Case including: - a metal terminal (10, 12, 14) having a bottom edge, a top edge and side faces (50, 52) each extending from the bottom edge to the top edge, - a box comprising: - a hole for inserting the metal terminal inside the casing, - a groove suitable for gripping the side faces of the metal terminal to secure it to the casing, this groove comprising first and second side walls (82, 80) made of plastic which extend, opposite each other, from a bottom of the groove to distal lips (90, 94) which define an elongate opening via which the metal terminal is inserted into the groove, - a cover which can be moved between an open position and a closed position in which the cover seals the opening in the box, - a locking system capable of holding the lid in its closed position, characterised in that: - the first wall is a flexible wall displaceable by elastic deformation between: - an inclined rest position in which the space between the distal lips (90, 94) is greater than the thickness of the terminal, thus limiting friction between the metal terminal and the first and second walls (82, 80) when the metal terminal is inserted into the groove, and - a tightened position in which the first and second walls (82, 80) grip the side faces of the metal terminal inserted in the groove to secure it to the casing, - the cover has a corner with an inclined face capable of: - when the cover is moved from its open position to its closed position, to move the flexible wall from its inclined position to its constricted position by positive engagement, and - holding the flexible wall in its tightened position as long as the cover is locked in its closed position by the locking system. - a metal terminal (10, 12, 14) having a bottom edge, a top edge and side faces (50, 52) each extending from the bottom edge to the top edge, - a box comprising: - a hole for inserting the metal terminal inside the casing, - a groove suitable for gripping the side faces of the metal terminal to secure it to the casing, this groove comprising first and second side walls (82, 80) made of plastic which extend, opposite each other, from a bottom of the groove to distal lips (90, 94) which define an elongate opening via which the metal terminal is inserted into the groove, - a hole for inserting the metal terminal inside the casing, - a groove suitable for gripping the side faces of the metal terminal to secure it to the casing, this groove comprising first and second side walls (82, 80) made of plastic which extend, opposite each other, from a bottom of the groove to distal lips (90, 94) which define an elongate opening via which the metal terminal is inserted into the groove, - a cover which can be moved between an open position and a closed position in which the cover seals the opening in the box, - a locking system capable of holding the lid in its closed position, - the first wall is a flexible wall displaceable by elastic deformation between: - an inclined rest position in which the space between the distal lips (90, 94) is greater than the thickness of the terminal, thus limiting friction between the metal terminal and the first and second walls (82, 80) when the metal terminal is inserted into the groove, and - a tightened position in which the first and second walls (82, 80) grip the side faces of the metal terminal inserted in the groove to secure it to the casing, - an inclined rest position in which the space between the distal lips (90, 94) is greater than the thickness of the terminal, thus limiting friction between the metal terminal and the first and second walls (82, 80) when the metal terminal is inserted into the groove, and - a tightened position in which the first and second walls (82, 80) grip the side faces of the metal terminal inserted in the groove to secure it to the casing, - the cover has a corner with an inclined face capable of: - when the cover is moved from its open position to its closed position, to move the flexible wall from its inclined position to its constricted position by positive engagement, and - holding the flexible wall in its tightened position as long as the cover is locked in its closed position by the locking system. - when the cover is moved from its open position to its closed position, to move the flexible wall from its inclined position to its constricted position by positive engagement, and - holding the flexible wall in its tightened position as long as the cover is locked in its closed position by the locking system.