Ethernet Wiring

Technically, this would meet building code.

3M Fire Barrier 1.45 in. x 6 in. Moldable Putty Stix MP+ Flexible 76

It can be installed in the air return ducting. You will need to use plenum fire rated jacketed cable though.

Other options for running the cable?  Is the floor in the room  pad and carpeted? It is possible the cable could be installed around the wall base trim under the carpet. Between the carpet tack strip and the wall base trim. 

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Interesting...

CAT5,  4 pair UTP Ethernet cable was first introduced in 1995.

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  CAT3,  4 pair UTP Ethernet cable was first introduced in 1991. Good for voice, not so much for data though, as I recall. 

Installed miles of RG62/U coax cable in the 1980s for desk top dumb terminals. 

Also installed some RG58 coax cabling in the 1980s.

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@lovehifi22 ,

Project status?   

The cable would be inserted into the duct about 15’ away from the furnace plenum.

I assume a straight shot through a 6" dia round supply duct to a ceiling mounted outlet vent register? (Naturally the ceiling register would be remove when installing a fish tape to pull in the data cable.)

Good luck if you first have to travel through a main supply duct to the tap off for the 6" dia round branch duct that feeds the ceiling register.

FWIW, I would recommend you purchase the data cable from Blue Jeans Cable. They will make you a cable cut to length and install RJ45 plugs on each end of the cable. Cable will then be tested to make sure it meets specs standards. Not just a wire mapping test.

Protect both connectors so they are not damaged during installation. 

FWIW:

NEC (National Electrical Code) 300.22(B) does not allow an Ethernet cable to be installed in HVAC supply air fabricated duct work for the use as a raceway.

Even the exception doesn’t allow its’ use as a raceway.  

300.22(B) Ducts Specifically Fabricated for Environmental Air.

Exception: Wiring methods and cabling systems, listed for use in other spaces used for environmental air (plenums), shall be permitted to be installed in ducts specifically fabricated for environmental air-handling purposes under the following conditions:

(1) The wiring methods or cabling systems shall be permitted only if necessary to connect to equipment or devices associated with the direct action upon or sensing of the contained air, and

(2) The total length of such wiring methods or cabling systems shall not exceed 1.2 m (4 ft).

https://www.electricallicenserenewal.com/Electrical-Continuing-Education-Courses/NEC-Content.php?sectionID=276

NEC does allow Ethernet cables to be installed in air return plenums provided the cabling is UL Listed plenum rated. (Or, NRTL Listed meeting UL)

FWIW, If the OP does install the Ethernet cable in the supply duct work he should install an insulated  grommet or bushing in the cut entry hole in the metal ductwork to protect the outer jacket, and internal insulated conductors from being cut, damaged, by the supply air movement through the duct chaffing the cable at the sharp cut entry hole of the metal duct work. 

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@mswale Said:

It is perfectly safe to run cat6 inside ducting.

In your opinion...

It’s not NEC code compliant in HVAC supply air ducts. 

06-11-2025 at 07:11am

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