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morraphael  
#1 Posted : 13 December 2016 09:53:37(UTC)
Rank: Forum user
morraphael

Can anyone advise where I might source information on safe excavation techniques on potentail live working.

The background is: a sub contractor has found a live source 20mm from the surface on a site, encased in the cement. The DNO has been informed and the source is being investigated as it is not on any plans of the building. Aware that this does not comply to legislation, work has stopped and it is currently being investigated including CAT scans.

Thank you

Shopland23872  
#2 Posted : 13 December 2016 09:59:41(UTC)
Rank: Forum user
Shopland23872

Copy and paste this link into your browser, it will give you all the info that you need.

https://www.westernpower.co.uk/docs/Safety-and-education/Health-Safety/Public-Safety/Avoidance-of-Danger-Sept2014.aspx

Just bear in mind that an underground cable will not register on a CAT if it has no draw on it, for example a streetlight cable during the day when the lights are off. also remember that a 33KV cable will not be picked up by a CAT (amazing I know, but a CAT will not locate it)

I hope this helps

thanks 1 user thanked Shopland23872 for this useful post.
morraphael on 13/12/2016(UTC)
Blackburn31728  
#3 Posted : 13 December 2016 13:20:17(UTC)
Rank: Forum user
Blackburn31728

Only one safe way to dig when encased in concret is to isolate the service first cos that will happen when you damage it anyway

morraphael  
#4 Posted : 13 December 2016 13:25:39(UTC)
Rank: Forum user
morraphael

We're trying to determine where it has come from and where it is going. The cable melted the insulated drill bit in seconds but there has been no disruption to service and it isn't on any drawings. Fortunately the sub contractor was fine and only noticed a small flash and some smoke. I should add we're on a client site.

AD  
#5 Posted : 13 December 2016 14:43:17(UTC)
Rank: Forum user
AD

If full CAT scanning isn't picking it up (I assume a signal generator is being used with it), have you tried ground penetrating radar or is the cable sitting in a mass concrete plinth/hardstanding?

20mm is very shallow for an HVbut ought to be reasonably easy to trace (dependent on the complexity of the site and assuming some chancer hasn't just cemented up a pot ended cable). In an ideal world they'd all follow an approximately straight line into/out of the building...

I wouldn't countenance digging it up until I know what it is, where it goes and what may be around it.

You may want to refer to HSG47 iif you're not already familiar with it:

http://www.hse.gov.uk/pubns/books/hsg47.htm

thanks 1 user thanked AD for this useful post.
morraphael on 13/12/2016(UTC)
scoen  
#6 Posted : 13 December 2016 16:29:04(UTC)
Rank: Forum user
scoen

>>The cable melted the insulated drill bit in seconds but there has been no
disruption to service and it isn't on any drawings. Fortunately the sub contractor was fine and only noticed a small flash and some smoke<<

I think this is reportable as a Riddor 'Dangerous Occurance", the potential to Kill/severely injure an operative is here.

AD  
#7 Posted : 13 December 2016 17:07:57(UTC)
Rank: Forum user
AD

Originally Posted by: scoen Go to Quoted Post

I think this is reportable as a Riddor 'Dangerous Occurance", the potential to Kill/severely injure an operative is here.

No question that it could kill someone, but 'Dangerous Occurrences' are specified in Schedule 2 of RIDDOR. UG cable strikes are not directly covered, as I understand it, unless they result in 24hr shutdown or result in an explosion or fire which causes a significant risk of death.

http://www.legislation.gov.uk/uksi/2013/1471/schedule/2/made

It may well be reportable to the service provider, if its part of the main network but given the depth of the cable and the fact that it was cast into a slab it's more likely that its a 3 phase or HV cable feeding to something on site (yard lighting, external plant room etc.) which someone couldn't be bothered to run through a duct properly. Happens more than it should.

scoen  
#8 Posted : 13 December 2016 17:25:51(UTC)
Rank: Forum user
scoen

I am obviously Cut & Pasting from the HSE Riddor document, hope it's useful information though :-)

Examples of reportable incidents When should I report an electrical short-circuit or overload?

You must report an electrical short-circuit or overload (including those resulting from accidental
damage) that causes a fire or explosion and either stops the plant involved being used for more than 24 hours or could cause death. A short-circuit occurs
when there is unintended or accidental contact between conductors in a system
caused, eg by a failure of the insulation in the equipment, or a metal tool
such as a pickaxe being driven into a live cable, or a metal object being dropped onto live parts in electrical equipment.
The incident would be reportable if:it took longer than 24 hours to repair the cable

  • the explosion had the potential to cause fatal injuries

  • the cable was energised at a voltage high enough to cause electrocution, and a person holding a conducting object such as a metal tool struck it

    Please note: Contact with the energised exposed conductors of an electrical cable or circuit operating above 50 V alternating current (ac) or 125 V direct current

  • (dc) could cause death by electrocution.

  • A mechanical tool penetrating an energised electric power cable will
    create a short-circuit either between two or more of the phase conductors
    within the cable or between the outer earthed armouring of the cable and one or more of the phase conductors within the cable.

     






Edited by user 13 December 2016 17:26:55(UTC)  | Reason: typo

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