Proving an 11kV cable to ensure dead

[bigswitch]

To prove an electricity distribution cable of 11kV dead, the cable is spiked using a spike gun with a blank cartridge. Are the circuit main earth(s)(CME's) left on or off whilst spiking? If the earths are at either end of the circuit (cable ends), do they both need to be on? Usually one cme is removed tio identify the cable with signal injection device........

thanks

 

[isquaredr]

I use this procedure, identify the cable to be worked on by signal injection. This is done by connecting a signal generator on 2-cores at one end (earth off), I then go and id the cable were the work is to be done, instruct the craftsman to attach the cable spiking tool whilst I go and remove the signal generator and replace the earth. When I return I spike the cable and procede with the work (after the issue of relevant safety document)

 

[bigswitch]

isquaredr thank you for that, so both earths SHOULD be on during spiking. I'm struggling with this as a code of practice Q&A paper states (of a particular DNO that am researching)that
"Q)After spiking a cable how would you remove the spiking gun?

A)replace the CME after spiking the cable and remove the spiking before cancelling SFT"

 

[isquaredr]

I would cancel the sft after spiking, issue the ptw and then remove the spiking gun.

 

[davidbeach]

There's a whole lot of terminology here that seems a bit foreign, probably all quite common in the IEC world. What are:
CME?
DNO?
SFT?
PTW?

In the OP, CME is called Circuit Main Earth, but what is that?

Also, what would be the point of "removing the spiking", the cable has been destroyed when it was spiked and has to be replaced anyway? Or is spiking something very different than what I'm picturing?

 

[itsmoked]

Maybe they just spike the soon to be opened/repaired splice?

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[bigswitch]

CME? Circuit main earth - a rated earthing device at an electricity distribution sub-station or on an overhead line(s). earths the conductor to be worked on for safety.
DNO? distribution network operator (UK term)
SFT?Sanction fot test (saftey document)
PTW? Permit to work (saftey document)

In the UK we spike high voltage electricity cables to prove that they are not live (dead), before we work on them, using a remote operation spiking gun....

http://www.acclesandshelvoke.co.uk/cablespiker.htm

Once the cable is spiked (from top through to the bottom it (cross sectionally)) and earthed back up it can then be worked on, obviously one would spike close to the point of work so the damage is repaired at the same time of the work (cable jointing etc)

 

[bigswitch]

isquaredr , thanks again.

May I just verify what you are saying.....

1)earths would be ON at both ends before spiking?

2)You would cancel the SFT with 'earths replaced'? Then issue a PTW 'to remove spiking gun, carry out straight joint' for example?

From the Q&A paper I was researching i.e.
"Q)After spiking a cable how would you remove the spiking gun?

A)replace the CME after spiking the cable and remove the spiking before cancelling SFT"
This suggested the earth(s) were OFF when actually spiking and only replaced afterwards, and before the sike gun was removed under the SFT???

Any ideas please?

 

[isquaredr]

bigswitch, I carryout spiking in the order quoted for 2-reasons
1. whilst the gun is being fitted to the cable to save time later I go and replace all earths and remove id equipment, when I arrive back to site the gun has been fitted and the cable ready for spiking
2. removal of the gun after spiking, I do this under a PTW as the gun at this point is connected to the primary conductors. I apreciate that this could be difficult to achieve in all circumstances (ie if more than one cable requires spiking) but it makes sense to do so if possible. If it was not possible to achieve I agree the gun would be removed under the SFT with "earths replaced".

There are no benefits in leaving the earths "off" before spiking.
You could have the scenario were the cable goes to a bottle end and so unable to id the cable by signal injection, in this case you would IR test the cable before and after spiking to confirm the correct cable has been spiked.