Protecting the Low Voltage Wires to the AC
That brown-sheathed, low voltage wire from the air handler to the AC unit outside tells the contractor when to engage. This allows the high voltage to pass from one side of the contractor to the other, flowing on to the compressor and condenser fan motor. Without this low 24 volt communication, the AC won’t start. So, shouldn’t we protect that wire as much as possible from potential damage and UV rays? Isn’t it in the electrical code that we have to use some sort of perspective conduit with wiring outside the house? That’s what we’re going to talk about today on Fox Family Heating, Air Conditioning and Solar.
I’ve never heard of any low voltage wire used in residential heating and air conditioning that is rated for outdoors, including wet or damp conditions. So why, when I service equipment and go on HVAC inspections around the Sacramento area, do I find dried up, brittle sections of thermostat wire simply taped to the suction line from the wall to the AC?
I spent hours researching this online. I’m having the hardest time finding the citation in the National or California Electrical Code that describes when to protect the low voltage wire in outdoor conditions, such as an air conditioner installation. So, if you ARE aware of the part of the book that talks about this topic, please let me know in the comments section down below. As always, I admit, I don’t know all the answers, but I’d really like to know if you wouldn’t mind sharing.
What the Code Says
Article 725 of the National Electrical Code talks about this type of control wiring. And I can’t find one part in there that says Class 2 wire (like the 24 volt thermostat wire we use in residential HVAC) must be protected by or enclosed in conduit.
On one hand, the stat wire is not rated for outdoor use, let alone in wet or damp conditions which leaves it exposed to damaging elements. Possible hazards are endless — landscapers who use weed eaters, a dog’s incessant need to chew up things in the yard, the ultraviolet rays coming from the sun, the arid nature of summer and winter all dry up just about anything that stays outside long enough — the list is long.
On the other hand, installing stat wire inside the liquid-tight conduit really doesn’t make it a dry environment either. And according to what I’ve found (and not found) in my research, a dry environment isn’t even needed for class 2 wiring anyway.
Protecting the Wire
But ever since my first HVAC installation, I was required by my foremen to protect the stat wire with ½” seal-tight conduit, so I’ve always taught my techs to do the same. It undeniably protects the wire better than just strapping it to the suction line without seal-tight and leaving it exposed to the elements. It’s also in the best interest of the customer to ensure the stat wire lasts as long as the AC itself.
If the stat wire dries up and becomes dry and brittle, it takes almost nothing, like a bump by the lawn mower, to expose the bare wire within the sheathing and result in the wrong wires touching each other. This shorts out the low voltage system, rendering it inoperable. This requires the homeowner to call a service technician to come out to troubleshoot and fix the issue.
But it’s not in the code books. So, when I see newly built residential neighborhoods with exposed stat wire at the AC, I cringe, but I have to remind myself it’s not actually required.
The Tightest Provision Gets Enforced
If it’s not required, why do so many inspectors write up correction letters to us for doing retrofit changeouts, and not protecting the stat wire with some sort of conduit? The answer may be, “that’s the way they want it.” Remember, local jurisdictions can tighten the rules as they deem necessary. And the tightest provision of any code is the one that gets enforced.
If you really wanted to push the issue, you could ask the code inspector (nicely) where you could find the source of their local rules; one that lists their requirements which are more restrictive than the National Electric Code.
I get that there ARE several sections in the code book that say wiring must be protected from potential damage, but it never mentions it specifically when it comes to Class 2 control wiring.
With that said, let’s take a look at what it would take to upgrade your customer’s low voltage wiring to a more protected state. It doesn’t require too much work. The cost of the parts is minimal compared to the protection you’ll provide to the stat wire in the future.
Take the old dried up stat wire off the existing suction line insulation. Cutting it back to about six inches from the wall will allow you to splice on new wiring to run through the conduit. Once it’s been wire nutted and taped for protection, leave a little bit of the colored wires there. If a future technician has to troubleshoot it, they can search back to your splice and easily see the wires that are connected. This will give them the option of using that third wire as an alternate.
Shove the wire nuts into the penetration of the wall where it comes out and slip the new wire through the conduit. Fasten the conduit to the unit. Then strap it to the rest of the lineset and high voltage conduit going to the AC. This makes for neat and clean workmanship of your repair, which IS required by the electrical code.
The next time you see exposed thermostat wire coming from the wall to the AC, think about what’s right for your customer. If you’re a homeowner, it shouldn’t be too expensive to have your local HVAC company do this work on your system.
And, as always, whether dealing with high or low voltage electricity, there are inherent dangers and mechanical failures that can happen when dealing with them. So, let’s leave it to the professionals.
Once again, I’d love to hear your thoughts on this topic, so leave a comment down below.
Thanks so much for stopping by and we’ll see you on the next blog topic!