Non-hardening electrical putty, also known as duct seal compound or mastic, is the preferred material for sealing wire entries directly inside the box. Just peel off layers until the module fits. One area efficient Roxtec seal can replace up to 32 traditional cable glands. This includes the rear wall, side panels, doors, door handle a d ventilation grille with climate filter for the air intake. It prevents the uncontrolled movement of air, moisture, and. BOX SHELL is a patented enclosure system that completely seals electrical junction boxes — eliminating air infiltration, reducing energy loss, and meeting LEED, WELL, and Passive House standards.