Hall effect current sensor which is programmable through a connector

An apparatus for sensing electrical current flowing in a conductor includes a toroidal core formed of a ferric material and having a slot defining an air gap, a Hall Effect sensor integrated circuit positioned in the air gap for sensing electrical current flowing in a conductor received in a central aperture of the core, and a housing 34 enclosing the core and the integrated circuit. The integrated circuit can be programmed to set functions such as output offset, gain, temperature compensation and a current sensing range. The current sensor may be calibrated when applying a known current 10 from a current source 30. The polarity of the current source 30 may be reversed using a switch arrangement 16. The current sensor may be located in a plastic housing 34.