Underground ductwork - Bt and electric ducting

[revor]

I am digging a trench to put ducting in for single phase supply and also for a BT cable. This is so the current services can be rerouted when my extension is finished. I am told they can go in the same trench but I have always believed that they should be separated distance wise even though they currently come overhead from the same pole and are clipped alongside one another down the wall of the house and into the building. Does anyone have a view of how I should go about seperating these ducts or am I being too fussy given the current services are alongside one another. (By the way I have sourced my own ducting as both Scottish power and BT although promising to arrange free issue ducting have not done so.)

[Dave_L]

BT and electric can come in the same trench but obviously seperate ducts. No problems at all.

[seanandruby]

Just filled two skips so far of ducting i've dug out because it was put in wrong, it was thrown in and some had crossed over others and crushed together, sets of up to 30 ducts and more runs to come out and be reinstated. We have taken job over. I have to place them back in the correct configuation and spaced. Always lay ducts with a space between them. If you think about it a cable should lay on th bottom of a duct, that gives you a certain amount of space so allow a little more. It also helps you to get a good compaction around ducts.

[lutonlagerlout]

we find lots of ducts in the same trench all the time,leccy gas a water is very common
LLL

[revor]

Thanks for the replies, how far apart should a BT and electric duct be though. As mentioned the current supplies to the house come together but I am sure that somewhere there is a recommendation that they should be distanced to avoid emf pick up on the BT line.
Thanks

[seanandruby]

we find lots of ducts in the same trench all the time,leccy gas a water is very common
LLL

Yes i agree but they are spaced, i hope at varying depths.

[Bob_A]

Thanks for the replies, how far apart should a BT and electric duct be though. As mentioned the current supplies to the house come together but I am sure that somewhere there is a recommendation that they should be distanced to avoid emf pick up on the BT line.
Thanks

Although I don't run too many cables I'm in telecomms and have never heard of a recommendation for distance, that's not to say there isn't one but I've seen telephone cables and electrical cables fixed together with nylon cable ties over long distances and there's never been a problem.
So I'd take a guess and say it doesn't matter but 100-150mm to be on the safe side.

[Dave_L]

Not aware of any spacing between ducts, we've never done that nor have I seen anyone else do it.

[seanandruby]

Always space ducts and use adequate marker tape. i always space them myself, it's just how i was taught.

[GB_Groundworks]

not relevant but when i'm guitar teching for bands in big venues, where power and signal(guitar,vocal etc) meet always have them at 90 degress to each other so they are not running along side one another, and power cables always looped in a figure of 8 not a 0 to stop it acting like a magnet or heater and interference.

for ducting i have to say we lie them next to each other, tape at 300 above generally. really annoys me when they put tape just ontop of the ducts what good is that when cleaning through with a 13 ton machine in 50-100mm layers depending on ground conditions.



Edited By GB_Groundworks on 1257156542

[Tommy]

What bands do you tech for GB?

[Suggers]

Can't you tell ? - he's obviously a young sort of Arctic Monkey sort of bloke....
TBH - if you're building a studio, then the 90 degree thang is imperative - live gigs, they're being on the safe side - always the bleedin lighting that causes problems - funny how even in the music biz, the different trades still fight & slag each other off - just like any site....

[Bob_A]

Correct me if I'm wrong but isn't it something to do with impedance?
Things such as microphones, guitars and inputs to amplifiers are high impedance and need shielded cables, these are the sort of devices that are prone to interference.
Things such as speakers that don't normally need shielded cables are low impedance and are less prone to intereferance.

What's that got to do with ducting?
Telephone cables are not shielded, are low impedance and are not prone to interferance.

Like I say I stand to be corrected but that's the way I see it

[revor]

Thanks for all your replies looks like I was being to fussy but attention to detail is one of my good points. A strength overdone according to a friend.

[seanandruby]

Just completing a job where the ducts have to be laid in a 'tre foil' arrangement at 450 centres. will post pics when grandaughter arrives to show me how to take them off me phone onto here :laugh: