Case 13930

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


Non-Intrusive Load Monitoring (NILM), Current Sensor, Circuit Breaker, JFET


Various power distribution systems

  • Current wrap-around magnetic field sensors are impractical for some retrofit applications.
  • Specific safety regulations related to electrical devices


The invention provides a new sensor for non-intrusive power monitoring that measures current flow in a circuit breaker without modification of the breaker panel and the circuit breaker itself. The sensor consist 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 JFET modulator circuit for transmitting information 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 that it can monitor multiple loads from a central location.


    A solution for low-cost, non-destructive retrofit of any circuit breaker panel for centralized power monitoring.

  • Professor Steven B. Leeb (Department of Electric Engineering and Computer Science, MIT)
  • John J. Cooley (Department of Electric Engineering and Computer Science, MIT)
  • Al-Thaddeus Avestruz (Department of Electric Engineering and Computer Science, MIT)
  • Zachary A. Clifford (Department of Electric Engineering and Computer Science, MIT)

Intellectual Property:

US Patent Number 8,344,724, issued on January 1, 2013



Last revised:November 8, 2010

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