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.

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.

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

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

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.

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.

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.

@Texas_ranger:

Sure about PVC, not HDPE for gas??

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.

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.

I understand there's a new marker tape soon going on the market which is intended to go under the cable or conduit.

It's going to be marked with "Warning: You have just cut through an electrical cable!"

All distribution stuff here has to go in red ducting. No direct burrial anymore.

Nice one Pauluk. I've heard that the new marker tape you mentioned is available with Braille writing.Handy for when the flash has rendered the shovel-users eyes inoperative.

As for "flexible cords pulled through garden hose". That is actually a step up from "flexible cord buried direct".

I think everyones in agreeance though that only armoured or screened cables should be "buried direct". No matter what the regs say.

P.S. If the budget allows, then use conduit pipe. A buried screened cable may fail safely, but will still need to be dug up and repaired. This can be very costly and may be avoided with the use of a few bucks worth of conduit pipe duing installlation.

The problem is the wiring rules tell us that.......

Wiring systems installed underground shall be identified by an orange
marker tape complying with AS/NZS 2648.1.
The marker tape shall be
—
(a) positioned not more than 200 mm above the wiring system or any
additional mechanical protection provided;

[This message has been edited by Dapo (edited 03-11-2006).]

[This message has been edited by Dapo (edited 03-11-2006).]

It also states that a marker tape is not needed for orange conduit. I can't understand why they decided that. It appears they only considered someone manually digging it up rather than by mechanical means.

There is a proposal for the next edition that marker tape is always installed and placed at approx half the depth of cover.

Sometimes it doesn't matter what markers and warnings are provided.

Back when I was at the BT satellite station, there was one time when they had outside contractors in to dig foundations and other trench work for one of the new dishes and associated buildings.

One of the diggers was stopped just in time to avoid his shovel going through one of the site's 11kV distribution cables (fortunately one that wasn't energized at the time, but he wasn't to know that).

When hauled in front of the manager and asked why he didn't stop when he hit the huge marker tape with "DANGER High-voltage cable below" emblazoned in gigantic letters along it, his reply was, apparently:

"Oh, yes, I saw that. I didn't think it was important."

No, not really. About the only thing I know about it is it's yellow plastic.
Supposedly a gas company employee one said that after ten years under a busy street that kind of pipe is as flat as a pizza... still they keep installing it. Our gas mains leaked in five spots on a distance of 15m...

From RODALCO:




A lot of new cables now these days go in pre drilled heavy duty conduit.
These will have no warning strip above it, If a digger scrapes the ground it will possibly not break the conduit and therefore not damage the cable.
These methods are used extensively in Auckland now in OHUG programmes and for 11 and 33 kV feeder upgrades.
These feeders are laid in the middle of the road and manholes provided for termination joining pits.

Some of the protective strips I've seen here actually go together like a jigsaw. I _think_ they were from the cable company, but they might have been phone too (the phone lines were laid in 1992 when I was 7, and the cable not much later).

Gray(Dapo),
That rule about the depth of the signal strip is about the only electrical regulation that I've ever thumbed my nose at.
If I'm burying a cable or some conduit, the strip goes at half the depth of the trench, no questions.
One other thing, ever noticed how when a digger bucket catches a signal strip, it stretches the plastic (as it is supposed to do) and ends up pulling a significant length of it out of the dirt, before it snaps.
I often wonder how many people actually bother to replace the bit that's been pulled out of the ground, further along the trench from where they are digging?.
Makes the next dig in that area fun with no strip in the ground.

{Edit: BTW watch the edges on that MagSlab stuff, they are bloody sharp, one guy at work managed to cut open a cowhide glove he was wearing while installing some.
I'd hate to think what would have resulted if he hadn't been wearing work gloves!}

[This message has been edited by Trumpy (edited 03-25-2006).]