phone and power lines in the same trench

This is something that is done regularly, provided the right steps are taken. There are minimum distances for Joint Trench applications, but I can't think of what they are right off hand. In the current project that we are working on, our telecom conduits are concrete encased and they must be a minimum of 3" from the electrical. I think its somewhere around 12" when they're not concrete encased. Hope that helps for a starter.

JT

(snip regarding multiple conduits in one trench)

Note that any such requirements are safety requirements.

Metal conduit should easily be enough to shield signal cables from power cables.

I would expect properly configured ethernet to work even in the same conduit, though it likely wouldn't satisfy code.

Analog voice lines are more likely to be affected by coupled interference from power lines than network cabling would be.

-- glen

Given the vastly different frequencies involved, there's not much rick of interference.

None of our OSP conduits are metal. Everything is schedule 40 PVC. And yes, the distances and concrete are all safety related, having nothing to do with performance.

There are two issues. One is the safety aspect, and that's regulated by your codes. But chances are, there is some acceptable vertical separation. Bury power {say} 1 m. down, backfill to 0.5m, bury duct, backfill rest.

Interference is less of an issue; after all, the telco cable runs parallel to power cabling for MILES to get to your house.

That said, you should not be burying comm cable. Once the power is in and backfilled over; then bury at least two plastic ducts, & pull cable through later.

The best duct is the special 1" or larger heavy wall plastic pipe with a ridged interior surface. Not sure Mitre stocks it; See your local bankrupt fiber company...

Failing that, get polythene water pipe with the heaviest wall thickness.

(Even if your land is 500KM west of the Alice and last saw rain during WWI; I'd not bury metallic conduit, as its lifetime will be quite limited.)

Depending on the length of the run, you'll want to put in intermediate pull boxes.

Just make sure that the two conduits are separated as far apart as practical, no less than 6" but preferably more, and _stay_ separatted when the trench is filled in. Something like bricks could be used for spacers every few feet, or other hard material. Then make sure the AC line is twisted, too. Your phone line feed should already be using twisted pair. And properly ground your electrical system at the house.

Thanks everyone for your responses

-Adrian

Network cables I wouldn't worry at all about. Voice cables might pick up a noticeable amount of signal if they are too close, and there is a lot of noise on the power cables.

-- glen