A critical part of AC double rail track circuit testing is verifying the integrity and balance of the impedance bonds. This is especially important in electrified areas where traction return current may be present.
If the impedance bonds are damaged, improperly connected, or imbalanced, unwanted traction current may affect the receiver. This can create unsafe or unreliable indications, including the possibility of a false clear condition.
Specialized testing equipment may be used to measure the impedance of each bond and confirm that the bonds are within acceptable tolerance. Proper bond balance helps protect the track circuit signal and supports reliable train detection.
Broken rail detection is another important test. A break in one rail should interrupt the AC signal path and cause the receiver to de-energize, indicating an occupied or unsafe track condition.
Broken rail detection can be tested by simulating a rail break and observing whether the receiver drops as expected. This fail-safe response is important for railroad safety.
Regular maintenance testing should include visual inspections of insulated joints, impedance bonds, wiring, connections, and track circuit equipment. Maintainers should look for damage, corrosion, loose wiring, poor bonding, and signs of deterioration.
Electrical testing should also be repeated periodically to confirm that the track circuit continues to operate within specified limits. All test results should be documented and compared with previous readings to identify trends before they become failures.