Cable Spiking High Voltage Cables – UK Power Networks

Published 14 Nov 2018

Cable Spiking High Voltage Cables – UK Power Networks

• Information Courtesy – UK Power Networks

8.13        Procedure for Spiking Cables

Following the identification of a cable, the cable will then need to be spiked using a cable spiker to ensure that it is not Live at HV. The following procedure shall be followed:

1. If the process has not already necessitated a Sanction-for-Test, then a SFT must be obtained from Control (A SFT cannot be issued for idle or abandoned cables that are not part of a network, as Circuit Main Earths cannot be applied)
2. If the cable has been identified by signal injection, it is not necessary to disconnect the instrument and re-apply the Earth
3. The consent of the Control Engineer must be obtained prior to spiking
4. Spike the cable
5. Call Control and ask if any alarms have been received
6. Before the spiking gun is removed, at least one of the verification tests, given below, must be conducted
7. Following a positive result of the verification test, the earths will be re-applied and remain applied whilst the spiking gun is removed under the SFT and under the Personal Supervision of the recipient of the SFT. (this does not preclude the option of the SAP to issue a PTW to remove the spike gun)
8. Furthermore, under the same SFT and following the removal of the spiking gun, the cable may be opened and stripped for phase colour tests to be made under the Personal Supervision of the recipient of the SFT (this does not preclude the option for the SAP to issue a PTW to open and strip the cable)
9. SFT to be cancelled and a Permit-to-Work shall be issued for work to commence on the cable.

Injected Signal Strength Verification

Listen to the signal on either side of the spiking gun.

The signal strength on the side on which the signal is being injected should be distinctly louder than that on the furthest side.  This is because the spike driven into the cable will be providing a short-circuit route for the signal.  Therefore much less signal, if any, will flow to the end of the cable where the circuit main earth has been applied.

Verification by Insulation (Megger) Testing.

Prior to spiking, remove all the Earths and megger the cable.  The cable can be tested between phases and between phase to Earth.

The tests should show healthy insulation values.

After spiking, test the cable again.  The results should show a faulty cable, thus proving that the correct cable has been spiked.

Why Must Control be Contacted Before Spiking?

It is a requirement of DSR 5.9.2.

The consent of the Control Engineer must be obtained before spiking, to alert their attention that an incorrect spiking may have occurred, if an alarm is received.

The Control Engineer also has a final opportunity to prevent the spiking, if a feeder trips on the network in that vicinity.  The circuit may be required to support the load and so the job may have to be postponed.

Why Must Control be Contacted After Spiking?

It is a requirement of DSR 5.9.2.

The Control Engineer must be contacted after spiking, so that a check may be made for any alarms that could be linked to the spiking.  The Control Engineer may need to check with other Control Engineers.  This is because there have been occasions when cables have been incorrectly spiked and the alarm has been received and accepted by another Control Engineer and not communicated to the Control Engineer dealing with the cable spiking.

8.14       Spiking Requirements of Circuits Comprising of Single Core Cables

In normal circumstances the spiking gun should be applied such that all three cores are spiked.  However in the following circumstances it is essential that all three cores are spiked:

• 11kV Networks with Arc Suppression Coils
• 11kV Networks fed from Unganged Fuses
• Pot / Stop Ended Circuits

General

There may be occasions [excluding (i), (ii) or (iii) above] where it is only required to work on one or two of the single core cables.  It would therefore be undesirable to spike and damage all three.

If only one or two of the single core cables are to be spiked, then insulation tests before and after spiking shall be conducted, to confirm that the correct circuit has been spiked.  It will be necessary to use an instrument that applies a sufficiently high voltage, to detect the damaged caused by the spiking. This is necessary, as the single core cables may be completely severed by the spike and may appear as an open circuit (and therefore healthy), if the voltage applied by the instrument is too low.

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8.15       Re-location of point of work

Following the positive identification and spiking of a cable, it may be necessary to change the point of work after issuing a Permit to Work e.g. when dampness testing. This may be done, without reference to the Permit issuer, and without the need for further spiking, provided that the Permit holder can physically trace the cable by means of a running noose from the initial point of work, to the new point of work.

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