Different types of impedance bonds are used depending on the railway electrification system, traction current requirements, track circuit frequency, and signal system design.
The main differences between impedance bonds include their construction, current carrying capacity, winding arrangement, frequency response, and how they connect to the rails.
A single impedance bond is one of the basic types. It uses a winding to allow traction return current to pass while helping block or limit the signaling current used by the track circuit.
A center-tapped impedance bond has a center connection point. This center tap can help balance traction return current between the two running rails and is commonly used in double-rail track circuit arrangements.
Double impedance bonds may be used where additional current carrying capacity or increased impedance is required. These arrangements are selected based on the electrical design of the railroad system.
Tuned impedance bonds are designed for specific signaling frequencies. They may include additional electrical components that improve isolation between adjacent track circuits.
Wee-Zee bonds are commonly associated with DC traction systems using AC track circuits. Their purpose is to allow DC traction return current to pass while blocking or limiting AC signaling current.
Specialty impedance bonds may also be used for systems such as audio frequency track circuits, impulse track circuits, or other specialized train detection systems.
The correct impedance bond must be selected for the system it serves. Using the wrong type can cause poor track circuit operation, traction return problems, or unsafe signaling conditions.