16th Edition (reference only) – NOW superseded by the 17th Edition IEE Regulations.
 chapter 1 The IEE Regulations chapter 2 Installation Requirements and Characteristics chapter 3 Installation Control and Protection chapter 4 Cables, Conduits and Trunking chapter 5 Earthing chapter 6 Circuits chapter 7 Special Installations chapter 8 Testing and Inspection chapter 9 Data cabling and Networks
 Inspection and Testing
 8.1 - Introduction 8.5 - Insulation tests 8.2 - Inspection 8.6 - Earth testing 8.3 - Testing sequence 8.7 - Test instrument requirements 8.4 - Continuity tests 8.8 - Supporting paperwork
 8.4.1 - Protective conductor continuity 8.4.2 - Ring final circuit continuity 8.4.3 - Correct polarity 8.4.4 - Measurement of R1 + R2

8.4.4 - Measurement of R1 + R2

In {5.3.6} and in {Table 5.5} we considered the value of the resistance of the phase conductor plus that of the protective conductor, collectively known as (R1 + R2). This can be measured with a low resistance reading ohmmeter as described in item 1 of {8.4.1} (strictly the phase, rather than the neutral resistance is being measured here, but there should be no difference) and will be necessarily at the ambient temperature which applies at the time. Multiplication by the correction factor given in {Table 8.6} will adjust the measured resistance to its value at 20°C.

 Table 8.6 - Correction factors for ambient temperature Test ambient temperature °C Correction factor 5 1.06 10 1.04 15 1.02 20 1.00 25 0.98

These will be the resistance values at 20°C and must be adjusted to take account of the increase in resistance of the conductor material due to the increased temperature under normal operating conditions. This second correction factor depends on the ability of the insulation to allow the transmission of heat, and values will be found in {Table 8.7} for three of the more common types of insulating material.

An alternative method for measuring (R1 + R2) is to carry out a loop impedance test at the extremity of the final circuit and to deduct the external loop impedance for the installation (Ze). Strictly it is not correct to add and subtract impedance and resistance values, but any error should be minimal.

 Table 8.7 - Temperature correction factors for insulation Insulation type Correction factor - Bunched or as a cable core Not bunched or sheathed cable p.v.c. 1.20 1.04 85°C rubber 1.26 1.04 90°C thermosetting 1.28 1.04