MATERIALES ELECTORALES

Refer to Appendix A19(b) and A19(c).

Earth connections Current clamp Voltage clamp Electrode under test

A19(a)

Measurement of earth electrode resistance

(i) This method uses an Earth clamp-based tester without the need to disconnect

the Earthing Conductor.

(ii) This method is used when there are a number of Earth Electrodes and it is not

possible to use Method 1.

(iii) The larger the number of Earth Electrodes, the closer the measurement would

be to the electrode under test as the measurement is the Earth Electrode under test in series with all other Earth paths in parallel.

(iv) It is important to highlight that for this method to be effective, there must be a

loop resistance to measure and the Earth mass must be part of the measurement.

A19(b)

A19(b) Measurement of Distribution

Company supply impedance (Ze)

Main Earthed Equipotential Bonding

External Earth Loop Impedance Tester Main Earth

Terminal Main Distribution Board

To Earth Electrode

A Earth Bar Test Link removed and Earth Electrode Connection removed A MCCB + E/F MCCB + E/F Notes:

1. Caution: this test is carried out under live conditions but with the main isolator secured in the off position.

2. Ze may be measured directly at the Supply Intake with a specialist Earth Loop Impedance tester. Such devices apply a resistance (typically 10 ohms) between a phase conductor and the earth conductor of the incoming supply. The test draws a current of around 20A but is only applied for a few cycles (e.g. 40ms). The device measures the drawn current and divides this into the measured supply voltage to give the loop impedance (the test resistance applied by the device is subtracted).

3. As an alternative Ze may be calculated from measurement of the total earth fault loop impedance measured within the installation (see A19c) using the formula:

ZS = Ze + ZR1+R2

Where:

Zs = total Earth Fault Loop Impedance Ze = Distribution Company supply impedance

ZR1+R2 = impedance of the longest circuit in the Installation, taken by measuring a circuit

phase conductor impedance R1, and the same circuit’s Earthing Conductor impedance R2.

4. For further advice see reference book “ Advanced Testing Technique”.

Note 1: caution: this test is carried out under live conditions but with the main

isolator secured in the off position.

Note 2: Ze may be measured directly at the Electricity Intake with a specialist

Earth Loop Impedance tester. Such devices apply a resistance (typically 10 ohms) between a phase conductor and the earth conductor of the incoming supply. The test draws a current of around 20A but is only applied for a few cycles (e.g. 40ms). The device measures the drawn current and divides this into the measured supply voltage to give the loop impedance (the test resistance applied by the device is subtracted).

Note 3: as an alternative Ze may be calculated from measurement of the total

Earth Fault Loop Impedance measured within the Electrical Installation (see A19(c)) using the formula:

Where:

Zs = total Earth Fault Loop Impedance Ze = Distribution Company supply impedance

ZR1+R2 = impedance of the longest circuit in the Installation, taken by measuring a circuit phase conductor impedance R1, and the same circuit’s Earthing Conductor impedance R2.

Note 4: For further advice see reference book “ Advanced Testing Technique”.

Main Earthed Equipotential Bonding

External Earth Loop Impedance Tester Main Earth

Terminal Main Distribution Board

To Earth Electrode

A Earth Bar Test Link removed and Earth Electrode Connection removed A MCCB + E/F MCCB + E/F Notes:

1. Caution: this test is carried out under live conditions but with the main isolator secured in the off position.

2. Ze may be measured directly at the Supply Intake with a specialist Earth Loop Impedance tester. Such devices apply a resistance (typically 10 ohms) between a phase conductor and the earth conductor of the incoming supply. The test draws a current of around 20A but is only applied for a few cycles (e.g. 40ms). The device measures the drawn current and divides this into the measured supply voltage to give the loop impedance (the test resistance applied by the device is subtracted).

3. As an alternative Ze may be calculated from measurement of the total earth fault loop impedance measured within the installation (see A19c) using the formula:

ZS = Ze + ZR1+R2

Where:

Zs = total Earth Fault Loop Impedance Ze = Distribution Company supply impedance

ZR1+R2 = impedance of the longest circuit in the Installation, taken by measuring a circuit

phase conductor impedance R1, and the same circuit’s Earthing Conductor impedance R2.

4. For further advice see reference book “ Advanced Testing Technique”.

A19(c)

A19(c) Measurement of total Earth Fault Loop

Impedance (Zs)

Final Distribution Board

Main Distribution Board

CECs remain connected Bonding Conductors from FDB RCD RCD to light

(bulb removed from pendant) to switch (must be ON)

to Test Instrument Earth Electrode

Incoming Supply Cable

Note 1: caution: this test is carried out under live conditions with the circuits under

test energised but no load is connected.

Note 2: a specialist instrument is used which measures the total Earth Loop Impedance Zs using a similar principle as described in A19(b). The instrument must not operate any RCD in circuit.

Note 3: the instrument may be directly connected to a socket-outlet (using the test plug provided) and should be used at the farthest point on a radial circuit or the mid point of a ring circuit. Alternatively, the instrument may be used at an Accessory connection point (e.g. lighting ceiling rose) with the appropriate test probes.

190 The Electricity Wiring Regulations (Third Edition)

A19(d)

A19(d) Circuit continuity, (R1+R2) and

(R1+Rn) tests

Radial Circuits and lighting Circuits:

1. This method tests the combined phase and Earth resistance (R1+R2) and phase and neutral resistance (R1+Rn) for each Circuit by applying short leads (not at the same time) at the Distribution Board, and measuring from the terminals of the farthest connection point or socket-outlet.

2. The polarity can be checked at each Accessory (i.e. only one of the live / neutral terminals should show continuity to Earth, and there should be no continuity between live and neutral). 3. If an Accessory has been wired incorrectly from another phase

or neutral conductor, the test will not work (e.g. crossed Circuits or “borrowed neutral”).

4. For lighting Circuits the light switches should be ON to test the wire through the switch.

5. For metal conduit Circuits the CEC at the conduit/ back-box should be disconnected in order to accurately measure R1+R2.

Shorting Lead R1+Rn R Y B R Y B R Y B Final DB A R Y B R Y B R Y B Final DB A Check polarity (neutral unearthed)

A19(d) Circuit continuity, (R1+R2) and (R1+Rn) tests

Check polarity and record R1+R2 (and no continuity to neutral) Shorting Lead R1+R2 Record R1+Rn (and no continuity to Earth / CEC) R1+Rn to switch (must be ON) “borrowed neutral”

A19(d) Shorting Lead R1+Rn R Y B R Y B R Y B Final DB A R Y B R Y B R Y B Final DB A Check polarity (neutral unearthed)

A19(d) Circuit continuity, (R1+R2) and (R1+Rn) tests

Check polarity and record R1+R2 (and no continuity to neutral) Shorting Lead R1+R2 Record R1+Rn (and no continuity to Earth / CEC) R1+Rn to switch (must be ON) to lamp holder “borrowed neutral” >100MΩ

A19(d) Continued...

1. For Ring Circuits, the test consists of two stages:

(a) the measurement of end to end resistance of each conductor.

(b) the measurements of R1+R2, R1+Rn and checking there are no ‘bridges’ in the ring.

Note 1: these tests are carried out on dead Circuits. The main isolator must be secured in the off position.

Note 2: for new Electrical Installations, these tests should be carried out when

Accessories are in position but prior to energising the Electrical Installation.

Note 3: Circuit continuity tests must be measured for all Circuits and the resistance

values recorded on the test report, see Appendix A20(d).

A19(d)

A19(d) Continued...

2. For part 1(a), measurement of the phase and neutral loops should give equal values. The Earth loop may be of slightly higher resistance if it is wired with a smaller conductor.

3. For part 1(b), measurement at any point on the ring between phase and neutral gives ½ the value measured in part 1(a). 4. To measure R1+Rn for a Ring Circuit, the two phase and

neutral conductors from the ring are cross connected. The measurement at any point on the ring between phase and neutral should give ½ the value measured in part 1(a). If equal resistances are not observed around the ring then this indicates the presence of a bridge or wrong cross-connections at the FDB end of the Circuit.

5. To measure R1+R2 for a Ring Circuit the two phase and Earth conductors from the ring are cross connected. The readings at each point in the ring may vary slightly for a very long circuit (since the CEC is a smaller cross-section).

6. The highest value obtained represents the maximum R1+R2 value for the Circuit, and should be recorded on the test form. A19(c) continuation

Ring circuits continuity:

FDB N L FDB N L FDB L E A19(e) A19(d) (R1 + R2) (R1 + Rn) Conductor end to end test

A19(d)A19(e)