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I am going to run an underground 50 amp circuit to my detached garage for an EV charger. The distance from the house electric panel and the garage is about 60 feet. I was planning on putting the power lines (4 or 6 AWG) in conduit. It would be nice to run a data cable to the garage at the same time. Can I put CAT-6 ethernet cable in the same conduit? Or better in a separate conduit in the same trench?

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The only practical way you can run data through a power conduit is if you use fiber optic (no metal) and handle the details "just right". While that makes sense in some situations, 60' is well within normal ethernet range, and the usual solution is to run a separate conduit for data, which can contain any low voltage wires you need - e.g., Ethernet, phone, coax (cable TV), etc.

I don't recommend WiFi for this use. Even for one device, hardwired Ethernet will be more reliable. And even if you only need one device, I'd put in a switch on the end of the Ethernet. Which is kind of like a subpanel for data...

Unasked related questions, but I'll answer them anyway:

  • Wire size/type:

Instead of 4 AWG or 6 AWG copper, consider 2 AWG aluminum. It is far cheaper and can handle up to 90A. The only catch is if your local jurisdiction won't allow it (like mine). However, there is normally no limitation if it is a feeder to a subpanel instead of an individual circuit. And since you are in a detached garage:

  • Detached Building Stuff:

    • Disconnect needed. But that can be the main breaker of a subpanel
    • Ground rod needed (likely 2)
    • Subpanel is a very good idea. Not only does it pretty much guarantee that aluminum feeder will work well, it will allow you to add additional circuits as needed, up to the total feeder capacity (e.g., 90A for 2 AWG aluminum). That can be for a 2nd EV, lighting, tools, heater, etc. A subpanel doesn't have to be small - a large "main panel" is OK, and pricing is often crazy enough that a big main panel with a few "free" breakers will cost around the same as a small subpanel.
  • GFCI - Almost certainly required for all 120V receptacles and possibly for other stuff. 240V GFCI means GFCI/breaker. 120V GFCI can be GFCI/breaker or GFCI/receptacle.

In the case of your EV charging, if you are on NEC 2020 it may be required for that as well if you use a plug/receptacle connection. Hardwire and you avoid that problem.

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    Downvoter care to explain what I got wrong? Commented Nov 2, 2022 at 4:52
  • Not them (I upvoted to reverse) but you really want fiber here, unless you are going to spend generally more than fiber on properly protecting the cat6/5e/6a/7 copper wiring that runs outside. Yeah, sure, "everybody does it without that" and "everybody" is not up to code.
    – Ecnerwal
    Commented Nov 2, 2022 at 14:12
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    @Ecnerwal But if you actually run a separate conduit (which OP indicated they can do) then it isn't a problem. Just sticking a Cat 6 in the ground - and I've seen people do that - is not a good idea. Commented Nov 2, 2022 at 14:36
  • I've read that fiber is better between buildings because of voltage differentials during a lightning strike can kill the Ethernet devices. Fiber isn't affected by lightning. Commented Nov 2, 2022 at 21:02
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    The "between buildings" aspect brings in a requirement for "primary protection", under atricle 800, which copper cables need and fiber cables sidestep. "In addition, where there exists a lightning exposure, each interbuilding circuit on a premises shall be protected by a listed primary protector at each end of the interbuilding circuit." There's some more info about exceptions, but they probably don't apply.
    – Ecnerwal
    Commented Nov 2, 2022 at 21:06
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I'm going to pull you in 2 different directions at once.

EV charging size - don't go overboard

If cost is no object, why not? Because your house's service may not be able to handle it. I know you've got a notion there, but the only thing that counts is the NEC Article 220 Load Calculation, which already has all valid notions professionally applied to it using data-driven science. Since EV charging applies 100% to the Load Calculation, you can simply run the Load Calculation on the house as it is now, and compare to the ampacity of the electric service.

Other than that... the error we see is people thinking they need to put in some huge charger when really, nobody needs to charge 350 miles in 10 hours. Especially with DC fast charging being ever more available. Technology Connections covers this point wonderfully here.

A subpanel is mandatory here... or awkward disconnects.

You already have electric power to the garage, and you're not allowed to have 2 separate supplies to an outbuilding (NEC 225.30). (Except under very special conditions, and then the disconnect switches have to be grouped (NEC 230.71) and have to be where power enters the building -- and doing that is a royal pain.)

So the only way you can make this work without a subpanel is if the original line is 120V, the EV line is 240V, the EV line enters the garage right next to the original line, and disconnect switches are added to both right next to each other (and they can be indoors).

The added complexity of all this is not worth it just to avoid a subpanel. Subpanels are cheap. Feed existing circuits off the new subpanel, and abandon any existing circuits from the house. (they can be reused for "switch loops" to control lighting from the house, but the power on them must originate from the garage). The only annoyance is the outbuilding now needs ground rods but it probably needed them before.

"Oh no, this means even bigger wire. I'm not made of money here!"

Feeder size - do go overboard!

Because of money. You will need a subpanel or disconnect here, and those things have lugs that are made of aluminum. (aluminum lugs play well with both copper and aluminum wire). Further, LARGE aluminum wire has a rock solid safety record that is undisputed. This has a bizarre effect on the economics of heavy feeders.

90A feeder (#2 aluminum) is actually cheaper than 40A #8 copper feeder and about the price of 30A #10. And even the most superstitious authorities agree #2 is perfectly safe. #2 is at a pricing sweet spot due to its widespread use for service wire, so #4 is not economical and #6 is barely cheaper.

The problems in the 70s with small branch circuits were largely UL's fault for hastily and improperly certifying 15 amp sockets for use with aluminum, and nobody using torque drivers on the small stuff back then. Not a problem for an AL lug torqued to spec.

Other circuits in the conduit

First, other power circuits are not allowed due to the "1 circuit per outbuilding" rule. (lamp switch loops are allowed but would result in a "thermal derate" of #2 aluminum down to 80A because the lamp circuit has to cool too.)

As far as data, no go. Cannot ever mix data and power in the same enclosures, conduits or raceways. A wire problem could cross mains voltage onto the Ethernet wires, and cause all manner of shock and fire.

However, fiber is allowed if it does not have any metallic parts. For obvious reasons.

Second EV

Modern technolgy (called "Share2" or other names) inside the EVSE charging gateway allows two or more EVs to dynamically split a single power allocation. The master EVSE is told "you guys share 40A" and they talk to make sure no amp goes unused. Most of the time only 1 car is actually charging, and it gets all of it. For instance a family with three EVs could make do with a 50A circuit - if one car needs extra charge, just use the EV console to delay charging on the other two. The one will get the works.

However, NEC has not been updated to accommodate Share2, and they still require a dedicated circuit per EVSE. So you need a subpanel, even though the sum of EV loads does not add up to more current than 1 of the circuits.

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    Would you go conduit with conductors or teck cable? If you go teck cable you could also just run a small conduit in the same trench for the low volt stuff instead of having two conduits. Commented Nov 2, 2022 at 22:01
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Cat6 in its own conduit, Fiber in the same conduit. But ..either way for the money and effort I'd spend it instead on an upgraded Wifi mesh including outdoor units for the house and garage. You'll get coverage in your yard and driveway for free as part of that effort and if you haven't done that kind of work you'll learn some new skills.

Or the cheap, ugly easy way: a couple of bamboo masts with Cat6 strung between them. Plenty of things wrong with that but It'll work for a few years and then you can replace it for $20.

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You can put it in the same conduit, but if you do you will not be allowed able to use it for ethernet or telephone or any other SELV application.

you can put non-conductive able like fibre-optic in a power conduit or you can put a second conduit in the same trench and put your data (and any other SELV) in that,

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