Setting up an AC double rail track circuit requires several key pieces of equipment. Each component has a specific purpose and must work together to provide reliable train detection.
Insulated rail joints are used to electrically isolate the track circuit from adjacent track sections. These joints define the limits of the track block and help keep the track circuit signal within the intended section.
Impedance bonds are used in electrified territory to allow traction return current to pass through the rails while helping protect the AC track circuit signal. They are an important part of many AC double rail track circuit installations.
An AC power source, usually supplied through a transformer or similar device, provides the alternating current signal for the track circuit. The voltage and frequency must match the requirements of the receiver or relay.
An AC receiver or AC-sensitive relay detects the track circuit signal. When the track is clear, the receiver remains energized. When a train shunts the rails, the signal drops and the receiver indicates occupancy.
Feeder cables, bonding wires, surge protection, lightning arrestors, and calibration equipment may also be used. These components help maintain a reliable electrical path, protect equipment, and support proper setup and testing.