Different Types of HVAC Cable
There are a few main types of cable used for HVAC systems. Knowing the differences can help you select the proper one for your application:
Thermostat Cable
Thermostat cable, also called low-voltage cable, is used to connect HVAC control systems like thermostats to the indoor unit. It has two or more conductors insulated with PVC. 18/2 and 18/3 types are common for basic thermostat wiring. Go with plenum-rated cable if running through air ducts as it is less likely to emit toxic gases if exposed to fire.
High-Voltage Cable
High-voltage or line voltage cable is required to connect the indoor unit to the outdoor compressor unit. It has three insulated conductors for live, neutral and ground wiring and is rated for at least 600V. Make sure to use cable rated for outdoor use as it withstands moisture, oils and vibration better.
Communications Cable
HVAC Cables is newer communicating systems use cable designed for low voltage communications between components like thermostats, indoor units and wireless remotes or sensors. It has conductors plus communication pathways and is usually plenum rated for safety. Cat5e Ethernet cable or proprietary communication cables work well.
Conductor Quality and Insulation Rating
The quality of conductors and insulation used directly impact cable performance and longevity in HVAC applications. Consider these factors when choosing:
Conductor Material - Copper conductors conduct electricity far better than aluminum and are less prone to corrosion over time in humidity.
Conductor Size - Use wire size recommended by manufacturer as undersized wiring leads to voltage drop and overheating risks.
Insulation Rating - Cable rated for outdoor use, moist locations and higher temperatures hold up better long-term. Look for labels indicating wet location, sunlight resistance, -40°C to 105°C range.
Insulation Material - PVC insulation is common but less durable long run. Consider cross-linked polyethylene (XLPE) or thermoplastic polyurethane (TPU) insulation for harsher climates.
Proper Sizing for Applications
Selecting cable that matches the size and power needs of your HVAC system is another must. Consider:
- Distance between indoor/outdoor units - Longer runs require larger cable to minimize voltage drop.
- System size in tons - Larger units draw more amperage so need thicker cable.
- Circuit protection rating - Cable must be appropriately rated to protect against overcurrent from breakers/fuses.
- Indoor/outdoor unit connections - Line voltage cable for units. Low voltage cable for thermostats, sensors.
Choosing cable at least one size up from minimums ensures sufficient current carrying capacity and future-proofs the system. Consult manuals for exact sizing charts.
Additional Requirements for Specific Applications
Some HVAC applications also require certain cable types and features:
- Duct installations - Must use plenum-rated cable certified as low smoke, low toxicity.
- Buried lines - Must withstand moisture and be sunlight/chemical resistant with suitable jacketing. Direct burial type works well.
- Rooftop units - Use UV resistant, flexible rubber or synthetic cable jacket suitable for exposed outdoor installations.
- Commercial systems - May need flame retardant or fiber-optic communication types. Follow commercial building codes.
With so many options to consider, contractors should evaluate individual needs and the specific usage environment to determine the best HVAC cable for each unique installation. Proper cable selection goes a long way in ensuring safe, reliable system performance for years.
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