Controller Cabinets, Power and Detection
Cabinet and power
Controller cabinets house the controller, conflict monitor, detector rack, terminal blocks, surge protection, and communications. NEMA TS 2 and ATC cabinet standards define interfaces and environmental performance. Power service includes a disconnect, overcurrent protection, grounding electrode system, and separate neutral and equipment ground. Do not bond neutral to ground at the cabinet; that creates a parallel return path. Battery backup or UPS may be required.
Detection
Detection may be inductive loop, video, radar, or magnetometer. Loops require correct saw-cut dimensions, lead-in twisting, sealant without voids, and testing. Video and radar need aiming and zone configuration.
Worked example: A 120 V, 10 A circuit runs 250 ft to a cabinet. With 12 AWG (2.01 ohms/1,000 ft), drop = 2 × 0.25 × 10 × 2.01 = 10.05 V, or 8.4 percent-too high. 10 AWG gives 6.2 V (5.2 percent), 8 AWG gives 3.9 V (3.2 percent). Select 8 AWG or reduce the load. The reasoning is the same round-trip voltage-drop calculation used for signal circuits, applied to the dedicated cabinet supply.
Traps: neutral bonded in the cabinet; missing surge protection; loop sealant voids; detection zone aimed at the wrong lane; no battery backup test; unlabeled terminal blocks.