Electric protection enclosure comprising a mobile gas venting flap

The invention relates to a protection casing (10) of a medium-voltage device, comprising a cover plate (20), which can move between the space from a position blocking an opening (16) in the casing (10) to a position where the cover plate (20) will not block a channel formed by the opening (16). The cover palte (20) is fixed to a panel (14) of the casing through a coupling device. When the internal pressure of the casing (10) is lower than a preset value, the coupling device keeps the cover palte (20) in a closing position. The coupling device (30) is designed to limit the stroke through the movement of a sliding cover plate (20), and includes a deformable element which can be deformed when the internal pressure of the casing (10) is larger than the preset value.