Should I dig a separate trench for CAT5e wire to shed?

Question

I am renovating a shed which is going to require doing at least a 100' trench for power from the house. I also want internet via a hard wire out to a a WAP in the shed. My question:

To avoid EM interference, do I need to run a separate trench just for the network cable?

My intuition tells me dropping even a shielded cable in with the 60-100A power line will not end well. Maybe a wireless approach would be more cost effective?

Updated 10/13: thanks for all this great information...let me clarify the use case here. The shed/cottage is to be for peloton, yoga, tv; like a "she shed," but it's for "us" :) I walked off the likely path to get conduit from router in the basement to the shed and it is more like 200 feet. So I am thinking this is like $50 of cat5e stuff, $200 for fiber, or there are these long range wifi things I have seen on amazon that look like $150-200 or so. I would not want to spend much more than that.

Answer 1

Same trench is fine. Use conduit, you may want to upgrade it later without re-trenching. Keep some space between the conduits, vertically, horizontally, or both.

Interference between 60 Hz power and 100+MHz ethernet is wildly overestimated by numerous people. Ethernet encoding is designed to ignore noise, and ethernet cabling is deign to reject noise so it does not get picked up, and the "noise" of a powerline is very, very much slower than what goes on in ethernet.

Still, the better bet for "what goes in your conduit" is fiber optics, but that's mostly because it provides total electrical isolation for your network equipment at both ends. It also happens to be immune to any electrical noise along the way, but that's far less likely to be a practical problem than you imagine, while side effects of thunderstorms are far more likely to be a practical problem with a wired connection.

Whatever cable you place should be "wet-rated" - for whatever reason, direct burial cable seems to be the most common wet-rated variant seen in ethernet, but put it in a conduit anyway. Outdoor conduits are defined as (and usually are) wet locations.

Answer 2

Definitely go conduit here

I would lay two conduits (one for mains, one for data/telecom) if I were in your shoes; this way, you don't have to dig anything up later to upgrade it. 1" is adequate for most telecom cables you'd want to run; however, while a second 1" will accommodate smaller mains feeders (up to 60A, or perhaps a bit more), I would recommend using 1.5" instead if you are interested in having a full panel at the shed with a feeder to it instead of a simple MWBC+disconnect box configuration. That way, you will have enough room in the future for a 100A or 125A feeder that's ample for a full-blown shop, ADU, or other such power-hungry use in the future. Don't forget to leave pull-strings in conduits you aren't going to use right away!

Fiber is also a very good idea, because you'll need some primary protection otherwise

The other thing you'll want to do is get a couple of small switches with SFP support (or media converters, if you can't find suitable switches), a pair of SFP transceivers with duplex LC connectors on them and some preterminated direct bury/wet location duplex fiber patch cord (LC/LC) of the appropriate length for your run (don't forget to leave length for the stub-ups at each end!); this way, you won't have to deal with the problems inherent with running copper telecoms lines outside. If you do insist on using copper for this application, you'll need to fit UL497 listed primary protectors at both ends of the run to satisfy 2017 NEC 800.90(A) regarding interbuilding circuits that are exposed to lightning, as that's the main threat to your Ethernet run, not mains interference.

This requirement, unfortunately, is not easy to find parts for when it comes to datacom circuits. ITW/Linx is the only vendor I've been able to find carrying any (no affiliation with them), and their CAT6-75-110 model would be the best suited for your application I reckon. You'll need one for each end of the link in order to protect both buildings from lightning or power cross induced voltages. Furthermore, you'll need to connect their grounding points to the intersystem building termination or grounding electrode system for their respective buildings with a 10AWG minimum bare copper ground wire in order to meet installation and NEC bonding requirements. This also means the shed will need to have a grounding electrode system (2 8' rods 8' apart, connected to the disconnect or subpanel with 8AWG minimum bare copper), even if it is not otherwise required to have one by Code.

Answer 3

Once you've done all the hard work of digging the trench, dropping an oversized conduit for the power is a cheap upgrade, as is dropping a separate conduit for the low-voltage wiring. Conduit, while it will cost a bit more to install, is very cheap insurance against any future upgrades/repairs, as it's pretty dead simple to pull replacement wire/cable through the conduit as opposed to re-trenching to direct bury new cable.

Whether it's required or not, there's not much reason not to, and it certainly won't hurt. Though, I'm not sure that PVC conduit will do much to stop the EM, the construction of both the mains voltage and low-voltage cabling will do a fair bit to reduce/eliminate the interference.

Just be sure to use CATx cabling appropriately rated for outdoor/wet area use. As I've been reliably informed, buried conduit will fill with water. It's guaranteed enough that you should just go ahead and fill it immediately upon installation to get it over with... ;)

Answer 4

I don't think you'll have EMI problems with your CAT5e because of the voltage-diffential-signaling nature of modern Ethernet. Any induced current from the electrical feeder to the CAT5 should not cause problems.

However, you may want to use a conduit instead of a direct-burial CAT5 cable. For 100' the conduit will be inexpensive and allow you to replace the CAT5 with optical fiber or other types of data cabling in the future, if desired. If it were my project I'd consider conduit for the electrical feeder as well; same reasoning, plus in some areas, your trench can be shallower, depending on if you use metal or PVC conduit.

Answer 5

Ethernet is supposed to be EM tolerant, but if it's really a concern, there are other options. Running a second line through another ditch is asking for maintenance problems down the road.

Option 1 Run your power line in shielded cable or conduit. Then your Ethernet line can lay in close proximity without worry of EM interferrence. Note: If using shielded cable, make sure the shielding is properly grounded on one end.

Option 2 Use the newly existing power line to do Ethernet Over Power (EOP), not to be confused with Power Over Ethernet (POE).

Ethernet Over Power (EOP) converter example

Option 3 Run fiber between your buildings. Fiber optical cable is completely impervious to EM, as well as the deleterious effects of ground water.

Ethernet-Fiber converter example