Discuss R1 and R2 Maximum value in the Periodic Inspection Reporting & Certification area at ElectriciansForums.net

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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?
 
(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.
 
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(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.
 
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";)
 
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.
 
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.
 
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.
 

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