Gas Heat ESCO Practice Exam 2025 – Comprehensive All-in-One Guide for Exam Success!

When running thermostat wire over a long distance, such as 75 feet in this case, it's crucial to consider voltage drop to ensure the proper functioning of the system. Thicker wires have lower resistance, which helps minimize voltage drop over longer distances. The American Wire Gauge (AWG) system is used to measure the diameter of wires, with smaller numbers representing thicker wires.

In this scenario, using an 18 AWG wire is the correct choice because it has lower resistance compared to the thinner wires like 20 AWG. Thicker wires like 12 AWG might be too excessive for a thermostat application and could be more challenging to work with. On the other hand, 16 AWG wire is also a thicker option, but it is not as optimal as 18 AWG for this specific purpose.

Therefore, choosing 18 AWG wire for running thermostat wire over 75 feet is the best option to prevent voltage drop and ensure the proper operation of the system.