• Mains AC: non-invasive | OpenEnergyMonitor
  This method of measuring mains AC electrical energy use is quite nice, it doesn't require any breaking of the mains wire, which makes it nice and safe, you just clip-on to the wire a sensor called a current transformer (CT) that measures the current flowing through either the live or neutral mains wire. It does this by measuring the magnetic field that surrounds the wire, created by the current. The simplicity of just clipping on the sensor means that it can be used to measure the electrical energy used by the whole house. It a method used by many commercial devices that you can buy.
  in Hus & Hem > Home Automation with current electrical measure measuring wire

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