Troubleshooting impedance bonds requires understanding how one failed bond can affect both the traction power system and the railroad signal system.
One common problem is high DC resistance. This can reduce traction return current flow, create voltage drops, cause heating, or allow current to seek an unsafe return path.
High resistance can be caused by loose connections, corroded terminals, damaged cables, broken rail bonds, poor hardware, or internal damage inside the impedance bond.
Incorrect inductance can also create signaling problems. If the bond no longer has the correct electrical characteristics, the track circuit may not see the proper impedance at its operating frequency.
This can cause AC track circuits to become unstable, weak, falsely occupied, or falsely clear depending on the failure and circuit design.
Low impedance at signaling frequencies can allow signal energy to leak into adjacent track circuits. This can reduce track circuit separation and create unreliable train detection.
Overheating is another serious warning sign. It may indicate excessive traction return current, poor connections, internal bond damage, wrong current rating, or abnormal current flow through the bond.
Visual inspection should include checking for corrosion, loose cables, cracked cases, burned terminals, melted insulation, damaged mounting hardware, water intrusion, and signs that the bond has been struck.
When troubleshooting, technicians should follow railroad maintenance standards, use approved test equipment, compare readings to known good values, and protect themselves from energized traction power equipment.