Abstract: Method and device to determine the threshold of resistance of an electric or electronic equipment to an external electromagnetic aggression, by simulating such aggression, the said equipment comprising at least two units joined together by way of a connection comprising shielded conductors.The invention is remarkable in that at least one passive injection element is inserted in the said connection, which element presents a known transfer impedance and comprises an external casing, inner conductors, and end connectors, so that said injection element ensures a continuity of the normal electric connections between the said units and that its external casing is electrically connected to the shielding of the said connection, in that the said equipment equipped with its injection element is subjected to the action of an electromagnetic testing field.