A system for detecting contact and proximity between ablation electrodes by sensing changes in voltage morphology of non-activated electrodes, the system comprising: a catheter, which is configured for insertion into a body of a patient, the catheter comprising at least a first electrode, a second electrode and a third electrode, which are disposed at a distal end of the catheter and are configured to contact tissue within the body; a pulse generator, which is configured to apply one or more bipolar ablation pulses between the first and second electrodes (30a, 30b), for ablating the tissue in contact with the first and second electrodes (30a, 30b); and a controller, which is configured to: (i) control the pulse generator to apply the one or more bipolar ablation pulses between the first and second electrodes (30a, 30b), and (ii) detect that a distance between (i) at least one of the first and second electrodes, and (ii) the third electrode, is smaller than a distance threshold; characterized in that: the controller is configured to receive a signal indicative of a voltage, measured between the third electrode and a reference during application of the ablation pulses, the distance is detected by detecting that the voltage violates a predefined criterion, and the controller is further configured to issue a notification in response to detecting that the voltage violates the predefined criterion. a catheter, which is configured for insertion into a body of a patient, the catheter comprising at least a first electrode, a second electrode and a third electrode, which are disposed at a distal end of the catheter and are configured to contact tissue within the body; a pulse generator, which is configured to apply one or more bipolar ablation pulses between the first and second electrodes (30a, 30b), for ablating the tissue in contact with the first and second electrodes (30a, 30b); and a controller, which is configured to: (i) control the pulse generator to apply the one or more bipolar ablation pulses between the first and second electrodes (30a, 30b), and (ii) detect that a distance between (i) at least one of the first and second electrodes, and (ii) the third electrode, is smaller than a distance threshold; (i) control the pulse generator to apply the one or more bipolar ablation pulses between the first and second electrodes (30a, 30b), and (ii) detect that a distance between (i) at least one of the first and second electrodes, and (ii) the third electrode, is smaller than a distance threshold; characterized in that: the controller is configured to receive a signal indicative of a voltage, measured between the third electrode and a reference during application of the ablation pulses, the distance is detected by detecting that the voltage violates a predefined criterion, and the controller is further configured to issue a notification in response to detecting that the voltage violates the predefined criterion. the controller is configured to receive a signal indicative of a voltage, measured between the third electrode and a reference during application of the ablation pulses, the distance is detected by detecting that the voltage violates a predefined criterion, and the controller is further configured to issue a notification in response to detecting that the voltage violates the predefined criterion.