A Retrofit 60-Hz Current Sensor for Non-intrusive Power Monitoring at the Circuit Breaker


This device enables Non-Intrusive Load Monitoring technology to allow fine-grained power monitoring in new settings. This technology can be applied to various power distribution systems and legacy. 

Problem Addressed

Current wrap-around magnetic field sensors are impractical for some retrofit applications and are further constrained by specific safety regulations related to electrical devices. The technology presented is an alternative to the wrap-around magnetic field sensor. It measures the current in the utility feed by sensing the resulting magnetic field at the face of the main circuit breaker in a standard breaker panel, where the Line and Neutral are already separated. These devices function with enough signal to noise ratio to provide time and frequency domain reconstructions of the current in the main circuit breaker. A major challenge that is overcome by the system presented here is that of communication through the steel breaker panel door, which must be closed to comply with safety regulations. 


The invention provides a new sensor for non-intrusive power monitoring that measures current flow in a circuit breaker without modifying the breaker panel or the circuit breaker itself. The sensor consists of three main parts: an inductive pickup for sensing current from the breaker face, an inductive link designed to transmit power through the steel breaker panel door, and a passive balanced Junction Gate Field-Effect Transistor (JFET) modulator circuit for transmitting information through the inductive link. The novel JFET does not require a DC power rail to mix the incoming carrier with the 60 Hz current signal sensed from the breaker. The sensor may be interfaced with a spectral envelope load detection system so it can monitor multiple loads from a central location. Non-Intrusive Load Monitoring (NILM) is an approach with a much lower sensor count than other device-specific monitoring systems. A NILM system identifies and monitors individual loads on a power distribution system by measuring the frequency content of transient events in the current signals from a centralized location. 


  • Versatile
  • Low cost
  • Non-destructive