/ UK Power Networks / HSS 40 059
v1.0

Identification of Neutral Conductor on
LV Underground Cables

Owner
Name / P Vujanic
Title / Head of Safety Health and Environment
Signature
Date / 02 January 2018
Authoriser
Name / Dudley Sparks
Title / Operational Safety Manager
Signature
Date / 02 January 2018

This document forms part of the UK Power Networks Integrated Management System and compliance with its requirements is mandatory. Departure from these requirements may only be taken with the written approval of the above authoriser.

Revision Record
Version number / 1.0 / What has changed?
New procedure
Why has it changed?
Date published / 08/01/2018
Next review date / 08/01/2019
Prepared by / G Nichols/
D Daintree
Version number / What has changed?
Why has it changed?
Date published
Next review date
Prepared by
Version number / What has changed?
Why has it changed?
Date published
Next review date
Prepared by
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Contents

1.0Introduction and Purpose

2.0Scope

3.0Objectives

4.0References

5.0Definitions

6.0Responsibilities

7.0Records

8.0Process Detail

1.0Introduction and Purpose

This document explains the process required to identify the neutral conductor on an
LV underground cable.

2.0Scope

This document applies to all licence areas of UK Power Networks and to UK Power Networks Services

3.0Objectives

3.1To provide an approved method of identifying the neutral conductor core on an LV underground cable.

3.2To ensure the safety of UK Power Networks employees, its contractors and the public.

3.3To reduce the risk of damage to UK Power Networks’ assets.

3.4To reduce the risk of damage to assets owned by other parties.

3.5To minimise the liability of UK Power Networks or its contractors.

4.0References

DSR 01 018 / Identification of LV cables
DSR 01 007 / Identification of HV cables
DSR 01 016 / Process on how to ensure low voltage customers have correct polarity and phase rotation
EDS 06-0004 / Earth Fault Loop Impedance Requirements
LV Jointing Manual
HSS 40 059a / The use of ELI and clamp ammeter example
HSS 40 059b / The use of Megger Cable identifying Generator CI TX example
HSS 40 059c / The use of Ariadna cable identifying Generator CI TX example

5.0Definitions

Unidentified cable / A cable whose ownership, circuit designation, identity or purpose cannot be determined.
Abandoned cable / A disconnected cable that is no longer required for any future use.
Idle cable / A disconnected cable, which may be required for future use
Process Manager / A descriptive term to describe a manager, above middle management grade, who has responsibility for a particular process or the distribution network in a specific geographical area. This term has been used in preference to the current position names, as these changes relatively frequently.

6.0Responsibilities

6.1It is the responsibility of process managers, to ensure that their staff and contractors comply with this procedure.

6.2It is the responsibility of all UK Power Networks staff and contractors working on behalf of UK Power Networks, to comply with this procedure.

7.0Records

7.1The liability and indemnity letter (HSS 40 029a) should be retained for a period of two years.

8.0Process Detail

8.1Identifying neutral conductor when at least one core is live:

How to identify the neutral on a multi-cored cable that has lost one or more live phases but still has at least one of the cores live.

This procedure is to be used in order to prove the neutral on a cable that has lost a phase

After opening the cable and finding a dead phase, to correctly identify the neutral, the following two checks will need to be carried out.(Note: due to the nature of the type of fault, using test lamps to prove the neutral will not work as you will get a 230v light between live and neutral and a load light between live and the dead phase, often to the same intensity as a normal 230v light.)

1.Identify cable in line with DSR 01 018 identification of LV cables

2.Using an Earth Loop Impedance tester go between a live core and one of the dead ones, note the reading, carry out the same test between the same live core and the other dead core. The reading between the live phase and the neutral will be a low reading generally around the 0.13-0.23 ohms region, the result between the live phase and the dead phase will be very high and sometimes will not register on the ELI tester.

3.Using a Clamp ammeter place the clamp around one of the dead cores, make a note of the reading and repeat with the other dead core. The clamp meter will register a current on the neutral whilst the dead core will display no current flowing.

As long as both tests can be carried out and you are happy to proceed, cut the dead core that has the highest ELI reading and no current flowing on it. If the results are not conclusive then follow section 8.2 below which details what to do if no cores are live.

8.2Identifying neutral conductor where no cores are live:

How to identify the neutral conductor on a multi-cored cable that has lost all live phases.

It must be recognised that the point of reference (the cut-out) on this test could have an incorrect polarity already existing. This unlikely risk will be mitigated by the polarity checks post energisation. Any control measures should be noted on the point of work risk assessment that are required depending on the activity-taking place.

1.Identify cable in line with DSR 01 018 identification of LV cables

2.Prepare cable for testing at the location in which the neutral is being identified

3.Confirm current status of cable by completing full test using approved test lamps

4.Select an appropriate test point in which the signal can be injected via an approved instrument. This can be a customer’s cut-out, street furniture or LV equipment where the neutral can be clearly identified.

5.Select an approved neutral conductor identifier and use the procedure in the relevant appendix to prove the neutral.

6.Carry out identification of neutral conductor and clearly mark up the neutral core with identification tape. Repeat identification of the neutral to ensure the correct conductor is taped.

7.Carry out jointing activities as per job requirements

8.Once the circuit has been energised, carry out testing in accordance with DSR 01 016 Process on how to Ensure Customers have Correct Polarity and Phase Rotation.

This printed document is valid at 09/12/18, check after this date for validity.
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