Chapter 5 – Signal Wiring

Publisher Summary This chapter describes methods to minimize electrical interference in signal and ground wiring and properly install and terminate signal wiring. Multi-pair cables should contain at least one spare set twisted-pair wires. It is recommended that each cable contain at least 20 percent spares. Electromagnetic interference (EMI) can be caused by such devices as radios, intercoms, AC power lines, motors, and high capacity switches. Inductive coupling interference can occur when signal wiring leads are routed close to power lines or other high current leads. It also can occur when other equipment is not sufficiently separated from power lines, transformers, rotating equipment, or other high power machinery. If a magnetic field from AC power leads is a source of interference, the leads can be twisted to reduce field strength. When signal leads and power leads must cross, they should do so at right angles. Assuming the installation does not use intrinsic safe barriers, low-level signal lines should be continuous from signal source to receiver. The signal lines should not run parallel to high-current or high-voltage lines.