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#145055 - 03/03/06 04:59 AM Direct Burial vs Conduit?
Trumpy Offline

Member

Registered: 07/05/02
Posts: 8540
Loc: SI,New Zealand
Folks,
I'd like your opinions on this method of burying cables.
Over here in New Zealand, you are allowed to direct bury Neutral-Screened cable, provided it has an Outer sheath of 3.2mm thickness and it is buried in "fine sand".
This means no de-rating and no further protection.
Once covered over the cable is "there", stuck there as it is.
I was always bought up with this method of laying cables, as an EC.
But one thing the other day made me think otherwise.
Drawing wires or cables has got easier since we used Conduit wires in PVC conduits and we have lubes to help us.
What is your preferred method?.
We have up to 200mm dia conduit and if you can't get a cable through that you've got problems.
It also makes replacement or drawing in new wiring easier.
Take your pick.
_________________________
Let's face it, these days if you're not young, you're old - Red Green grin

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#145056 - 03/03/06 07:26 AM Re: Direct Burial vs Conduit?
renosteinke Offline
Cat Servant
Member

Registered: 01/22/05
Posts: 5305
Loc: Blue Collar Country
Apart from the issue of protection, I like pipe for two reasons: Changes and cheaters!

Pipe allows you to later upgrade the system by pulling new wire. Since I hate digging, using pipe meand never having to dig again.

We have rules, as well, regarding depth of burial and the use of "clean fill." In my experience, however, the folks who use direct-burial cable rarely place the cable more than a few inches deep, and are quite likely to lay rocks right atop the cable!

So, from my point of view, I've come to associate direct burial cable with lousy installations.

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#145057 - 03/03/06 03:30 PM Re: Direct Burial vs Conduit?
Alan Belson Offline
Member

Registered: 03/23/05
Posts: 1801
Loc: Mayenne N. France
Mike, don't you have to put some sort of 'marker' tape over the buried cable to warn future diggers? [ no offense, Aussies! ]
Agreed Reno, the bodge artistes are never short of crackpot ideas, like the pillock in Bath, England, who decided to dig a cellar under his stone-built house. The whole structure fell into the massive hole and killed him. On one memorable occasion in a house renovation, I found under a damp patch in the plaster, a partly-burned log, obviously straight out of the fireplace, set neatly in mortar in an inside wall at sill height. The 'DIY' previous owner must have run out of bricks and improvised! We had visions of him laying it with firetongs to avoid burning himself!

Alan
_________________________
Wood work but can't!

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#145058 - 03/04/06 05:38 AM Re: Direct Burial vs Conduit?
pauluk Offline
Member

Registered: 08/11/01
Posts: 7693
Loc: Norfolk, England
I don't know about the heavy industrial side of things, but for lighter duty such as domestic and small commercial, I'd say that direct-burial SWA is far-and-away the most common method here (not counting homeowner specials such as flexible cords pulled through garden hose, etc. ).

Most of you already know what SWA looks like, but just in case:



It's widely available in 2-, 3- and 4-core variants with conductor sizes from 1.5 sq mm upward.
http://www.tlc-direct.co.uk/Main_Index/Cable_Index/Armoured_SWA/index.html

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#145059 - 03/04/06 05:48 AM Re: Direct Burial vs Conduit?
briselec Offline
Member

Registered: 12/28/05
Posts: 141
Loc: Brisbane, Australia
About 3 years ago we upgraded a shopping centre and installed parallel 240mm² cables for the mains. 70 metres of the run was in a garden bed between the trees and the kerb with 3 detours around drains. Just the thought of how much work it would take to do in conduit made me decide to bury it direct.

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#145060 - 03/04/06 11:46 AM Re: Direct Burial vs Conduit?
Wolfgang Offline
Member

Registered: 09/25/05
Posts: 154
Loc: the very West of Germany
In Germany you bury cables usually directly, minimum 0.3m without or 0.6m with traffic . Cooling is better than in a conduit, so you can uprate them and refer to 15°C external temperature. Furthermore, also in a conduit you will have to use the same cable, as there are no ground water(is often a bit acid) resistant wires. Buried conduits are not regarded as water tight except short distances (< 10m from cellar to cellar) where the conduit is well accessible and has a defined slope.

There are cable types with concentric (PE connected) shield, which are rarely used, as more expensive. Normal unshielded earth type cables (called NYY) are not regarded as dangerous.

And as already mentioned in other threads in German towns usually everything arrives underground and without conduits: phone, cable tv, electricity, gas and water. You are supposed to lay either a coloured information tape or special plastic protection or bricks above the cables.

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#145061 - 03/05/06 01:45 PM Re: Direct Burial vs Conduit?
Texas_Ranger Offline
Member

Registered: 12/17/01
Posts: 2343
Loc: Vienna, Austria
Utilities usually bury directly here. Cable, then sand, then bricks, then marker tape or 4mm(?) sheet plastic (yellow, with warnings printed on), then more sand and finally gravel or soil. Seen it quite often during the last few years... in 1991 we got all new phone lines in the street, a few years after cable TV (fiber optical) was installed, then we got a new power feeder... and last year when they replaced the gas mains some cable protection showed too. In case of the PVC gas lines they even poured concrete atop of the pipes, down in the trench and then backfilled with soil.

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#145062 - 03/05/06 02:02 PM Re: Direct Burial vs Conduit?
Wolfgang Offline
Member

Registered: 09/25/05
Posts: 154
Loc: the very West of Germany
@Texas_ranger:

Sure about PVC, not HDPE for gas??

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#145063 - 03/06/06 12:31 AM Re: Direct Burial vs Conduit?
Trumpy Offline

Member

Registered: 07/05/02
Posts: 8540
Loc: SI,New Zealand
Alan,
Yes, you are required to provide a "Signal Strip" at half trench depth.
But with the types of excavator operators we have here these days, they are either colour-blind or couldn't give a toss.
Umm Dirt Brown- Signal Strip Orange, must mean keep digging.
One thing I will say though.
That SWA cable would last 5 minutes here under some of our digger operators.
We tried to train a few of them to the PoCo way of thinking, 2 came out as good operators.
1 died since from a heart attack.
Geoff is our man.
Working an excavator is something that takes real skill, I'm a kid as far as that is concerned.
_________________________
Let's face it, these days if you're not young, you're old - Red Green grin

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#145064 - 03/06/06 03:42 AM Re: Direct Burial vs Conduit?
briselec Offline
Member

Registered: 12/28/05
Posts: 141
Loc: Brisbane, Australia
 Quote:
Mike, don't you have to put some sort of 'marker' tape over the buried cable to warn future diggers? [ no offense, Aussies! ]

Here in OZ when cable is buried direct you have to install a thick protective strip. It's not a code requirement to install a marker tape for underground conduit but it's often done anyway. It's amazing how often you find it sitting on top of the conduit which makes the exercise pointless.

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