Traffic Signal Controllers, Cabinets, and Electronics
Controller and cabinet families
The exam samples knowledge of NEMA TS 1/TS 2, ATC 2070, and legacy 170 controllers, and the cabinets that house them. Know the power path: service disconnect, main breaker, transformer, controller, load switches, flasher, and conflict monitor. Verify voltages and terminal assignments against the cabinet wiring diagram before changing anything.
Electronics to verify
- Conflict monitor/MMU: supervises field outputs for conflicting greens, red failure, and low voltage; a fault forces flash. Program channels to match phasing.
- Load switches: isolate controller outputs from field wiring; a shorted load switch can create a conflict.
- Detection inputs: rack cards, loop inputs, and video or radar contacts must be labeled and assigned to the correct phase.
- Communications: twisted pair, fiber, or Ethernet; surge protection and grounding must be intact.
- Housekeeping: door gasket, filtered fan, desiccant, labels, and wire management.
Worked example
After power restoration, the intersection flashes all-red and the MMU logs a conflict on phase 4. Do not simply reset the MMU. Put the cabinet in flash, remove the phase 4 load switch, and test the field wiring; a shorted load switch or crossed green output can hold the conflict. Replace the failed component, verify no conflict with a test box, then return to automatic and record the event.
Traps
Resetting a conflict monitor without finding the fault; replacing the controller when the MMU is reporting a field-wiring problem; mixing TS 1 and TS 2 pinouts; failing to verify input voltage; and bypassing a door switch or surge suppressor.