Low-voltage wire is found all throughout the house and outdoors. It's used for lights, doorbells, and it even carries high-speed internet signals. Whether you're wiring a new device or you've stumbled on an unusual wire stapled to the baseboard, you might be dealing with one of a broad variety of low-voltage wires.
What Low-Voltage Wire Is
Low-voltage wiring is insulated wiring with non-metallic sheathing that carries 50 V or less of electricity. By comparison, standard wall outlets found in rooms and hallways are 120 V.
Low-voltage wiring is commonly used in the home for thermostats, doorbells, TV cable, and network cable. Low-voltage wire is most often found outside of the home with low-voltage landscape lighting systems.
Low-Voltage Wire Gauges
American Wire Gauge (AWG) is a standard way of identifying the thickness or gauge of electrically conductive wire. Lower numbers indicate thicker wires; higher numbers indicate thinner wires.
AWG refers to single-strand, solid wire. For stranded wire—common with low-voltage wiring—AWG is still used. The diameter of the multiple strands when added together in cross-section is equivalent to the single-strand, solid wire designation.
Wire in 14- and 12-gauges is used around the home for higher voltage devices like lights and outlets. Wire gauges for low-voltage devices range from 12-gauge to 24-gauge wire.
Common Types of Low-Voltage Wiring Around the Home
Thermostat Wire
Thin 18-gauge wire in bundles of two, three, four, or five wires is used to connect wall thermostats to remotely located HVAC units (furnaces and ACs).
Doorbell Wire
Also called bell wire, long runs of thin 18- or 20-gauge wire in bundles of two are used to connect wired doorbells to the doorbell chime or base unit, often located far away in a central location in the house. It is also used to connect the transformer to the system.
Landscape Light Wiring
Double-strand 12-, 14-, and 16-gauge wire is used for low-voltage landscape wiring. The wire is typically buried in direct contact with the earth.
Lights along the run spike into continuous-run wire with special low-voltage push-fit wire connectors, eliminating the need to cut the wire and splice in the lights.
Network Wiring
CAT5, CAT5e, CAT6, and CAT6A are network Ethernet cables designed for carrying broadband internet.
- CAT5: The earliest type of network cable dating back to 1999, CAT5 wire was quickly supplanted by its better-performing variant, CAT5e cable. CAT5 cable sometimes carries voice and video data, as well.
- CAT5e: The "e" stands for "enhanced," so CAT5e cable, with its 24-gauge twisted pair wires, carries data at up to 10 times faster speeds and longer distances than CAT5 cable. CAT5e is usually tested at up to 100 Mhz frequencies, though some manufacturers make claims up to 350 Mhz.
- CAT6: CAT6 cable can carry more bandwith than CAT5e and is able to process frequencies up to 250 MHz. Its absolute maximum speed is 10 gigabits per second under ideal conditions, at lengths up to 165 feet.
- CAT6A: The "A" stands for "augmented" with this improved CAT6 cable capable of 500 MHz speeds (10 Gigabits per second) or higher, at lengths up to 328 feet.
TV Cable
RG-6 coaxial wire with a single 18-gauge wire running down the center is used for cable TV.
RG-59 is an older general-purpose coaxial cable with 22-gauge wire. Since other cables are better for higher frequency signals, RG-59 cable is mainly found outdoors for CCTV security cameras, for analog TV antennae, or buried underground.
Phone Wire
Low-voltage Cat-3 phone wire with 24-gauge wires, four or six to a bundle, is still found in many homes. Cat-3 cable can carry both voice and data (up to a bandwidth of 16 MHz).
How to Identify Low-Voltage Wires
Low-voltage wiring has some characteristics that differentiate it from wiring for higher voltage devices. Often, but not always, low-voltage wire is made of thinner gauge wires. Sometimes, it is buried in direct contact with the earth or stapled directly to exposed locations (higher voltage wire should never be exposed).
Low-voltage wiring typically has a thinner sheathing or jacket. For example, 12-gauge wire is used for both 120 V household devices and for lower voltage landscape lights. But the sheathing is different between the two: tough PVC sheathing 19 mils thick for the household current and thinner, more pliable vinyl sheathing for the landscape wiring.
A better indicator but still not definitive: low-voltage wire is often identified by stamps on the side of the sheathing or jacket.
So, phone wire might be stamped with "CAT 3 24 AWG," along with other words and numbers. Or a network wire may be stamped with "CAT 6 RoHS CM 24 AWG" (RoHS means that the wire is free of lead and other hazardous substances).
Low-Voltage Wire Safety Risks
Low-voltage wiring typically is not a safety hazard, but it can be. Low-voltage wiring often cross-connects with devices that do carry higher voltages.
Also, low-voltage wiring can carry enough power to create an electric arc. All it takes is one spark in contact with flammable or combustible liquids, solids, or vapors to create an explosion or start a fire.
Do-it-yourselfers, electricians, or anyone working with low-voltage wiring should exercise caution and treat low-voltage wiring as if it were higher-powered wiring.