The ohmic contact sensor is designed as an option for the electrical initial positioning of the workpiece surface to ensure the optimum height of the plasma torch during ignition and cutting. The consumables of the plasma torch are hardly subject to any mechanical stress because only a minimum effort is needed. When cutting thin sheets, the otherwise usual sagging of the sheet can be avoided. The signal generated from a short-circuit between plasma torch and workpiece is galvanically isolated several times at an interface and is made available for use by external control units.