Various embodiments herein relate to power distribution networks for optically switchable windows. In some embodiments, a system for monitoring and maintaining a power distribution network of optically switchable windows of a site is provided. The system includes a control panel monitor which is configured to determine a control panel voltage and current at a terminal of a control panel. The system further includes sense circuitry which is configured to determine a first window controller voltage and current for a first window controller of a plurality of window controllers. The system further includes one or more controllers which are configured to generate voltage network data based on a combination of the control panel voltage and current and the first window controller voltage and current. The system then determines an error condition in the power distribution network based on the voltage network data.