Diagnostics using sub-metering device

A system and method for performing diagnostics on a device, such as an appliance (702), using a sub-meter device (704) that measures power characteristics related to usage of the appliance within a HEM network (700) and provides such data to a home energy controller (706) or the like. The sub-meter device can include one or more sensors (724), such as a current transformer, Rogowski coil, shunt resistor, or hall effect sensor, for collecting data relating to at least one of real power consumption, reactive power consumption, line frequency, line voltage, power factor, leading/lagging voltage-current comparison, and apparent power, etc.