18-2 Thermostat Wire is a specific type of electrical wire commonly used for wiring thermostat systems in heating, ventilation, and air conditioning (HVAC) applications. The "18-2" designation refers to the wire gauge and the number of conductors.

Here's what each component of the wire designation represents:

18: Wire Gauge - The number "18" indicates the gauge of the wire. In this case, it represents 18 AWG (American Wire Gauge), which refers to the thickness or diameter of the wire. A lower gauge number corresponds to a thicker wire.

2: Number of Conductors - The number "2" indicates the number of separate conductors within the wire jacket. In this case, it means there are two insulated conductors within the wire sheath.

The thermostat wire typically consists of two insulated conductors twisted together within an outer jacket. The insulation is usually color-coded, with commonly used colors being red and white or red and black. The specific color coding may vary, so it's important to check the wire's labeling or documentation for the correct identification of each conductor.

Thermostat wire is used to connect the thermostat to the HVAC system, allowing the thermostat to control the heating or cooling functions. The red wire typically carries the 24-volt power supply to the thermostat, while the white (or black) wire is used to transmit signals from the thermostat to activate the heating or cooling system.

The wire's insulation is typically made of PVC (Polyvinyl Chloride) or other suitable materials to provide electrical insulation and protection. It is designed to withstand the voltage and temperature requirements of thermostat applications.

When installing 18-2 Thermostat Wire, it is important to follow proper wiring practices, including ensuring secure connections, using appropriate connectors or terminal blocks, and adhering to local electrical codes and regulations.

In summary, 18-2 Thermostat Wire is a two-conductor electrical wire with 18 AWG gauge commonly used for wiring thermostat systems in HVAC applications. It allows for the connection between the thermostat and the heating or cooling system. The wire's insulation and color coding may vary, so it's essential to consult the wire's documentation for accurate identification and proper installation.