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The Siemens WL arc resistant low voltage switchgear design was tested and certified without the need for an exhaust plenum.
An optional exhaust plenum and exhaust ductwork is available but not required to meet IEEE C37.20.7. IEEE C37.20.7 contains testing procedures and guidelines for internally vented (inside the electrical room) and externally vented. The testing arrangement and requirements are different for each venting method. If the venting is to be internal, the minimum electrical room dimensions must be duplicated for the test. IEEE C37.20.7 Paragraph 5.1.1.f states the following – “If the design incorporates an exhaust system that will vent pressure directly out of the room, no room simulation is necessary.” Additionally, the placement of thermal test indicators (indicators designed to evaluate the thermal effect of arc flash gases) are different for internally and externally vented systems. In summary, IEEE C37.20.7 supports and defines the testing requirements for internally and externally vented systems and most (if not all) arc resistant low voltage switchgear manufacturers offer both designs.
