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Fieldbus in Hazardous Areas

Methods of ignition protection

Fieldbus in hazardous areas requires an infrastructure with suitable ignition protection. The table below shows the major protection methods.  Each method can be chosen for the segment as a whole, or for parts of the segment, i.e. the trunk or the spurs.


Protection Ignition Protection Applied in Attributes
Mechanical

Increased safety (Ex e)
Non-sparking (Ex nA)
Flameproof enclosure (Ex d) *)

Zones Protects against unintentional opening circuit. The same as for any electrical installation, such as lighting fixtures, motors, etc.
Enables long cable runs and high device counts
Explosion proof
Non-incendive wiring
Divisions
Electrical Intrinsic safety (Ex i) Zones and Divisions Hot work permitted.
For shorter cable runs.
For any hazardous area

*) Although this is not necessary with FieldConnex® components, on occasion a flameproof enclosure is applied for fieldbus junction boxes.


Where standard operation procedures require a hot work permit to be included with the work order, users often prefer mechanical methods of ignition protection.



Live maintenance on instruments

In order to enable work on instruments without a hot work permit, the spur and instrument connection must be installed intrinsically safe (Ex i) or with non-incendive field wiring. However, to fulfill demands for high device count and long cable runs, more power is required than is technically feasible with intrinsic safety.

The high-power trunk concept fulfills these demands. The trunk carries power to 31 V and 500 mA requiring a means of mechanical ignition protection similar to those of electrical lighting or motors. The device coupler is the intrinsic safety barrier installed in the fieldbus junction box near the instrument. Up to four device couplers per segment provide power and protection to the maximum number of 31 instruments as per the fieldbus standard.
 

Benefits:

  • Installation and maintenance crews benefit from working on field instrumentation without requiring a hot work permit during normal operation.
  • Engineers can utilize the maximum cable length permitted for fieldbus and a high device count per segment in any hazardous area.


This topology shows the most common installation methods for fieldbus. Mix and match of ignition protection methods on one segment is permitted.


Three steps to right product

Use the FieldConnex® product selector to see illustrations of all installation methods with and without ignition protection as well as appropriate products.