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I'm putting in a couple of new electrical lines for my back yard. I have a trench dug from point A, to B, to C, etc.. I then had a bright idea. Why don't I put speaker wires and CAT6 under ground while I have the trench open already?

The dilemma: The electrical wire is a 12/2 direct burial. It's just the wire with no conduit. My speaker wires will be in 12 Gauge, along with my CAT6, will be pulled through in a 3/4" S40 electrical conduit. This run will be about 100 ft. The big question is... will my low voltage have any interference from my electrical? Although they are running in parallel, the low voltage is in a conduit. If that doesn't work, what will be the best solution? I would hate to dig up more trench in the backyard.

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    You should also bury some underground marking tape a few inches below grade. This is so if someone digs they will find the warning tape before they find the conduit/wire. – gregmac May 21 '14 at 19:35
  • My intuition (which may be wrong, so I'd appreciate if anyone else has insight) is that just putting the low voltage in metal conduit (may need to be grounded?) may be sufficient, as it would act like shielding. – Matthew Mar 12 at 13:45
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The National Electrical Code does not list a minimum cover requirement for communications circuits, so in theory you could put the conduit at grade level. Irrigation control and landscape lighting has a minimum cover requirement of 6" (150 mm), so I'd probably go with that as a basis.

Since you're not specific about the electric power circuit, I'll discuss a few different situations.

120 volts, GFCI protected, 20 amperes of less

If this is a residential application (which I'm assuming it is, or you wouldn't ask the question), and the circuit is 120 volts or less, and the circuit is GFCI protected, and the maximum overcurrent protection is 20 amperes. The minimum cover requirement is only 12" (300 mm). In this situation, you could bury the electric power at 12", and the communication circuit at 6". This allows 6" of separation, which is likely enough to avoid interference.

Ideally you'll probably want to bury the power circuit at 18", and the communications circuit at 6". Then you'll have 12" of separation, which should be enough to prevent interference.

Over 120 volts, or not GFCI protected, or greater than 20 amperes

If the power circuit is 240 volts, or not GFCI protected, or the maximum overcurrent protection is over 20 amperes. The minimum cover requirement is 24" (600 mm). In this case, you can bury the electric power at 24", and the communication circuit at 6". Then there will be 18" of separation, which is surely enough to avoid interference.

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  • You can offset the electric to one side of the trench and the communications to the other side of the trench for more separation distance at the same depths. I'd strongly recommend two layers of "warning tape," one just below the surface, and one below the communications conduit and above the electrical wire, so it's clear that there is an electric wire as well as the communications conduit. If being picky you can get two different tapes imprinted differently and run both at the surface, but even so I suggest a second at depth about 6" above the actual electric wire. It helps when digging. – Ecnerwal May 23 '14 at 2:02
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There's no voltage safety problem. The separate conduit for the low voltage protects it and the conduits can touch.

As to electromagnetic interference, over 100 feet, and with good cat6 wire, also should not be a problem. Cat6 cable is twisted so any interference affects both wires in the opposite way, so it can be cancelled out. And go for the gold, get shielded cat6 to reduce worry even more.

Putting both conduit and wire together, with flagging tape above, reduces the chance of future damage. You don't want someone digging, finding the flagging, finding the communication conduit and then hitting the power conduit.

I'd run them together.

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