The present invention relates to diagnostics using auxiliary metering devices. Systems and methods for diagnosing a device, such as an appliance (702), using a secondary meter device (704) that measures electrical characteristics related to usage of the appliance within a HEM network (700) and provides such data to a residential energy controller (706) or the like. The auxiliary instrumentation device may include one or more sensors (724), such as current transformers, Rogowski coils, shunt resistors, or Hall effect sensors, etc., for collecting data related to active power consumption, reactive power consumption, line frequency, line voltage, etc. , power factor, lead / lag voltage-current comparison, and apparent power.