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

Steve wrote:

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

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).

--
Cheers,

John.

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Not forgetting a layer of sand underneath and above the cable to
protect it from sharp objects.

Cheers

Peter

puffernutter wrote:

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 .com,
puffernutter writes
Not forgetting a layer of sand underneath and above the cable to
protect it from sharp objects.

Cheers

Peter

Why not duct it? Always handy if you decide to add something else in the
future.
--
Bill

Bill wrote:



Not forgetting a layer of sand underneath and above the cable to
protect it from sharp objects.


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.

Peter

Why not duct it? Always handy if you decide to add something else in the
future.

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

wrote:

Bill wrote:




Not forgetting a layer of sand underneath and above the cable to
protect it from sharp objects.



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.



Its worse actually.

Peter


Why not duct it? Always handy if you decide to add something else in the
future.


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.

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...


HTH

The Natural Philosopher wrote:
wrote:
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.


Its worse actually.

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,
mused:

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?

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.
--
| Stuart @ SJW Electrical. Please Reply to group. |

wrote:

The Natural Philosopher wrote:

wrote:

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.


Its worse actually.


really? on what basis, IIRC the Pirelli site recommends moist sand on
the heat conduction basis.

And when it dries out?

What you need is wet, for heat conduction. Sand is something that varies
a lot faster than clay..

Perhaps sand doesn't have such sharp cycles
of drying out & wetting as clay??

Sharper.

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.


Aggreed.

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?

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