R1+R2 Resistance per Metre of Copper Conductors

by Steve on March 25, 2009

Reference- Resistance of Copper Conductors

Electrical testing and measuring circuits for r1 r2 test values.

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r and R
r1, r2 and rn are the end to end ring circuit readings.

R1 is the maximum measured resistance of the line conductor for a circuit.

R2 is the maximum measured resistance of the cpc for the circuit.

R1+R2 is the test reading value of the two resistances added together.

Ring Circuits

Testing of a ring main circuit requires the creation of a ‘super loop’ for verifying and measuring the R1+R2 values.    This involves joining the opposite ends of the live and earth conductors for testing.  Then the R1+R2 test values for a ring main circuit (when measured at each socket outlet on the ring) should be r1 plus r2 divided by 4.

r1+r2/4 = R1+R2 for socket outlets on the ring.

Note that spurs from the ring will give higher readings.  See Chris Kitcher’s video on Ring Main Testing.

Smaller CPC
The r2 testing resistance value for a smaller sized cpc in a twin and earth cable (2.5 with 1.5) can be calculated  by r1 x 1.66.

Radial Circuits- Resistance per metre for copper conductors

You can use this reference page online when verifying your R1+R2 test  measurements without having to dig out your On-site Guide.

Here are some resistance values for the most commonly used cable combinations:

Line                           CPC                      ohm/mtr

1                                      1                            0.036        ie.   x 1 metre = 0.036 ohms

1.5                                   1                            0.030

1.5                                   1.5                         0.024

2.5                                   1                             0.025

2.5                                   1.5                         0.019

2.5                                   2.5                         0.014

4                                       1.5                          0.016

4                                       2.5                         0.012

4                                       4                             0.009

6                                       2.5                         0.010

6                                       4                             0.007

6                                       6                             0.006

10                                    4                             0.006

10                                    6                              0.005

10                                    10                           0.003

16                                     10                           0.003

16                                     16                           0.002


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