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|
Increased safety (Ex e)
|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
|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.
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.
Use the FieldConnex® product selector to see illustrations of all installation methods with and without ignition protection as well as appropriate products.