BNC Probe Cable, Passive for CT1 and CT2 Current Probes. The Tektronix P6041 is a Probe Cable and provides the connection between the CT1 and CT2 current transformers and a BNC oscilloscope input. A 50 ohms termination is required to terminate the cable when connected to a high-impedance (1 MOhm) oscilloscope input. One probe cable can be used to monitor several current transformers that have been wired into a circuit.