Much of what is required for explosion proof design is covered in our article What does explosion proof mean? However, there are fine points and details regarding the individual components that allow units to function safely in hazardous areas.
Our NEMA 7 enclosures are available only for use in our InPac and PressurePac units, and are not sold separately.
Specific Systems makes available NEMA 7 compliant control panels, junction, and housings for applications in hazardous (classified) environments. NEMA 7 enclosures can be integrated into Specific Systems HVAC and Pressurization units for use in hazardous locations classified as Class I, Division/Zone 1 or 2, Groups B, C, or D as defined in NFPA 70.
NEMA 7 enclosures work as a containment for any spark or arcing that could occur between electrical connections. The enclosures quarantine the electronics, thereby separating the potentially hazardous air outside from any spark that may occur, and removing the risk of explosion or fire.
In an area being declassified by an HVAC/Purge & Pressurization unit, the electronic equipment in the protected area is required to be in a NEMA 4 enclosure. This is usually the case. However, when the unit goes into purge mode, anything in a NEMA 4 enclosure must be depowered, while electronics enclosed in a NEMA 7 are permitted to stay active.
Multiple junction boxes are also available as an additional option. For example, 24V is used in Specific Systems’ control panels, while a higher voltage (230, 480, 575, etc.) is used to actually run the equipment. Separating these boxes allows for a higher level of safety for technicians, going beyond applicable requirements requirements.
NEMA 7 panels installed on Specific Systems units are manufactured from corrosion resistant, light weight, copper-free aluminum. The external sealing flange allows for easier access to electrical components, and the integrated mounting slots are cast on for safety.
In applications where a NEMA 7 enclosure is required, all electrical connections must be made inside the enclosure in order to meet specifications under NFPA articles 497 and 500. Enclosures are constructed meet and exceed these requirements. External flanges on all NEMA 7 enclosures allows easy and maximum access to electronic components.
Because each Specific Systems HVAC unit is individually designed, the enclosures are sized directly to the number and type of options on the unit.
Motors themselves can not be contained in a NEMA 7 enclosure, so how can they be used in a hazardous area?
The most obvious possible ignition point is where wires meet. In hazloc motors, electrical connections are housed in an enclosure specifically designed to meet the needs of each rating (temperature code, number of threads, watertight seal, etc.). Further, motors for Class I areas are designed with the same principles as NEMA 7 enclosures, to ensure any gases created during explosions inside of the casing are cooled enough to not cause a secondary explosion outside of the housing.
Even though Class I is the rating most commonly thought of when 'hazardous' areas are discussed, there are vastly different requirements for Class II motors, which is just as dangerous a classification. For instance, Class II areas typically require a lower temperature rating to prevent auto-ignition of dust that builds up on the motor casing.
In each of our units destined for a hazardous location, we utilize motors that are UL Listed and approved for use in each specific type of hazard.