Line bushings are used to electrically connect equipment in potentially explosive atmospheres. The connection is always established either between a flame proof enclosure and an enclosure of another type of protection in accordance with DIN EN 60079-0. Alternatively, two flame proof enclosures are connected. Thus cables are protected from direct contact. Varying with the design, line bushings can be used in intrinsically safe, measuring, control of energy circuits. Line bushings that do not feature cables, i.e. they are only cast, can be used to seal flame proof enclosures of the “d” type of protection. Via line bushings, holes or threads can be closed. If the system is to be extended at a later time, if required, line bushings containing cables can replace the existing sealed ones.