I know generally it’s not allowed to put low voltage signals into the same conduit (EMT) as line power runs. But I am wondering if there are any exceptions or ways to achieve it (code compliant). For example, I know that Romex together with low voltage signals would work.

I have two applications:

  1. I need a simple RS485 connection to my EVSE. It’s mounted outside and one EMT runs to it. I do not want to run another conduit
  2. I would like to connect my Enphase Envoy (Solar) via Ethernet. It’s also mounted outside and only one thick EMT goes inside. I do not want to run another conduit

I have read that inner tubes could work. What are the exact rules for this? What inner tube must it be and how does it work with conduit fill calculations?

Or is there an exception if no low voltage signals leaves the enclosed raceway components? For example, when I would terminate the RS485 connection via an ESP32 located in a junction box and never bring a low voltage wire out?

  • 1
    maybe fiberoptic cable without a metallic jacket
    – jsotola
    Apr 24 at 7:03
  • @jsotola It's likely going to be cheaper and easier to just do it wireless instead
    – TooTea
    Apr 24 at 8:24
  • Yeah, the Envoy could be handled simply thru Ethernet media converters at each end of an el-cheapo fiber link... Apr 24 at 11:38
  • 1
    How "thick" is the EMT to the solar? Is it big enough to pull a 1/2 inch ENT tube through? That would qualify as an "inner tube" as you put it. Although it is in essence "running another conduit" but I think might be acceptable to you.
    – jay613
    Apr 24 at 17:55
  • @jay613 I think it's 1-1/4" EMT. Do you have details or reference on this? How thick must the ENT be? Could it be smaller diameter than 1/2"? How do fill calculations work with ENT?
    – divB
    Apr 24 at 19:54

4 Answers 4


Fiber-optic can go in the same conduit, Comms that is not SELV (like comms between condenser and compressor of a split system) can go in there too. some smart lightswitch comms also can go in conduit.

Comms that is SELV like CAT6 networking, loudspeaker wires, 24V thermostats, doorbells, wired intercoms, or POTS cannot go in the conduit.

RS485 to fiber converters exist and are probably the easiest way to comply with the regulatory requirements. RS485 isolators are another option allowing you to interface SELV RS485 outside the conduit with non-SELV RS485 inside it but they may raise some eyebrows.

for the ethernet, use as media conveters and run fibre. or install a wireless bridge. These things usually use a plug in power supply but hard-wired supplies are also available.

Option C run the cable on the outside of the conduit. SELV circuits don't require conduit in most applications.

  • 2
    Why is "comms between condenser and compressor" or "some smart lightswitch comms" not SELV? What is the exact feature that can make them go in there? What's the distinguishing difference to CAT6, loudspeaker, 24V tstat, doorbells etc? I am trying to understand if RS485 can be modified accordingly (e.g. with proper insulation, galvanic isolation, not bringing out wires of enclosed raceways etc).
    – divB
    Apr 24 at 21:36
  • Q2: It seems there is a way though, via tubing inside the conduit (see @jay613 comment above). But I do not understand the exact conditions (size requirements, implications on conduit fill and others)
    – divB
    Apr 24 at 21:37
  • conduit inside conduit? yeah I guess that could work.
    – Jasen
    Apr 24 at 21:44
  • 1
    @divB not SELV because engineers designed it that way, signaling relative to line voltages, (EG neutral) as it relative to neutral it's not "separated", this means installer only needs to run a single conduit for that application.
    – Jasen
    Apr 24 at 21:48

Data cables CAN be inside - but no in/out privileges.

You're installing an EV using EVEMS/Load Management, and you have a sensor module in the panel to tell the EV station the service load, so it can either prevent panel overload or capture solar you would otherwise export to the grid, etc. etc.

OK, there's what I call an "envelope" of NEC Chapter 3 wiring methods. Conduits, raceways, gutters, enclosures, junction boxes, a limited list of cable types (MC, NM, UF, SE, USE, etc.) All AC mains power wires must stay inside that envelope.

And, data cables cannot cross in and out of that envelope. This is often distorted into "data cables cannot be inside that envelope", because of course, 99% of the time people want to be outside the envelope at their router, enter "the envelope" to access an electrical conduit to the shed, then exit "the envelope" to connect to a switch at the shed. And we have to scold them not to do that. That is a network which must stay entirely outside the AC power Chapter 3 wiring method envelope.

But contrast with a case where someone has 0-10V dimming going to a bank of fluorescent lights. That entire network only connects the dimmer to the lights, so it's not hard to stay entirely within the conduits and boxes. That's fine.

Or a large campus has a bunch of conduits to carry power for HVAC equipment. They toss an Ethernet line in there for the SCADA system whose jacks are inside the AC wiring enclosures. Again that's fine because it stays entirely within Chapter 3 wiring methods.

And that's what happens with a typical EVEMS data cable.

So you're fine. Don't get psyched by that "data cables can't be inside" nonsense, that's just what we tell the IT department ;) They can be inside if they entirely stay inside and don't leave.

So if you just gotta gotta gotta go in/out, what do you do? One word. Fiber.

P.S. If you're running RS485, you're not running Ethernet. RS485 is like Spanish and Ethernet is like German. They're different languages that could run on the same telephone wire. When you say "ethernet" you probably mean "Cat 5E cable", that's the "telephone wire". That's important because Ethernet bridges e.g. to fiber aren't going to work for you, because it isn't Ethernet. No comprende.

  • You say "an ethernet" line is used in an HVAC cable conduit. What about the minimum wire size and the insulation rating in this situation? I don't know of any #18 ethernet cables. I recall you or someone else warning me, for example, not to use off-the-shelf audio cables to extend CTs, because similarly not 300V rated. Can you please clarify whether/if any data cables can share space if they remain always inside? Or are specially rated ethernet cables used in the situation you mention?
    – jay613
    Apr 26 at 13:05
  • Yes please, clarification is greatly appreciated! One additional argument for "doesn't need to be 600V rated" is that the Emporia Vue2 (power monitoring) has flimsy CT wires. But all of them stay inside the breaker panel. EDIT: Actually I just see this was subject to discussion already diy.stackexchange.com/a/214969/65210)...
    – divB
    Apr 26 at 19:01
  • One more: There seems to be industrial Ethernet cable rated for this: panduit.com/content/dam/panduit/en/products/media/7/87/887/9887/… For "Tray Cables" they say: "Designed to be installed in the same channel as cables operating at 600 V" and "Barriers are not required". Does this mean they can only be used in the conduit but STILL have to remain in the enclosure or does that mean the thick protection sleeve acts as the "inner conduit" and hence the cable DOES HAVE in/out privileges?
    – divB
    Apr 29 at 20:50
  • @divB no data cable has in/out privileges. The point of the rule is that the conduit could suffer trauma which shorted any of its wires to another, and that means you have 120V on an Ethernet wire. The cable in the conduit may withstand that, but if it goes 'out', anything could be plugged into that. Run of the mill Ethernet cable to a $20 router or a $30 ethernet card in a PC that is totally not prepared to have 120V on a data wire. Apr 30 at 19:04
  • @jay613 Just look at a home energy monitor. Minimum wire size doesn't apply to data wires. The issue at hand is what happens when AC power gets onto a data wire, now you have 277V on orange-white. The SCADA equipment will be built to at least fail non-lethally. A random Ethernet wall faceplate to a random cat5 cord to a random router to a bunch of random PCs and stuff, all bets are off. Apr 30 at 19:11

power line ethernet might do the job. This adds a modulation signal to the power line itself without requiring a separate conductor.

  • Do you mean Ethernet over power?
    – FreeMan
    Apr 24 at 16:42
  • EoP is certainly one solution without running new cable of any sort...
    – keshlam
    Apr 24 at 16:52
  • That is actually a good suggestion. The issue is that I have only found devices that directly plug into an outlet and nothing for hardwiring.
    – divB
    Apr 24 at 21:41
  • Yeah you may need to install outlets at those locations. Nema 5-15 is mechanically compatible with Fastons, but I'm fairly sure that's a cursed setup.
    – Jasen
    Apr 25 at 21:23

For the EV comms cable, since it never leaves the enclosed system, you may have some options:

  • Maybe you could use a couple of loose #14 THHN wires? Maybe not? You are supposed to use twisted pair cable but the comms speed/error requirements are probably not very taxing. If the pull isn't too far, try it.
  • if you can find twisted pair cable that is 300V rated, is at least 18 gauge, is pullable and has twistiness sufficient to meet your performance needs, that would work. This stuff exists but is expensive and specialized. It's not "ethernet" cable.
  • If that's too expensive, you could go back to the #14 and .... twist them ... it's not rocket science and you're not building a 10Gb backbone. You're in EMT so outside noise is excluded anyway, you're just eliminating the 60Hz noise.
  • So, is the reason that low voltage comms cables cannot be used that they are not 300V rated? Just curious why I would need to bother with #14 THHN? Also, does galvanic separation (transformer) help somehow? I mean, doorbell transformers are also attached to metal boxes and even supplied by line voltage
    – divB
    Apr 24 at 21:40
  • 1
    there may well be more than just 60Hz in the pipe, it depends on the load.
    – Jasen
    Apr 24 at 23:35
  • 1
    Thank you! Do you have a reference for “18 gauge or higher and insulation sufficient for highest voltage in conduit (i.e., 600V)”? Because that contradicts @Harper’s response above. He says only requirement is never enclosure and even Ethernet is fine as long as it never leaves the enclosed raceway…
    – divB
    Apr 26 at 5:24
  • 1
    Well, one of my references is Harper's answer to my own question on a similar topic. So, either you are reading too much between Harper's lines here, or I am wrong. I asked him for clarification in a comment above.
    – jay613
    Apr 26 at 13:08
  • 1
    I ran across this many times in my career as a controls electrician in commercial construction. Anyone tossing an ethernet cable (or even splicing it to 300V rated wires) in the same raceway as in that HVAC example is looking for trouble. Insulation doesn't matter, the class of the power supplies involved is what matters. Low voltage class2/3 can be in the same enclosure (if the equipment is related), but cannot be in the same raceway as power and lighting - there are no exceptions.
    – red_menace
    Apr 26 at 14:22

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