An electric field-reducing insulating layer is described for an inductive coil. In some examples, a first coil having at least one first winding is arranged for being driven at a first voltage. A solid insulating layer is adjacent the first coil and has a first surface facing the first coil. The first surface of the solid insulating layer has a first groove between the first winding and the insulating layer, having a width that is smaller than a diameter of the electrical wire. The first groove forms a pocket between the first winding and the solid insulating layer.