Pressurized enclosures with simplified control units - a concept for zone

1 Pressurized enclosures with simplified control units - a concept for zone 2 

Requirements for zone 2 p-apparatus are given in IEC 60079-14 (identical with EN 60079-14), overtaken as German Standard VDE 0165 Teil 1/1998-08 and IEC 60079-2/4th edition. In addition, clause 23 of EN 50021/1999-04, overtaken as German Standard VDE 0170/0171 Teil 16/2000-02, is under consideration. EN 50021 refers to electrical apparatus, Group II, category 3G. 

The advantage of pressurization - compared with other protection techniques, e.g. restricted breathing enclosure - is given by a positive pressure differential permanently maintained in the apparatus interior. Load cycles of the p-apparatus do not affect this pressure differential, and by this way, a cooling-down period caused by reduced or no-load conditions cannot cause an inverted pressure differential (the pressure of the surrounding atmosphere is somewhat higher compared with that in the apparatus interior) which may force the backstream of environmental flammable atmosphere into the interior of an apparatus. Pressurization guarantees safe operational conditions completely independent of load cycles. 

Compared with pressurized apparatus for zone 1 application, some benefits are given for zone 2 application  

These facts enable a more simple layout and construction of the safety device and related parts for controlling and monitoring the pressurization. 

---