How To Protect an Air Conditioner Low Voltage Wire

how to protect low voltages wires to the AC

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 those low voltages wires to the AC from potential damage and UV rays?  Doesn’t the electrical code    require some sort of conduit with wiring outside the house?  That’s what we’re going to talk about today on Fox Family Heating, Air Conditioning and Solar.

Ratings for Low Voltage Wire

I’ve never heard of any low voltage wire that’s rated for outdoors, including wet or damp conditions being used in residential heating and air conditioning.  When I service equipment and go on HVAC inspections around the Sacramento area, why do I find dried up, brittle sections of thermostat wire?  They’re 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 appropriate citation in the National or California Electrical Code.  The citation in question describes when to protect the low voltage wire in outdoor conditions, such as with an air conditioner installation.  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.  But I can’t find anything stating that Class 2 wire (as in the 24 volt thermostat wire used 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 list is long.

On the other hand, installing stat wire inside the liquid-tight conduit really doesn’t make it a dry environment either.  A dry environment isn’t even needed for class 2 wiring anyway, according to what I’ve found (and not found) in my research.

Protecting the Low Voltage AC Wire

Ever since my first HVAC installation, protecting the stat wire with ½” seal-tight conduit was a must.  My foreman insisted, 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, exposed to the elements.  Ensuring stat wire lasts as long as the AC is also in the best interest of the customer.

If the stat wire dries up and becomes dry and brittle, it takes almost nothing to expose the bare wire within the sheathing.  This can 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 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.

A Wiring Upgrade

Consider what it would take to better protect your customer’s low voltage wiring to the AC.  It doesn’t require too much work.  The cost of the parts is minimal compared to the future protection you’re providing to the stat wire.

Remove the old dried up stat wire from the suction line insulation.  Cutting it back to about six inches from the wall will allow you to splice on new wiring.  Once it’s run through the conduit, wire nutted and taped for protection, leave a bit of the colored wires there.  A future technician will thank you.  A quick search back to your splice will easily reveal the connected wires.  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.  Then 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 neat and clean workmanship of your repair IS required by the electrical code.

Looking Ahead

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.

As always, whether dealing with high or low voltage electricity, there are inherent dangers and mechanical failures that can happen.  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!

Don’t miss our video on this topic:

How to Repair An Air Conditioner

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2 Comments

  1. Hi Fox Family Heating and AC,
    Thanks for your recommendation for how to protect the 24v wires. I have completed the task within .5 hr. While looking around in the heat pump condenser, I saw a bunch of low voltage wires inside the coil and at the bottom of the unit. They are exposing to the weather and have no conduits/wire protection. Some of the wires are faded out due to UV ray/weather. These wires have no sight of damage so far but my questions are: Why are these wires not protected? These wires condition came from Trane manufacture since new. Is there any reason for this? Should I or can I buy the type of conduit (not water tight) that will allow me to wrap these wires so they are protected and will last a long time ? Please let me know what your thought are or provide any recommendation for how to address these situation?

    Thank you very much for your time
    Loc Ng

    • Great question. The low voltage wires inside the unit and within the area of the compressor and fan that you are seeing do not need to be protected by conduit. Sometimes they do rub through if they are tied directly to a copper pipe. If that is the case I use two zip ties to create a gap between the pipe and the wire.


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