The basics of explosion protection - STAHL - #29

Text version of the page

direct entry, the connecting cables are entered directly into the flameproof enclosure. Only cable glands that have been specially certified for this purpose may be used for this type of entry. 29 5.3 Methods of Installation Essentially, three systems are used for electricalinstallations in hazardous areas: indirect entry, the cables and linesare conducted via cable glands into a connection chamber in the type of protection “Increased Safety” and connected to the terminals also pro- vided in “Increased Safety”.From here, the individual wires are conducted via flameproof bushings into the flameproof enclosure.The cable bushings are installed by the manufac-turer, with the result that, by contrast with direct entry, a routine test of the factory wired flameproof enclosure can be made. The installation engineer need only open the connection chamber for the connection, not the flameproof enclosure.In the case of > Cable systems 1. Cable system with indirect entry > Cable systems are mainly used in Europe. For this, high-quality cables are laid uncovered. It is only in areas in which mechanical damage could be expected that they are laid in conduits that are open at both ends.In the case of 2. Cable system with direct entry > 3. Conduit system The technical design of the electrical apparatus used with the individual types of installation is accordingly different.Only the conduit system or mineral insulatedcables (MI) are permitted in the USA for all appli- cations in Class 1, Division 1 in accordance with NEC 501-4, whereby the mineral insulated cables are mainly used as heating lines and fire resistant signal and control lines. Certain types of cable and line are also permitted in Division 2. A com- parison of the various systems is shown below.
Fig. 8: Methods of Installation worldwide:Left: Cable system with indirect entry; Centre: Cable system with direct entry; Right: Conduit system R.STAHL explosion protection