When running thermostat wire for 75 feet, which wire gauge should a technician use to avoid voltage drop?

To determine the appropriate wire gauge for running thermostat wire over a distance of 75 feet, it’s important to consider the concept of voltage drop, which occurs when the electrical resistance in the wire causes a loss of voltage over long distances. Using a wire that is too small in gauge can result in insufficient voltage reaching the thermostat, which may cause the heating system to operate inefficiently or not at all.

The most suitable choice here is #16 AWG wire. This gauge strikes a balance between being thick enough to minimize voltage drop while still being flexible and manageable for thermostat applications. Generally, for low voltage applications like thermostat wiring, keeping the voltage drop under 5% is important for reliable performance; #16 AWG wire is sufficient to maintain acceptable voltage levels at 75 feet, especially when dealing with typical low current loads.

The other gauges serve different purposes: #14 AWG is thicker and would be appropriate for higher current applications but may be cumbersome for a thermostat connection, while #18 AWG and #20 AWG are more suitable for shorter distances in low-load applications. However, at the 75-foot distance, #18 AWG may not adequately prevent voltage drop, making it less effective than #16 AWG in this specific scenario.