A system for use with multiple electrodes coupled to respective spines of a probe includes multiple switches connected to the electrodes and configured to short different respective first subsets of the electrodes to each other and different respective second subsets of the electrodes to each other per different respective settings of the switches. The system further includes a processor configured to control the switches so as to alternate through the settings and, for each of the settings, cause a power generator to apply a voltage between the shorted first subset and the shorted second subset while the probe is deployed within a body of a subject. Other examples are also described.