To minimize voltage induction from nearby power lines, which routing is best?

• A. Running parallel to power lines for long distances
• B. Crossing power runs at shallow angles
• C. Routing control wiring away from parallel power runs and crossing at 90 degrees
• D. Placing control wires near metal pipes

Answer: (C)

The main idea is to minimize magnetic coupling between power lines and nearby control wiring by how you route the conductors. Induced voltages are strongest when a control conductor runs parallel to a power line for a long distance, because the changing magnetic field from the line threads along the length of the wire and links with it. Crossing the power line at a right angle greatly reduces that linkage, so the induced voltage is kept to a minimum. Routing away from long parallel runs also cuts exposure and further lowers induction.

Crossing at a shallow angle would still leave substantial parallel exposure for a segment of the route, so it isn’t as effective as a 90-degree crossing. Placing control wires near metal pipes doesn’t solve the problem and can introduce safety and conduction issues, potentially allowing stray currents to travel through the pipes.

So the best approach to minimize voltage induction is routing control wiring away from parallel power runs and crossing them at 90 degrees.