RTD and Transmitter Wiring

[epillow]

I need to wire RTD's and 4-20mA transmitters that are located in a C1D2 location to a control panel that is located in a C1D2 location. I would like to run multiple Tray Cables in a single conduit out of the enclosure and branch off to each sensor with the TC when I'm within a few feet of the sensor. My question is on the bonding. For a typical RTD I would need 3 conductors plus the shield. I want to connect the shield at only one termination, therefore, it will not act as a bond. So does that mean that I need to go with 4 conductor + shield and use one of the conductors as my bonding conductor? I also thought about running to the sensor using LFMC and including a THHN bonding conductor with the TC inside the LFMC. If I do that will I not need to install a bonding jumper in parallel with the LFMC?

Thanks

 

[petersonra]

I need to wire RTD's and 4-20mA transmitters that are located in a C1D2 location to a control panel that is located in a C1D2 location. I would like to run multiple Tray Cables in a single conduit out of the enclosure and branch off to each sensor with the TC when I'm within a few feet of the sensor. My question is on the bonding. For a typical RTD I would need 3 conductors plus the shield. I want to connect the shield at only one termination, therefore, it will not act as a bond. So does that mean that I need to go with 4 conductor + shield and use one of the conductors as my bonding conductor? I also thought about running to the sensor using LFMC and including a THHN bonding conductor with the TC inside the LFMC. If I do that will I not need to install a bonding jumper in parallel with the LFMC?

Thanks

does such wiring actually require an egc?

generally, you have to run the egc with the other conductors,so if you need one, IMO it has to be part of the tray cable.

 

[jatrottpe]

For the RTD's install Twisted/Shielded Triads wire size per specs (typically 18ga or 20ga (for multi triad cable use Twisted Shielded with overall shield)

For analog or discreet signals use Twisted/Shielded pair wire size per specs (typically 18ga or 20ga (for multi pair cable use Twisted Shielded with overall shield).

A seperate EGC wire within the instrument cable is typically not required. Make sure the conduit system, tray system, jboxes are bonded together.

Most instrument DCS systems want a clean signal reference and do not want ground noises induced onto their signals.

 

[megloff11x]

Is your RTD and its signal processor listed for the area? Hazloc is not easy or inexpensive since there are no hard and fast rules on seemingly innocuous but not listed items. Look at a C1D2 touch screen. Do you see USB ports or cable connections on the side exposed to the hazardous location? Hopefully no. Connecting and disconnecting even low Voltage items under power can cause a spark. You practically have to pay to list what you use if you can't buy listed items. The low Voltage and low current on the typical 100-ohm RTD would seem to be intrinsically safe, but you may have to prove it. What happens if the wire breaks and shorts - will it spark?

Try burying the signal processor in the cabinet outside the classified location as it will be more of an issue.

At least you're not Division 1.

Matt

 

[weressl]

I need to wire RTD's and 4-20mA transmitters that are located in a C1D2 location to a control panel that is located in a C1D2 location. I would like to run multiple Tray Cables in a single conduit out of the enclosure and branch off to each sensor with the TC when I'm within a few feet of the sensor. My question is on the bonding. For a typical RTD I would need 3 conductors plus the shield. I want to connect the shield at only one termination, therefore, it will not act as a bond. So does that mean that I need to go with 4 conductor + shield and use one of the conductors as my bonding conductor? I also thought about running to the sensor using LFMC and including a THHN bonding conductor with the TC inside the LFMC. If I do that will I not need to install a bonding jumper in parallel with the LFMC?

Thanks

Install equipment grounding to the panel unless the panel is already connected tot he ground by virtue of its mounting (directly bolted to a grounded steel structure). Unless you have operating voltages greater than 50V in the cabinet the grounding itslef would not serve a safety purpose. Only connect the shield and ground wire at one end, or one point to the ground. If you have multiple segments of a single loop, ex. device to junction box, JB to Control Room Terminal strip, CR strip to marshalling strip, marshalling strip to I/O, decide where will you have the SINGLE grounding point. You would most likely choose the CR strip, since this is the point where tha majority of the externally induced signals would end from the filed. Make sure the shield is landed ISOLATED at every oter points andconnected to each other from both sides. The instrument end and the I/O ends of the shielding/drain should be isolated and taped to insulate.

 

[bobgorno]

So does that mean that I need to go with 4 conductor + shield and use one of the conductors as my bonding conductor? I also thought about running to the sensor using LFMC and including a THHN bonding conductor with the TC inside the LFMC. If I do that will I not need to install a bonding jumper in parallel with the LFMC?

I would say go with the 4-conductor, shielded, phase tape one conductor green for the EGC, if you are trying to connect to your RTD using direct connect cable installation method. The cable must be TC, PLTC or ITC. If connecting with LFMC using fittings that are listed and approved for grounding, then your raceway is your EGC and no separate EGC is required.

The RTD connection head must be suitable for the area. The RTD must be suitable. See 501.15(F)(3). Your dual boundary would be the thermowell and the RTD sheath. Direct insertion of the RTD into the process would not meet the intent of 501.15(F)(3).

Bob

 

[epillow]

Thanks for all the replies, but... I'm really confused now. I've decided to go with the tray cable. Ordinarily I would use a twisted shielded pair for a transmitter and connect the shield at the controller only. I just don?t know if a EGC is required within the tray cable for a C1D2 installation. All of my components are listed C1D2 so that?s not an issue. So? do I need the EGC??