Abstract: By a test vessel, a test enclosure is created immediately surrounding the zone of the line or cable harness to be inspected by detection. This enclosure is sealed off before detection-inspection and an internal atmosphere is substituted by at least a partial gas substitution with a test gas or a test gas mixture with a lower disruptive discharge voltage than that of air. This test method permits detection of faulty lines with greater distances between the faulty line, the test electrode, and the corresponding counter-electrode. A corresponding pliers-type device for the sectional detection of a line or harness, or a stationary vacuum seal-tight testing chamber capable of performing the same detection may be used. The method is suitable also for a local detection when the test vessel is created and formed by the installation object itself (e.g., an aircraft fuselage).