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Thermostat Wire

We call thermostat wire that cable that runs from the HVAC system to the thermostat on the wall. It is weird stuff in three ways:

It is usually difficult to find solid (non-stranded) wire in cables with more than two conductors when the wires are 20 gauge or larger. This is because cables get stiff and difficult to work with due to the solid conductors. Apparently this doesn't bother the HVAC installers. (I guess ducting tin is even more stiff!)
The color coding is unique in the cabling industry. In order: White, red, green, blue, yellow, brown, orange.
It is not paired, and requires unusual wire counts: 5 and 7 conductors.

While you might get away with running other kinds of cable, you'll have the wrong number of conductors, with either the wrong gauge or stranding, and with a color coding that will not match the directions or the lables on the screw terminals of either the HVAC system or the thermostat.

18 Gauge Solid Conductor Wire
- 2 Conductor ("millivolt" heat only systems or damper motor control)
- 5 Conductor (Standard HVAC systems)
- 7 Conductor (Typical heat-pump systems)

18 Gauge Solid Conductor Wire

18 gauge thermostat cable is adequate for practically any residential application.

CAROL
A Division of General Cable
18 Gauge Thermostat Wire; 2, 5, & 7 Conductor

Manufacturer and jacket color may vary.

300 volt
UL Type CL2
Annealed solid copper per ASTM B3
Premium grade color coded PVC insulation
PVC jacket, white
Temperature range: -20°C - +105°C
Jacket marking: CAROL AWG TYPE CL2 (UL) 105°C SUNLIGHT RESISTANT - MADE IN USA
Applications: Thermostat control, heating and air conditioning installations, touchplate systems, burglar alarms, intercom systems, doorbells annunciator and bell systems, remote control units, signal systems, other low-voltage installations.
Color codes:
- 2 Conductor: White, Red
- 5 Conductor: White, Red, Green, Blue, Yellow
- 7 Conductor: White, Red, Green, Blue, Yellow, Brown, Orange
Packaging:
- 2 Conductor: 500' spool
- 5 Conductor: 250' spool
- 7 Conductor: 250' spool