thanks .... I was right and my school algebra lessons DID sink in LOL

 

[platty1005]

The max R1+R2 for a ring final circuit is the maximum value measured during step 3 of the 3 step test. See OSG page 80 - 10.3.2 The formula quoted by others (r1+r2)/4 is only correct for sockets wired on the ring. Spurs will show a higher reading hence the need for the 3 step test to identify spurs and to confirm the ring is correctly wired.

 

[telectrix]

IMO the (r1+r2)/4 is only a guide as to what you should get for R1+R2. same as for example if you had a circuit of 10m 2.5/1.5, you would expect R1+R2 to be around 0.2ohms, using the resistvity table 9A OSG. the values entered on a certificate must be measured values.