Hi I am about to fit a gate automation system and need to run a supply cable ie: 3 core armoured with an additional 5 core intercom cable. What depth do i need to lay the cable at and what additional precautions are require to comply with building regulations
Can anyone help Regards Steve
There are no absolute requirements for cable depth, you should use what is sensible for the situation.
450mm is the normal suggested minimum depth, however you may need to increase this is areas that are likely to be deeply "dug over" (flower beds etc).After you bury the cable you should backfill the first 150mm or so and then bury a "cable below" warning tape (usually yellow plastic stuff - you get it on long reels from electrical wholesalers etc) before filling the trench. That way anyone in danger of digging to far will get to the tape first.
It might also be wise to ensure that there are at least a couple of inches of separation between power and signal cables along the full length of the run (to eliminate mains hum on the signal circuits).
Not forgetting a layer of sand underneath and above the cable to protect it from sharp objects.
Cheers
Peter
Don't be daft. You simply don't bury te sharp objects in the same trench.
Bury them somewhere else.
In message , puffernutter writes
Why not duct it? Always handy if you decide to add something else in the future.
SFAIUI the main purpose of the sand is to help conduct heat away from the cable on the basis that damp sand is a better heat conductor than clay or rock.
I posted a query here about this a year or so ago: concensus was that underground ducting has gone out of fashion. Two factors came out - modern armooured cable was designed to be suitable for direct burial, plus ducting collects standing water. Would also speculate that heat conduction might be less in a duct, thus effectively derating the cable (though that isn't going to matter for a gate opener).
There was a little info about this on the Pirelli website (look for cable specs) or google this newsgroup looking for Pirelli.
HTH
Its worse actually.
Indeed. I scraped the armour on my incoming (coaxial) mains when trenching it in..wrapped it in PVC and left it.
Fuse started banging later on...but I felt chuffed when they found the cable had been buggered not by me, but by the digger driver who dug the new foundations. 6 years on and its fine..
We are on clay, and simply backfilling and laying the warning tape over it was all that was needed. They undergrounded my overhead 11KV and that did not get laid on a bed of sand either...just in wet sticky clay.
Its been subjected to being under a buuilding site with 30 ton trucks regularly going over the top of it - its about 500mm deep - no worries.
The trench has settled in the years a bit..so the wet clay has obviously settled aroudnd it.
BT run underground ducts, and they have fixed my line, or a trunk feeding it, about twice a year the last 10 years...
really? on what basis, IIRC the Pirelli site recommends moist sand on the heat conduction basis. Perhaps sand doesn't have such sharp cycles of drying out & wetting as clay?? Also that it should be at least 450 deep to give a good chance of being in a moderately constant temperature & dampness zone - not just to avoid spade damage.
On a different tack, the OP mentioned that a signal cable is required to run with the SWA. I'm far more wary of burying this unprotected, but don't know what the correct or recommended method is. Anyone know? (to OP:) What tyep of signal cable is to be used?
On or around 2 Nov 2005 14:34:52 -0800, jim_in snipped-for-privacy@hotmail.com mused:
I wondered when someone would remember about that! I'd tube the signal cable or use direct burial type. Usually any telephone\alarm cable will do the job.
And when it dries out?
What you need is wet, for heat conduction. Sand is something that varies a lot faster than clay..
Sharper.
Also that it should be at least 450
Aggreed.
I'd be tempted to put that in some kind of flexible plastic trunking, and gob silicone into each end of it.
Won't be spade proof so go deep.
Frined of mine used a bit of plastic plumbing p[ipe - the siort used in UF heating. Ive seen other people use what looks like standard basin waste pipe. There I might uses sand to spread the backfill load a bit - easy to crack that stuff.
Hi Thank you for your helpful advice. regards Steve
Hi John Again many thanks for the info, this has been of great help regards Steve
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