Cat 5/6 in same conduit as power: is NM-B required, or is THHN acceptable?

Question

Preface: I'd like to avoid the question of whether one should run data and power together; my question is focused on Code compliance.

I'm trying to ensure I interpret Code correctly when running Cat 5/6 cabling and power together in the same conduit. For starters, I understand that nothing in Code prohibits one from doing this; I'm trying to ensure I understand how to do it properly.

I'm wiring a basement office for power and data, and I'll be running the electrical in EMT. My plan was to pull THHN for the power rather than pull NM-B, but then 800.133(2) Exception 1 made me scratch my head. Is my understanding of the Article that if I want to run both data (Cat6) and power in the same conduit, that the power needs to be sheathed (i.e. NM-B). Is it unacceptable to pull individual THHN conductors and the Cat6 together in the same conduit?

800.133 2) Other Applications. Communications wires and cables shall be separated at least 50 mm (2 in.) from conductors of any electric light, power, Class 1, non–power-limited fire alarm, or medium-power network-powered broadband communications circuits.

Exception No. 1: Where either (1) all of the conductors of the electric light, power, Class 1, non–power-limited fire alarm, and medium-power network-powered broadband communications circuits are in a raceway or in metal-sheathed, metal-clad, nonmetallic-sheathed, Type AC, or Type UF cables, or (2) all of the conductors of communications circuits are encased in raceway.

Answer 1

You mean 800.133. And this very concept of mixing comms and power is highly improbable. I know you're casting around for a way to do this, but this sort of "hopeful reading" is very highly prone to confirmation bias.

NM-B is always useless in conduit

Using NM-B in the conduit wiring method is not illegal, but buys you nothing but headaches. It's very difficult to wrestle, and takes up way too much space (counts as a round wire of the wide dimension). It's not going to bring you closer to running comms and power in the same conduit.

As a rule, NM cable in conduit doesn't buy you any advantages at all. This is one warning that you may be barking up the wrong tree.

800.133 only affirms a case that's already allowed.

Elsewhere in NEC there is a rule that you can run low voltage or comms wiring in Class 1 methods, and commingle with power lines, if and only if the entire comms circuit, every inch soup to nuts, is wired in Class 1 wiring methods.

It's not even really an exception. You see, Class 1 wiring has no minimum voltage. If you want to install to mains spec and then run 6V on it, be my guest. Nothing says you can't use class 1 wiring to convey signal instead of power, and that's exactly what happens between some smart switches, for instance. The only exception being made is use of smaller than 14AWG wire. Here's an example:

We have a furnace which is built to include an air conditioner. It includes a 24V transformer. Power to the furnace uses the conduit wiring method as does power to the air conditioning unit; the route between these units is continuous class 1 wiring method. We can run the 18AWG, 24VAC air conditioning control cable through that conduit because the entire 24V circuit is insulated for mains voltage and entirely contained in a Class 1 wiring method. That's an open-and-shut case for the exception, right? Right?

Oh wait, the thermostat. That is not rated for mains voltage and the wiring to it uses a non-class-1 wiring method. Since its wires connect conductively to some of the aforementioned wires, this is no good. None of the circuitry can share conduit with mains wiring.

Presumably, you want your ethernet cables to exit class 1 wiring methods at a faceplate, then proceed via the decidedly not-class-1 ethernet cable to your most definitely not class 1 Ethernet card or dongle. So like my thermostat, your entire comms circuit is not in class 1 wiring. That is exactly what you can't do.

Also I believe Ethernet cable is not insulated well enough and not a large enough wire diameter.

Answer 2

The exception to 800.133(A)(2) does not allow you to put communication circuits in the same conduit as power circuits, it simply allows you to put the communications cables within 2" of power cables. 800.133(A)(1)(c) outright prohibits communications conductors from sharing raceways with power conductors (unless separated by a permanent barrier).

National Electrical Code 2017

Chapter 8 Communications Systems

Article 800 Communications Circuits

800.133(A)(1)(c) Electric Light, Power, Class I, Non-Power-Limited Fire Alarm, and Medium-Power Network-Powered Broadband Communications Circuits in Raceways, Compartments, and Boxes. Communications conductors shall not be placed in any raceway, compartment, outlet box, junction box, or similar fitting with conductors of electric-light, power, Class I, non-power-limited fire alarm, or medium-power network-powered broadband communications circuits.

Exception No. 1: Section 800.133(A)(1)(c) shall not apply if all of the conductors of electric-light, power, Class I, non-power-limited fire alarm, or medium-power network-powered broadband communications circuits are separated from all of the conductors of communications circuits by a permanent barrier or listed divider.

Answer 3

Basically all of the wire has to be rated for the voltage on the power circuit.

In your case, in residential, most likely 300 volt wire. Unless you put the Cat6 in a separate raceway or wire everything category one. (And that Cat6 cable gets very expensive.)

That is what exception 1 is saying.

Good luck!