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Posted By David Brede
I am advising a demo contractor regarding working on breaking out a concrete slab under which is a HV cable. I have clear information about the location of the cable
Clearly this has to be isolated and cut off before the slab is fully removed however what is the guidance on a safe distance that the slab could be broken out in advance of this?
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Posted By rks
I would suggest that you have a look at HSG 47 and the HAUC manual concerning working near and around underground apparatus and working on the highway and in foot ways.
Regards
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Posted By Robert.
The issue primarily is the HV cable and one of avoidance.
Yes, HSG47 gives guidance.
Can you be absolutely sure that there are no other conductors there?
If youre using a CAT, remember it will tell you that something's there but not that nothing's there.
Isolate the supply---------highly inlikely if it serves commerce and public.
Ask the supply authority to assist as some HV cables are very sensitive to "shift" and movement.
Get a full proper utility trace done and find depth. I'm assuming that it's not on public path etc etc otherwise the street works act comes into play
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Posted By Mike Miller
preferaby 1m either side from known service consider hand digging trial pits before using any excavator or pecker/breaker tool
Mike
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Posted By Andy M
It would also depend on the depth between the underside of the slab and the crown of the buried cable. Is the cable considered "Fragile"? Some older electric cables were oil filled and would not take much vibration to cause damage. I would consider cutting the concrete slab with a floor saw and remove a 1 metre strip of the concrete floor, directly over the line of the cable, by lifting sections out with a machine.
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Posted By Granville Jenkins
I would suggest that there is no safe depth, as you cannot guarantee at what depth the cable will be located, for example, I had a project where a live 415Volt cable was found directly under a back inlet gulley, the cable was less than 12inches (300mm) below ground level.
Regards
Granville
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Posted By RP
You should not break out the concrete without first isolating the electric cable. Please contact the cable owners for their help with this.
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Posted By Dan dan
I have had Teams who have undermined and come across two 33 kv cables under the concrete slab with the 11 KV cable encased within a duct in the concrete itself (whats taht all about) .
General concenus - it is enmcased in concrete to assist protection and prevent damage
Call the leccy board and arrange a site meeting (follow up in writing. Discuss options with them. I hve done this on numerous occasions and we have come to a logical agreement - sometimes not i.e non commital" its a case of doing all that is reasonably practicable. If you go ahead and you havent been in touch with the plant owners and something does happen that is their first cop out - been there done it
The rule of thumb is get isolated if poss and dont break out as 9 times out of 10 you will cause damage and or serious injury - that ducting is brittle - if it is in ducting
use GPR or an RD4000 CAT with its Generator to establish approx depth (hire one for the day)
In some cases if the plant is in ducts which it should be but not always - guys in the past have used hand nibblers to expose. Risk assess and provide method statement even go so far as permitry. What ever you do contact the leccy board
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