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I was planning to get 3/4" conduit (Carlon ENT/Smurftube) to run network cables through the house.

Just how many CAT6 cables can safely fit into 3/4" conduit?

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  • Try it and see. I think low voltage cabling has different rules for things like conduit fill factor.
    – William S.
    Aug 12, 2015 at 17:33
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    There isn't any official fill codes for Cat6 cabling that I know of. But really it comes to practical purpose. The only pratical reason to run Cat6 cables in conduit through a home setting is to make removal and re-cabling easier. Because of that, you need to have the cables loose in the conduit. The longer the conduit, the less cables you will be able to run and pull them through easily.
    – diceless
    Aug 12, 2015 at 18:30
  • Yes, the purpose of the conduit is to upgrade in the future
    – Slav
    Aug 12, 2015 at 18:36
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    40% of 3.5 inches (the long edge of a 2x4) is 1.4". So you can run at least 1" low voltage flexible raceway. That's pretty good size. Also, everywhere you run this stuff, I would consider making it a home-run back to a central wiring cabinet so you don't end up trying to over-stuff the conduits. Or if you're talking about a big enough area, use more than one cabinet, and you can run multiple conduits between the cabinets to leave yourself plenty of room to pull more cables later. And pull power separately to every cabinet.
    – Craig Tullis
    Aug 13, 2015 at 1:10
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    @WarLoki it's not for the ISP/Internet speed, it's for the internal network. I have small kids = tons of home iPhone videos. Copying them from my PC to wife's PC to NAS takes time, streaming to TV without hiccups is another concern. They are already huge uncompressed MOV files. New phones coming out can record in 4K resolution. CAT5e can just about do 1Gbps. CAT6 can do 1Gbps easily (PCs, NAS all have a 1Gbps NIC), and it can do 10Gbps for short distances. Sooner or later, we will get 10Gbps consumer devices.
    – Slav
    Aug 17, 2015 at 0:07

5 Answers 5

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This depends on whether you are using pre-assembled cables or not. The following images were made using The Engineering Toolbox's Smaller Circle in Larger Circle Tool to find the optimal packing.

If using bare cable (No Connectors)

Using a 6.5mm (0.256) Diameter cable, you can fit only 5 cables per conduit. 0.256" Dia cables

However, this assumes the cables are perfectly circular and non-deformable. If you assume you can deform the cables, or you use a slightly smaller cable, you can fit up to 7 without destroying the cables. 0.249" Dia cables

If using pre-assembled cable

However, you will likely be using connectorized cables. Assuming a 0.5"x0.5" connector head (I measured one I had laying around), you'd be lucky to fit 2. 0.256" Dia cable with connector

Conclusion

If running connectorized cables, you can probably get away with 2, max. However, if using bare cable, you can comfortably fit 5, but can potentially fit up to 7 without completely squishing the cables. Using the ratio of areas, we could theoretically fit ((.75^2)/(.25^2)) = 9 cables, but if we abide by the National Electrical Code's 40% rule, this translates to only 3.6 cables (more accurately, ((0.203)/(pi*.125^2))=4.1). Therefore, if you go with bare cable, by code, you can only legally run 4 cables through the conduit. (I'm not sure how the NEC calculates this 0.203 although their math allows up to 4 cables - my math would limit us to only 3 cables). Although I do not endorse illegal activity, I would feel comfortable running up to 5 cables in that size conduit.

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  • Nice tool, very handy
    – Slav
    Aug 12, 2015 at 20:43
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    You'll never actually be able to pull 7-9 cables through the conduit, even 5 is probably going to be a tough pull (unless you've got a lot of lube, and the right tools).
    – Tester101
    Aug 12, 2015 at 20:57
  • I'd argue 2 would be a practical limit for easy-pulling. Also, I don't think you'd ever want to use connected cables. For in-wall installs, you'd be connecting the cables to wall plates, so wouldn't have a use for the connector in the first place.
    – DA01
    Aug 12, 2015 at 21:10
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    @DA01 Only 2 network cables in a 3/4" conduit? I've definitely pulled at least 3 through 1/2" EMT in the past without too much trouble. By "connectorized" cables, I'd imagine this poster is thinking more of things like HDMI cables than Ethernet/Cat6 cables, in which case, yeah, it's all going to be painful. You can pull the appropriate HDMI cable unterminated and put connectors (or wall plates) on the stuff after the fact, though.
    – Craig Tullis
    Aug 13, 2015 at 1:09
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    What in the world Before you do that, you better ask a question about PoE. PoE makes it a power cable, and now you're at 40% fill max, 30% if there are only 2 cables. Also you are allowed to use pipe actual diameter rather than trade size; that buys you a bit with some pipes.
    – Harper - Reinstate Monica
    Feb 17, 2020 at 14:50
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When it comes to data (Cat6) cable it in not so much about the number of wires you can fit in to the conduit, because the more you get in the conduit the more the speed of the information could degrade. I have always put no more then 4 Cat6e in a 3/4in Conduit. So pick the best cable for your job and then the correct size of conduit or run more then one 3/4in.

The following is from, http://www.datcominc.com/edit/files/catalogues/Mohawk%20Conduit%20Fill%20Guide.pdf

Mohawk Fill Guide

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  • Nice guide. Can you comment: considering I will use a conduit, does that mean I don't need plenum cables? The conduit itself is what provides the fire-"protection" right?
    – Slav
    Aug 13, 2015 at 3:36
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    @Slav The plenum rating doesn't typically apply inside of walls, if that's where you're running this. If your conduit is in a plenum area (used as part of the return air system), you have to use metal conduit and/or plenum-rated cable. But if you're running the conduit in an area where you're allowed to run PVC conduit, plenum-rated cable isn't a requirement anyway and you could use riser cable. If riser cable is used in a plenum area, you could end up sucking acidic smoke through the HVAC system and into occupied space, making it harder for people to see to get out, and/or suffocating them.
    – Craig Tullis
    Aug 13, 2015 at 8:07
  • @Craig thanks, I didn't realize there was a difference between "in-wall", "riser" and "plenum". Did more research thanks to your comment. Now I know
    – Slav
    Aug 13, 2015 at 14:24
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If you're following National Electrical Code, you'll need to know the actual size of the cable. In the Notes to tables section of chapter 9, there are two important notes.

(5) For conductors not included in Chapter 9, such as multiconductor cables,the actual dimensions shall be used.

(9) A multiconductor cable, optical fiber cable, or flexible cord of two or more conductors shall be treated as a single conductor for calculating percentage conduit fill area...

So assuming you'll be pulling more than two cables, according to Table 1 of chapter 9 you'll have to use the 40% fill column from the conduit fill tables.

You'll need to know the cross sectional area of the cable you're installing, and the type and size of conduit you want to use. Then you'll look up the allowable fill for that size conduit, using the 40% fill column of the applicable table.

3/4" Electrical Nonmetallic Tubing (ENT), has a 40% fill value of 0.203 in.².

Then you'll divide the value from the table, by the area of the cable (and drop the remainder). This will tell you how many cables you can pull though that conduit.

Example

According to this document, the outside diameter of UTP Category 6 cable is 0.25 in.

0.25 in. / 2 = 0.125 in.
A = pi * r² = pi * 0.125² = 0.0490873852 in.²
0.203 in.² / 0.0490873852 in.² = 4.1354820423

So if you're pulling similar sized cable through 3/4" ENT, you'd be able to pull 4 cables through the conduit and be code compliant. Though in reality, without lube and special cable pulling tools. You'd probably only be able to pull 2 or 3, unless it's a short straight-ish pull.

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    @Slav That document is only good for that specific cable, the size may (and probably will) vary from manufacturer to manufacturer. I simply used the values for example purposes.
    – Tester101
    Aug 13, 2015 at 0:09
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For what it's worth, I recently ran 5 in 3/4" conduit and it was a tough pull. However, it had a couple bends to work through. I used foam lube and fish tape to help ease the friction. I do worry about degrading the signal and may remove one. I'd say 4 should be more than doable without concern of damaging wire.

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You're allowed to overpack it to practical fill limits, but only if it's pure comms cables. NO PoE. See NEC 820.110 and 830.110. Your peril if you overfill it is you'll have to pull so hard you rend the cables, or they'll chafe and tear at burrs in the conduit. But on datacomm cables, it doesn't create a safety problem.

As soon as you put any power in there, even low voltage, you're now dealing with power cables. See Article 725.3(A). And the NEC conduit fill rules apply, i.e. 40% for 3 or more cables (30% for 2 cables).

As always, you cannot put higher voltage power in any conduit with datacomm.

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  • > "As always, you cannot put higher voltage power in any conduit with datacomm." I imagine you are still allowed to put PoE (44-57V) with other (non PoE) datacomm cables in the same conduit -- what constitutes higher voltage here?
    – Travis
    Jun 20, 2021 at 10:41
  • @Travis I have wondered that myself. By the raw spec, PoE seems to spit in the eye of NEC. However, given the number of countries that rely on El NEC, and the general skill at design deployed in setting standards like PoE, I am sure they worked out an angle for compliance. Possibly current-limiting.
    – Harper - Reinstate Monica
    Jun 21, 2021 at 19:20

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