Cabling, Conductors and Wiring Practices
Conductors and terminations
Signal wiring uses listed conductors suitable for the environment: wet or dry, direct burial, raceway, and temperature rating. Keep signal, neutral, and equipment grounding conductors distinct. Follow the contract color code and label both ends. Terminate with listed connectors, torque to the manufacturer’s value, and avoid nicked strands. Splices belong in accessible pull boxes or cabinets, not inside conduit. Leave a drip loop and service slack at equipment.
Voltage drop and fill
NEC informational notes recommend limiting branch-circuit voltage drop to 3 percent and total to 5 percent for reasonable efficiency. Calculate with the round-trip length and the conductor resistance. Derate for temperature and conduit fill.
Worked example: A 120 V, 5 A load is 300 ft from the source. 12 AWG copper has about 2.01 ohms per 1,000 ft. Voltage drop = 2 × 0.300 kft × 5 A × 2.01 = 6.03 V, or 5.0 percent-right at the total limit. Using 10 AWG (about 1.24 ohms/1,000 ft) gives 3.7 V, or 3.1 percent, which is a better design. The reasoning: the return conductor counts, so double the one-way length.
Traps: shared neutral; wrong color code; no slack; aluminum-to-copper contact without a listed connector; splices in conduit; missing labels; ignoring temperature derating.