Moisture layers with low layer conductivity are characterized by low power dissipation, e.g. 50 mW for the epoxy resin model post insulator under investigation. Under those conditions, no temperature-related dry zones appear, but micro partial discharges (PDs) cannot be excluded. The appearance of these discharges depends on the voltage stress, the surface properties, and the relevant climatic conditions. Experiments on moisture layers with low layer conductivity have been performed in test setups under well-controlled conditions. Typical patterns of the PD behavior could be established and simulated with the help of simplified equivalent-circuit diagrams. >