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I added a bypass humidifier to my forced air furnace. The control panel is mounted to the return duct, and the wiring runs from the panel into the furnace fan compartment.

Wires run from the water panel, from the control panel, and from the outdoor temp probe. I understand you don't generally have to protect/conduit 24V wire and all the originally existing thermostat wire is exposed (but neat). But while I tried to be neat and made most wire connections inside the furnace, it's kind of a mess with wires twisting how they like and 4-5ft of wire that runs along the side of the downflow return duct is totally unsecured.

How would the pros run it? I'm not a neat freak and I think I'm OK code-wise, but I'd like it to not look like a "homeowner special hack job".

In that same vein, what about securing the 1/2" vinyl drain tube? I can zip tie the end to the floor drain, but the tube wants to bend & twist, and it isn't neat at all right now.

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    A picture would help. But generally zip-tie to other wires. For the floor drain, consider running some of it with rigid PVC.
    – Shimon Rura
    Commented Dec 11, 2017 at 19:46
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    @ShimonRura never, never attach thermostat wiring or anything else to mains electrical wiring, cable, conduit, raceway, gutter, etc. That is close to the #1 codevio where furnaces are concerned. HVAC installers don't think anything of it because it doesn't violate their code,
    – Harper - Reinstate Monica
    Commented Dec 11, 2017 at 20:32
  • @Harper thanks. That's surprising though, on the AC install at my house the city electrical inspector insisted that the thermostat wire to the outdoor condenser unit be zip-tied to the conduit supplying line voltage, instead of zip-tied to the refrigerant lines. Can you point me at a code reference that might clarify?
    – Shimon Rura
    Commented Dec 15, 2017 at 16:49
  • 300.11b raceways not to be used as means of support for anything else unless designed for that purpose... 800.52e communication cables not to be attached to conduit or raceway... And (always) 110.12 must be used according to listing's labeling and instructions.
    – Harper - Reinstate Monica
    Commented Dec 15, 2017 at 18:45

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Use screw mount zipties, and attach them to the metal ductwork with sheet metal screws. To repeat what Harper said, do not ziptie your low voltage wires to electrical conduit or cables.

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    Nifty, thanks. Speaking of Harper's comments, there's an existing 16V 18-2 power cable that twines like a vine up a steel conduit snake housing mains power. I didn't put that in but it sounds like it's a code violation. Something I should probably fix while I'm at it? What do I do if low voltage "wants" to run right next to mains conduit? Is the concern induced current in the low voltage wire, or shorts between mains & low voltage?
    – user76412
    Commented Dec 12, 2017 at 0:15
  • I would just leave the doorbell wire as is. It's getting power down at the furnace and while it's technically not okay per code but it makes sense for it to be hanging off that conduit for 5 feet. If you replace the furnace you're going to have to do something with the doorbell transformer anyway, so it's probably fine to leave it.
    – Dotes
    Commented Dec 12, 2017 at 1:28
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    @PatrickShyvers induction is a potential issue not in EMT conduit... But the bigger problem is that electrical cabling, conduit, etc. is not listed, tested or labeled to be a hanger for anything else. If the thermostat wire, why not the evaporator drain line? It gets out of hand real fast, I've seen it.
    – Harper - Reinstate Monica
    Commented Dec 12, 2017 at 16:54

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