Why should millivolt wiring be isolated from line voltage wiring?

The importance of isolating millivolt wiring from line voltage wiring primarily revolves around preventing unwanted interactions between different voltage systems. When millivolt wiring, which typically carries low voltage and is used in applications such as millivolt gas valves, is run parallel to line voltage wiring, there's a risk that the higher line voltage could induce a voltage into the low-voltage wiring. This induced voltage could potentially interfere with the operation of devices that rely on the precision of the millivolt signals, leading to improper functioning or erratic behavior in systems like gas appliances.

By keeping these two types of wiring separate, you create a safer environment where the reliability and accuracy of the millivolt system are maintained, reducing the risk of electrical faults or failures. This isolation is an essential practice in electrical installations to ensure the effective operation of the devices attached to these circuits.