A split core transformer (or non-invasive current sensor) is a form of current sensor that doesn’t require the existing power cable to be cut; instead this transformer clamps around a power cable. It measures the current by acting as an inductor and responding to the magnetic field around a current-carrying conductor. By reading the amount of current being produced by the coil, you can calculate how much current is passing through the conductor.

This version outputs approximately 1V at 30A – which makes it great for building your own energy monitor to keep your power usage down, or even building an over-current protection device for an AC load. This version has a built in burden resistor and terminates with a standard 3.5mm “headphone jack”. The clamp will fit over cables up to ~ 12mm in diameter.