Low Voltage underground conduit separation from 120V

I'll be running some underground PVC 1 1/4" conduit a distance of ~200' for low voltage wiring such as Cat 6 and Coax.  Also there will be a separate underground PVC conduit containing one or more electrical runs for some lighting, plugs, fans and circuits to an outdoor kitchen, all 120V.  There will not be 220V, just 120V.   I'd like to do just one trench to contain a 3" ABS drain, the low voltage conduit and the higher voltage conduit. I'm concerned about distance of separation between the low voltage conduit and the higher voltage conduit, and the possibility of inducing AC onto the data wiring.  Does anyone have any reference material I can look at for guidance?


Senior Member
There may be local rules in the building code about required separation.  Here I ran 230V, gas, and low voltage about 200' to a detached garage.  Local AHJ (Authority having jurisdiction) said gas needed to be 2' from power and didn't care about low voltage.  Still I wanted some separation.  So the trench was dug with a 2' bucket and the power and ground placed on opposite sides (technically ended up with an inch or two less separation than 2').  Low voltage was placed in the middle.  I like to have at least 12" but with the twists in low voltage noise pickup may not be much of an issue.  Sounds like you will be trenching this in so you will have a much narrower trench.  Use bigger conduit than you think you need - makes it much easier to pull in bigger wire later if you want.  Don't have any specific references but have generally seen the recommendation of at least a foot separation when running any distance in parallel and to cross power wires at 90 degrees or close to it if possible.  I have a few feet here and there in the house where they run parallel and haven't had any issues.


Senior Member
If you place the conduits on opposite sides of the trench, you should be fine.  The twisted pairs in CatX cable provide a decent level of immunity from noise.
A bigger concern would be what are you going to do about protecting the data cable and attached equipment from surges.  Outdoor wiring is a great path for surges from nearby lightning strikes to enter and cause damage.   Rather than running CatX  cable, run fiber instead. 


Senior Member
I'll second the fiber recommendation.  Takes electrical protection right out of the equation.  It's pretty easy and cheap these days to get fiber to whatever adapters.


Senior Member
Surge protection is an issue with wire.  At a minimum you should put surge protection at both ends.

Mark S.

Active Member
I have about 1 foot separation between 240V and several runs of low voltage (Cat 5e, RG6U, alarm) - not nearly 200 feet - but have not had a problem in 20 years - except for one problem.   I ran out of room to pull more wire.   As JimS recommended, lay down a much bigger conduit than you think you need, and leave a heavy duty pull string in there when you're done - you will probably use it.  I have no experience with fiber, but seems to add complication, unless you have serious lightning issues in your area.


Active Member
A reminder.
The OP mentions using  a 12/2 with ground wire in underground conduit. IIRC, that would violate the NEC if the 12/2  is type NM (Romex) and not UF cable. Underground conduit is considered to be a wet location by the NEC and all wire in it , ethernet cable included, needs to be rated for wet locations. NM cable isn't so rated.
Just say'n


While you have the trench open, drop an extra conduit, and maybe an irrigation/water pipe, very inexpensive.
I won't be running the 120V wiring, just the low voltage wiring.  The 12/2 w ground is just my way of saying it's not #10's for 220V, 12/2 w ground is not actually what the electrician is running, and  I edited my original post for clarification.  He is running  the electrical wiring in whatever water resistant, underground cable he chooses.  We're trying to find out how wide of a trench we need to dig in order to keep the low voltage far enough away from the 120V so there won't be any data disruption caused by the 120V.   So far, it sounds like the separation doesn't have to be much because the electrical will not be 220V and there will be separation by means of individual conduits.  


Senior Member
It's not just lightning. Any conductor that is connected to ground at both ends will share any fault currents from devices that fault to ground. If a saw in your outbuilding faulted to ground and it raised the ground levels to say 60 volts between ground locations, for 1/10th of a second, until the breaker pops, your data cable ground and likely signal lines will have to carry that 60 volts also, from end to end of the cable. Electronics don't like that.