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Fireproof Electric Enclosures

Image of an electrical enclosureFireproof enclosures provide a solution for shielding electric components in potentially explosive environments when airtight sealing is impractical or impossible. Although some types of electrical equipment can be hermetically sealed to protect them from external hazards, the majority of industrial electric power systems cannot be reasonably shielded in such a way. An apparatus that is placed inside an enclosure that is not airtight will often pull in atmospheric air when it is turned off and cooling. Internal temperature fluctuations may also permit the infiltration of external elements, and this can present a serious risk for systems that operate in environments containing combustible substances in the atmosphere. Lighting devices are especially prone to this problem because they have a high level of temperature variation between “on” and “off” settings, while electric motors face a similar risk due to the clearance needed for their drive shafts. Fireproof and flameproof enclosures address these issues, enabling vital electric equipment to maintain performance without sacrificing safety requirements.
 
The principles of fireproof electric enclosure do not focus on resisting the effects of a surrounding fire, but on preventing the spread of ignited flammable substances in the first place. Fireproofing involves placing electrical equipment within an enclosure that does not need to be sealed, but is still able to minimize the risk of inflaming explosive gases or other combustible materials before, during, and after operation. In addition, this type of enclosure is also intended to prevent an ignited mixture from spreading beyond the enclosure and damaging other machinery. In essence, a fireproof electric enclosure functions as a type of pressure vessel in which any openings or gaps in the seal can effectively trap flames before they escalate into a more significant threat.
 
Fireproof Design
 
There are a great number of variations in fireproof enclosure design, each depending on application requirements and the dimensional and operational parameters of a shielded device. However, certain basic design principles are shared by the majority of fireproof industrial enclosure systems, including:
 
  • Cables and connectors do not have direct entry into the fireproof enclosure.
  • External flange surfaces display strong metal-to-metal bonding or form a vented joint that does not exceed a maximum gap allowance.
  • Rubber or other materials that may undergo deterioration are not used to seal joints.
  • All externally facing joints and flanges are machined and installed with a preset minimum distance between the outer and inner sides of the enclosures.
  • Any fasteners used to secure covers are hooded.
  • Shaft and spindle bearings maintain a minimum length and a maximum radial clearance according to application requirements.
 
The specifications for each of these characteristics vary depending on the fireproofing project at hand, but rigorous and careful testing are always used to determine the enclosure’s effectiveness. One of the required tests involves identifying the maximum pressure that could possibly be produced from a gas explosion inside the enclosure, and then exposing the enclosure to slightly higher pressure in order to evaluate its protection levels. A similar test is used to verify whether or not an explosion within the enclosure will ignite a combustible atmosphere and spread fire to external systems.
 
Fireproof Enclosure Standardsfireproof enclosure
 
Structural integrity is one of the most critical characteristics in fireproof enclosure effectiveness, making it important for an enclosure to be tamper-proof and highly reliable. Installing and repairing an enclosure requires special training and certification, and the process should closely follow all safety protocols and manufacturer recommendations for components. The cables and conduits used to connect fireproof electrical equipment also play an important role in reducing the risk of ignition, although fireproof standards for these devices vary between different countries. For example, in the U.S., flameproof openings must be built using conduit type fittings with tapered threads, while Germany requires cables to be used in any openings. A common practice involves having a terminal enclosure attached to or surrounding a fireproof housing. This terminal enclosure adds additional levels of protection from short-circuiting and prolonged exposure to electric arcing, both of which can cause internal ignition in a fireproof system that does not have a terminal enclosure.

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