National Wire 18AWG/8C-100 8 Conductor 18 Gauge Solid Copper Thermostat Cable. This item is a 100 ft length of thermostat wire. The wire consists of 8 strands of coated, color-coded copper wire to connect a thermostat to heating, ventilation and air conditioning systems. An 8 conductor wire allows you to control a complex HVAC system. The eight wires include power, heat, cooling, fan, heat mode reversing valve, cool mode reversing valve, 2nd stage heat and common all harnessed in a single jacket.