How do the DNO cut live service cables?

[ahuman]

I could tell you but then I'd have to ....

Busy at the mo, I'll tell you tonight, but an eaelier poster had it about right

I'm waiting too. wondering if they need to work on my "live" meter shift?

 

[westie101]

Sorry long day

PILCSTA/PILCSWA

Remove outer hessian covering to expose the armors, carefully cut these with a junior hacksaw.
Remove over the length required and fasten down with PVC tape

Remove under hessian/bitumen covering using heat & wipes to expose lead serving

Fit a bypass bond across the lead to be removed

Remove lead with a circumferential cut at each end and by "cutting" along the length with an insulated hack knife.
http://www.clydesdale.net/view_products_02.asp?productID=170&siteIndexID=2&sectionIndexID=23

Secure each end of the papers with tape and remove

Shroud all exposed earthed metal work with non insulating material

This exposes the cores.
To cut use a junior hacksaw with a insulated insert between cores and cores & neutral to prevent cutting more through adjacent insulation.

CNE/scne service cables

Remove outer PVC sheath

Carefully lift neutral (and earth wires if SCNE) away from core insulation with a small screwdriver or wedge.
Do enough to get 50% away and cut them with side cutters one at a time as they are cleared from the core.

Connect the cut conductors together with screw connectors with a piece of cable between
Do the same with the remaining 50%
(for SCNE treat the neutral & earth separately)

Shroud all exposed earthed metal

Cut core or remove insulation.

Simples

Oh and this can only be done with the cable horizontal and clear of any obstruction

 

[westie101]

To be classed as competent to do that a jointer will undergo 6 weeks of workshop training, followed by 6 months on-job just to be authorised work on service cables.

Mains cables require a further session in the workshop and on-job training

Followed by tri-annual retesting to retain the authorisation

 

[stillp]

Shroud all exposed earthed metal work with non insulating material

 

[westie101]

On CNE neutral & earth are the same

On SCNE neutral and earth are the same

On PILCSTA/PILSWA the lead sheath and steel armors are both iearthed.

If working live you DO NOT want any exposed earthed bits near you when working on live cores.

 

[JohnW2]

If working live you DO NOT want any exposed earthed bits near you when working on live cores.

Quite so - which is, I presume, why stillp was implying that the shroud covering earthed metal should probably be "insulating", rather than "non-insulating"

Kind Regards, John

 

[westie101]

Ah yes, oops!
Yep insulating material

(had a lovely day restoring supply to a local hospital new build following a fire in the Energy Centre.
It wiped out
1 x 300kW CHP bio-fuelled diesel set
3 x boilers
4 x 11kV switch boards
2x transformer
1X LV board
Oh and a lot of the building and everything else in it!

http://www.bbc.co.uk/news/uk-england-cumbria-30965887
)

 

[RF Lighting]

Any idea what caused the fire?

 

[stardanny]

If there is a fault on cable buried in ground, how do you locate the fault in order to repair it, replace joint etc?

Daniel.

 

[ban-all-sheds]

Any idea what caused the fire?

A CU somewhere, I expect.

 

[OwainDIYer]

If there is a fault on cable buried in ground, how do you locate the fault in order to repair it, replace joint etc?

If it's a partial short circuit you look for the ground fizzing.

http://www.bbc.co.uk/news/uk-29214997

If it's an open circuit then a capacitance meter from each end will give you the ratio of each end to the break, or a time domain reflectometer calibrated to the cable type will send a wave along the cable and indicate the length to the break.

 

[RF Lighting]

Or by using a cable thumper

 

[westie101]

Any idea what caused the fire?

Still under investigation so I don't think it appropriate to comment on a public forum or publish the photos I've got

But
The seat of the fire was the 300kW CHP unit!

If there is a fault on cable buried in ground, how do you locate the fault in order to repair it, replace joint etc?

Bear in mind that all of our LV cables generally have services jointed to them along their length so some methods are not appropriate.

Open circuit, door knock to see who is off and who is on, this gives a start, then use a TDR to give an indication and often confirm it with a device that detects the gasses given off from the cable/ joint when it faulted

http://www.eatechnology.com/products-and-services/find-failure-causes/cablesniffer
The Sniffer can be used to confirm any fault location if used at the appropriate time.

Phase to earth TDR or fault reclosing circuit breakers with fault location capability. (often these may blow the fault clear or change it to an open circuit).
http://www.kelvatek.com/rezap.php

Phase to phase by injecting a signal between the affected phases which can be detected by a CAT. When the signal ceases thet is the fault location.

We cannot use a Thumper or such equipment owing to the connected customers as we would quickly destroy the meters and any connected equipment. We reserve that type of gear for HV

Transient faults we use equipment that can be seem on the Kelvatec website.
i.e. Bidoyngs & modular rezaps

 

[kai]

Why can't they terminate main cable into Feeder Cabinets along the street, as they do in China, and run service cables to house off that? (with correct fusing at the Feeder Cabinet.) No more live jointing required.

Another plus, is that the nonsense about unprotected 4mm street lighting feeds being run off 800amp fused street mains will be eliminated.

Maybe UK DNO's should adopt the Chinese system too!

 

[JohnW2]

Why can't they terminate main cable into Feeder Cabinets along the street, as they do in China, and run service cables to house off that? (with correct fusing at the Feeder Cabinet.) No more live jointing required.

That presumably requires an awful lot of cabinets or an awful lot of cable (or somewhere in between!)!

Kind Regards, John