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 50mA at 100A – 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 sensor does not have a load resistor built in, so in most cases it will be necessary to place a resistor across the output to convert the coil’s induced current to a very small measurable voltage.