This Part 2/3 of this Article is a continuation of Part 1/3, published previously
Indirect cable entries into “Ex” metal enclosures with “explosion-proof” (Ex “db”) types of protection with “increased safety” (Ex “eb”) junction boxes, with combined Ex “db eb IIC Gb” protections provide, among others, the benefits of increased “Ex” field service facilities for the assembly, inspection and maintenance activities of automation, telecommunication and electrical equipment and installations in classified areas containing flammable gases.
As it could be verified in Part 1/3 of this Article, the system of DIRECT cable entries inside metal enclosures with type of Ex “d” protection can present undue “deviations”, resulting from failures of “Ex” field services, related to failures of “Ex” design, assembly, inspection and maintenance services in classified areas.
In this Part 2/3 of this Article on “Benefits of indirect cable entries into “explosion-proof” metallic equipment“, the characteristics of cable entries into Ex “d” metallic enclosures, through Ex “d” bushings and through the use of external terminal box, with Ex “e” type of protection (increased safety) are shown, as well as the benefits obtained, from the point of view of easy “Ex” assembly, inspection and maintenance, from the point of view of safety of instrumentation, automation, telecommunications and electrical installations in classified areas, arising from the use of the system of INDIRECT cable entries, in relation to the system of DIRECT cable entries into the interior of metal enclosures of equipment with type of protection Ex “d” (“explosion-proof”).
INDIRECT cable entries into metal “explosion-proof” (Ex. “d”) enclosures
Indirect cable entries, executed by combining different types of “Ex” protection in the same “Ex” component or equipment, started in the 1970s, with the increased safety enclosures (Ex “e”), installed as terminal boxes for INDIRECT cable entries into the interior of metal Ex “d” enclosures.
The combination of the Ex “de” protection types, using Ex “d” through bushings for the cable entry into the Ex “d” enclosures, provided significant gains in terms of easy installation and field maintenance services of these “Ex” equipments, which no longer require the installation of sealing units, nipples, thread adapters, cable glands or “explosion-proof” male/female unions.
Indirect cable entries into Ex “d” enclosures by means of external terminal boxes of the increased safety type (Ex “e”) provide an effective and safe solution against the occurrence of undue “drifting” of field services in “Ex” assembly and maintenance, which could occur if direct cable entries were used.
Equipment such as this type, with Ex “eb” enclosures containing components with Ex “db eb” combined protection present, among others, the benefits of lower weight and the dispensability of installing cable glands, sealing units, male/female unions, nipples of the “explosion-proof” type or thread adapters. From the point of view of field services in classified areas, this equipment presents greater ease of assembly, inspection and maintenance, contributing to the reduction of undue “deviations” that are found during inspections of equipment and installations in classified areas of land and marine installations.
In the international IEC Technical Committee TC 31 (Equipment for explosive atmospheres), for example, where the IEC 60079 and ISO 80079 series international technical standards related to “equipment and installations in explosive atmospheres” are developed and updated, there are representatives of standardization bodies from participating countries who argue that “indirect” cable entries into Ex d metal enclosures should represent an installation “standard” to be adopted in all applicable cases.
In eventual cases, when there are no technical alternatives for the specification of equipment with metallic “explosion-proof” type enclosures, Ex “d” enclosures with THREADED lids and with INDIRECT inputs can be specified. In this type of “Ex” product, available on the market since the 1970s, the cables external to the equipment (cables installed by users) are connected to terminal boxes of the increased safety type (Ex “e”), not requiring the opening of the metallic explosion-proof enclosures, reducing the risk of human errors in field services for assembly, inspection or maintenance. Besides this, the Ex “d” enclosure in the versions with THREADED cover, dispenses the need for installation of a large number of screws for fixing covers on the flanges.
Examples of installation of metal enclosures of the “explosion-proof” type (Ex “d”), containing sparking devices, such as circuit breakers, contactors, relays, or fuses, with cable entry system in an INDIRECT way are shown below.
Examples of installation of Ex “d” type metallic enclosures containing sparking devices, with DIRECT cable entry into the interior of the metallic “explosion-proof” type enclosure by means of Ex “d” sealing units for conduits and Ex “d” cable glands and INDIRECT cable entry into the interior of the metallic “explosion-proof” type enclosure by means of Ex “eb” terminal box, external to the enclosure, by means of sealed cable (bushings)
The system of cable entries in an INDIRECT way, is basically composed of an assembly formed by an explosion-proof enclosure (Ex “db”), with passage to a terminal box of the increased safety type (Ex “eb”) through a sealed cable (bushing) of the “explosion-proof” type (Ex “db”).
Example of a factory sealed (bushing) cable gland of the “explosion-proof” type (Ex “d”) for instrumentation, power, control, telecommunications and automation circuit cables (including fiber optics)
Example of a factory sealed (bushing) cable gland of the “explosion-proof” type (Ex “d”) for instrumentation, power, control, telecommunications and automation circuit cables (including fiber optics)
Example of “Ex” equipment installation containing metallic enclosure of the “explosion-proof” type, showing detail of assembly of sealed bushing of the “explosion-proof” type (Ex “d”)
Some practical examples of “Ex” equipment installations containing “explosion-proof” (Ex “d”) metallic enclosures are given below, where the external cable entries into the interior of the Ex “d” metallic enclosure are not made “directly”, for example through Ex “d” cable glands or Ex “d” sealing units, but in an “INDIRECT” way, through a terminal box with type of protection “increased safety” (Ex “e”), dispensing with the need for additional field installation of Ex “d” type installation components and accessories.
Example of “Ex” equipment installation with metallic “explosion-proof” type enclosure, showing detail of INDIRECT cable entry system through factory-sealed cable(bushings) of the “explosion-proof” type (Ex “db”) and cables for connection to terminal strips in “increased safety” junction box (Ex “eb”)
Example of “Ex” LED luminaire installation with “explosion-proof” type metallic enclosure, showing detail of INDIRECT cable entry system through sealed (bushing) of “explosion-proof” type (Ex “db”) and cables connected to terminal blocks in “increased safety” junction box (Ex “eb”). Complete “Ex” equipment markings: Ex db eb IIC T4 Gb / Ex tb IIIC T135ºC Db
Example of “Ex” equipment installation incorporating the combination of Ex “db” and Ex “eb” protection types, comprising metallic Ex “db” explosion-proof enclosure (internally containing sparking components) and “increased safety” type terminal box (Ex “eb”), in the lower part, with an INDIRECT cable entry system through sealed cable bushings. Complete “Ex” equipment certified for installation in explosive atmospheres, with markings Ex db eb IIC T5 Gb / Ex tb IIIC T100ºC Db
Example of installation (on the left side) of “Ex” equipment incorporating the combination of Ex “db” and Ex “eb” protection types, consisting of metal Ex “db” explosion-proof enclosure (internally containing sparking components) and of “increased safety” type terminal box (Ex “eb”), with system of INDIRECT cable entries through sealed (bushings). On the right side can be seen power circuit distribution panels, with plastic enclosures, internally containing individually certified (Ex db eb IIC Gb U) spark gaps (circuit breakers and contactors). Complete “Ex” equipment certified for installation in explosive atmospheres, with markings Ex db eb IIC T4 Gb / Ex tb IIIC T135ºC Db
Example of an “Ex” equipment installation incorporating the combination of Ex “db” and Ex “eb” protection types, consisting of Ex “db” explosion-proof metallic enclosure (internally containing sparking components) and “increased safety” type terminal box (Ex “eb”), installed in the lower part, with an INDIRECT cable entry system through sealed cable (bushings). On the cover of the Ex “e” terminal box can be seen the installation of individually certified (Ex db eb IIC Gb U) spark gaps (control buttons, signalers and “Ex” measuring instruments). Complete “Ex” equipment, certified for installation in explosive atmospheres, with markings Ex db eb IIC T4 Gb / Ex tb IIIC T135ºC Db.
Roberval Bulgarelli
Technical Consultant on equipment and facilities in explosive atmospheres Electrical Engineer, with Master’s degree in protection of power electrical systems (POLI/USP) Book Organizer of the “The total life cycle of facilities in explosive atmospheres”