Hermetically Sealed Electrical Equipment

Specifically designated electrical equipment can be manufactured so that its internal components are completely sealed. This eliminates the possibility electrical arcing components or circuits can contact combustible vapors or gases. 

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In areas where electrical equipment is exposed to contaminants, the selection of equipment whose contacts are oil-immersed or hermetically sealed can increase reliability and equipment life. Similarly, providing environmentally-controlled equipment rooms can greatly increase equipment life at locations where contaminants are prevalent. In offshore and other areas exposed to salt, type 316 stainless steel is often preferred over types 303 and 304, which will pit with time. Likewise, in similar locations, equipment fabricated from galvanized steel will corrode much more rapidly than equipment hot-dip galvanized after fabrication. 

Acceptable protection techniques for electrical and electronic valve accessories used in specific class and division locations include explosion-proof enclosures intrinsically safe circuits nonincendive circuits, equipment, and components dust-ignition-proof enclosures dusttight enclosures purged and pressurized enclosures oil immersion for current-interrupting contacts and hermetically sealed equipment. Details of these techniques can be found in the National Electrical Code Handbook, available from the National Fire Protection Association. 

F4 laboratories are required to have solid walls, floors and ceilings in which all openings (air ducts, electrical sockets, etc.) are hermetically sealed in order to ensure physical isolation and to prevent the escape of biomaterials from the laboratory. They are also required to have a separate ventilation system which maintains a negative air pressure. The laboratory must also have equipment for decontaminating the air before it is expelled into the atmosphere. 

ASSURANCE OF CONTINUOUS LONG-TERM CAPABILITY OF HERMETIC SEALS ON INSTRUMENTATION AND ELECTRICAL EQUIPMENT... 

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