Gas Fitter Practice Test

Why should millivolt wiring be isolated from line voltage wiring?

1. The line voltage wire will overheat the low voltage wiring

2. The resistance of the millivolt wiring will be increased

3. The current in the low voltage wire will be reduced

4. The line voltage will induce a voltage into the millivolt wiring

The correct answer is: The line voltage will induce a voltage into the millivolt wiring

Isolating millivolt wiring from line voltage wiring is crucial primarily because line voltage can induce an unwanted voltage into the millivolt wiring. This induction can cause false readings and erratic behavior in devices that rely on millivolt signals, which are typically used for more sensitive applications such as gas control systems and pilot lights. Line voltage operates at a much higher voltage level, which can interfere with the lower voltage signal of the millivolt system. When these two types of wiring run in proximity without proper isolation, the electromagnetic interference from the line voltage can couple into the millivolt wiring, leading to inaccuracies and potentially damaging the components involved. The other choices, while they address aspects of the wiring systems, do not fully capture the primary concern associated with the interaction between different voltage levels. The overheating of low voltage wiring and resistance considerations are not fundamental issues when discussing the necessity of isolation, and the current reduction does not relate directly to the primary risk of voltage induction from line sources. Thus, emphasizing the issues surrounding induced voltage provides a clearer understanding of why isolation is essential.