The operation of electrical appliances receiving electrical power from an electrical system may be indirectly monitored using monitoring units engaged with outlets on branch circuits of the electrical system. Electrical systems providing power to appliances to be monitored in accordance with the present invention may comprise split phase alternating current systems, tri-phase systems, or any other type of electrical system. Known loads may be applied to calibrate the monitoring system. The monitoring system may measure the power consumption of appliances operating on the electrical system and/or detect possible fault conditions. The monitoring system may be distributed across multiple monitoring units and other computing devices. Output devices may be used to output a summary of the power consumption or other operation of monitored electrical appliances.