IS Barrier Requirements

[kcca]

I have an application involving a Class 1 Div 2 Group C,D area. The primary PLC control system will be located in a non-hazardous control room in an enclosure. This enclosure will also contain the I/O modules. The I/O modules are AB Flex I/O and the supplier states that they are rated for Class 1 Div 2 locations. Although they have this rating, will IS Barriers be required to interface the Flex I/O modules with the field instruments that are located outside of the non-hazardous area and within the designated Class 1 Div 2 Group C, D area? Even though the I/O modules are rated for Class 1 Div 2, I believe that IS Barriers are still required.

 

[petersonra]

I have an application involving a Class 1 Div 2 Group C,D area. The primary PLC control system will be located in a non-hazardous control room in an enclosure. This enclosure will also contain the I/O modules. The I/O modules are AB Flex I/O and the supplier states that they are rated for Class 1 Div 2 locations. Although they have this rating, will IS Barriers be required to interface the Flex I/O modules with the field instruments that are located outside of the non-hazardous area and within the designated Class 1 Div 2 Group C, D area? Even though the I/O modules are rated for Class 1 Div 2, I believe that IS Barriers are still required.

It depends entirely on what the field devices that are located in the C1D2 area are.

The I/O modules can be located in a C1D2 area based on their listing, but the device(s) they are wired to might not be.

 

[don_resqcapt19]

I have never used an IS barrier for instruments in a Class I, Division 2 area. In general electronic instruments (that have no arcing contacts) are suitable for use in Class I, Div 2 areas without IS barriers or seals. Equipment with arcing contacts need explosion proof enclosures and seals or barriers.
What are the field devices that are to be installed?

 

[kcca]

I have never used an IS barrier for instruments in a Class I, Division 2 area. In general electronic instruments (that have no arcing contacts) are suitable for use in Class I, Div 2 areas without IS barriers or seals. Equipment with arcing contacts need explosion proof enclosures and seals or barriers.
What are the field devices that are to be installed?

Thanks to both of you for the quick reply. Regarding the location of the I/O modules, they will reside in a non-hazardous area within the central control room. Field wiring to the transmitters will be home runs to the central control room where the I/O modules are located.

The instruments are nothing special. They are basically 4-20 ma type analog inputs (i.e. PT's, FT's, LT's, etc.). These instruments will be located in the C1D2 area, and the twisted pair from each instrument will be home run back to the control room.

 

[weressl]

Thanks to both of you for the quick reply. Regarding the location of the I/O modules, they will reside in a non-hazardous area within the central control room. Field wiring to the transmitters will be home runs to the central control room where the I/O modules are located.

The instruments are nothing special. They are basically 4-20 ma type analog inputs (i.e. PT's, FT's, LT's, etc.). These instruments will be located in the C1D2 area, and the twisted pair from each instrument will be home run back to the control room.

In Div. 2 IS would be an overkill. I suggest that you investigate if your circuits meet the qualifications of a non-incendive circuit. To simplify it, non-incendive differs from IS mainly in the fault tolerance requirements, but is still concerns itself with the energy storing capability of the installed circuits. As long as your circuit produce neither excessive heat, or arcs - with sufficient energy to be the source of ignition - under normal operating conditions you may deem those circuits to be safe.

 

[Smart $]

... Although they have this rating, will IS Barriers be required to interface the Flex I/O modules with the field instruments that are located outside of the non-hazardous area and within the designated Class 1 Div 2 Group C, D area? Even though the I/O modules are rated for Class 1 Div 2, I believe that IS Barriers are still required.

IIRC, it is at least in part dependent on the chosen wiring method. Running your signal conductors/cable(s) in a C1D2-compliant conduit system does not require IS barriers. If you want to run open wiring (cables), you must use IS barriers. Some equipment must be certified for use in an IS system. Some may not need certified (e.g. thermocouples).

Click the link that follows for some more info:

http://www.omega.com/techref/intrinsic.html

 

[Smart $]

In Div. 2 IS would be an overkill. I suggest that you investigate if your circuits meet the qualifications of a non-incendive circuit. To simplify it, non-incendive differs from IS mainly in the fault tolerance requirements, but is still concerns itself with the energy storing capability of the installed circuits. As long as your circuit produce neither excessive heat, or arcs - with sufficient energy to be the source of ignition - under normal operating conditions you may deem those circuits to be safe.

I knew there was something else I was forgetting.

 

[weressl]

IIRC, it is at least in part dependent on the chosen wiring method. Running your signal conductors/cable(s) in a C1D2-compliant conduit system does not require IS barriers. If you want to run open wiring (cables), you must use IS barriers. Some equipment must be certified for use in an IS system. Some may not need certified (e.g. thermocouples).

Click the link that follows for some more info:

http://www.omega.com/techref/intrinsic.html

You can use cable tray or it's "Orphan Annie" derivative; wire basket in Div. 2 installation. I consider those 'open wiring'. Unsupported open wiring has further restrictions on the cable type and length of unsupported exposure, although the later is fairly ambigous for instrument circuits.

 

[petersonra]

most new 2 wire xmtrs are going to be OK for use in C1D2 areas. Note I wrote "most".

take a look at the specs for the xmtrs.