Thermocouples in Class 1 Div II Equipment

[GoldDigger]

Do all of those devices have direct inputs for TC wire or are there temperature transducers you are not mentioning?
And if direct inputs, what assurance do you have that a fault in, for example, the data logger would not apply a dangerous current or voltage to the TC leads?
A simple apparatus is not necessarily safe if connected to an unspecified non-IS power source.


Tapatalk!

 

[fifty60]

They all accept T/C inputs directly. outside of the safety barriers, which do not come standard, there would not be any extra protection.

If I add the barriers for extra protection, do I necessarily have to go the whole 9 yards for the IS labeling found in NEC 504, or can I just add the barriers as an extra precaution?

Do I have to do a "fault analysis" in order to determine whether or not a Thermocouple is a simple apparatus? Or, per the definition, can I proceed as if it were a simple apparatus?

 

[fifty60]

Since my goal is Class 1 Division 2 and not an Intrinsically Safe Circuit, would it be appropriate to treat the thermocouples as Nonincendive Field Wiring and run them normally? They are definitely ran as separate cables as required in 501.10(B)(3).

Adding ISB's to non-incendive field wiring is not required, but it should not change the fact that it is non incendive field wiring right?

I normally seal the entry point of the thermocouples with silicone. Using 501.15(E)(4) "Cables without Gas/Vaportight Sheath" would I be permitted to silicone entry point of the T/C into the Class 1 Div 2 location? No other sealed fittings required? Would ther be any problem with this? Or would I have to run the t/c through a conduit and use sealed fittings?

 

[fifty60]

Not sure why I struggle so much with the concept of "Control Drawing", but will I end up with several control drawings for each separate electrical component inside of my hazardous area? Should I be able to obtain a control drawing for thermocouples?

 

[rbalex]

Not sure why I struggle so much with the concept of "Control Drawing", but will I end up with several control drawings for each separate electrical component inside of my hazardous area? Should I be able to obtain a control drawing for thermocouples?

From what you have described so far, you don't need a control drawing and you don't need either an IS or NI system.

Section 501.15(E)(4) requires a boundary seal. VERY painful, especially if installed in a raceway. Every wiring method in Section 501.10(B)(3)-(5) will meet 501.15(E)(3). You won't need seals unless required by 501.15(E)(1) and there the cable type is irrelevant.

 

[fifty60]

Thanks or the explanation. The cables in this installation will be thermocouples. Is it correct to look at them as cables? Or, do you mean that since the t/c's in this installation do not need to be NI or IS, that all I have to worry about are the boundary seals. Sorry, do not have my NEC Handbook in front of me at the moment, will have to take another look at it in the morning.

 

[rbalex]

If they are jacketed they are multiconductor cables, probably PLTC or ITC rated or both and subject to 501.15(E)(3). If there is no overall jacket, then they are simple conductors in conduit and subject to 501.15(B)(2).

 

[fifty60]

Looking at 501.15(E)(3), it states "unless the cable is attached to process equipment or devices". Can someone please give me an example of a cable connected to process equipment or devices? Some of the T/C's are connected directly to sheath heaters, others are t/c probes directly in the air stream.

There is one T/C that is connected to a temperature limit controller in the safe zone. The process end of the T/C that is located in the hazardous area is a ring and is intended to be attached to whatever the customer intends to put in the hazardous area. Would this be considered a "cable connected to process equipment"?

Also, there are 8 separate ring thermocouples that are available to the customer for the same exact thing. They can connect them to anything they put inside of the hazardous area. Would these be considered cables connected to process equipment?

I understand that the T/C can be classified as non incendive, but do the controllers they are attatched to also have to be considered non incendive as well? Some of the PID's are powered from 120VAC, the T/C's attatched to these will be ran through an isolation barrier before entering the hazardous area. The 8 thermocouple data acquisition input module is powered from a 24VDC class two power supply. Would this module (or power supply) have to have a specific rating to be able to proceed with the non incendive wiring approach laid out in 501.10(3)?

Is the reason I do not need IS or NI the fact that I only have thermocouple inside of the hazardous area? These are not considered equipment, so only wiring practices are relevant in this situation?

 

[fifty60]

The 24VDC power supply that supplies the 8 T/C input data logger is UL1604 listed. Will the actual data logger need to be UL1604 as well, or would it suffice that the power supply is UL1604?

 

[fifty60]

What is meant by "process equipment"? Would the sheath heaters be the process equipment, since they are used to raise the temperature in the C1D2 area?

 

[fifty60]

The T/C's do have jacketing around them, so I would classify them as cables. The T/C's are not a continuous sheath imho, because the cable is broken at the end of the cable because a ring is attatched so that it can be fastened to a surface/object inside of the hazardous area. I believe that 501.15(E)(4) would apply.

(E)(4) does not specify the sealing method that should be used. Would silocone at the entry point of the T/C's from the non classified to classified suffice as it "minimizes the passage of gases or vapors"?

 

[fifty60]

I believe the ring t/c's fall under the 501.15(E)(4) "Cables capable of transmitting gases or vapors".

 

[fifty60]

Thermocouples are "non-incendive field wiring". Non-incendive field wiring needs to be installed according to the control drawings. Thermocouples do not need a control drawing. I can install the thermocouples using any unclassified wiring method, and I do not need a control drawing.


Anyone disagree with this interpretation?

I do not want to peel the jacket back on these thermocouples and seal them at the barrier between classified/unclassified area. I do not feel that it is needed. 501.10(B)(3) seems to be the only clause that allows this depending on the above interpretation being valid.

 

[Smart $]

...
I do not want to peel the jacket back on these thermocouples and seal them at the barrier between classified/unclassified area. I do not feel that it is needed. 501.10(B)(3) seems to be the only clause that allows this depending on the above interpretation being valid.

IMO, if you enter the boundary with conduit, you need a conduit seal no matter what the contained wiring method is.

And as I understand it, the T/C cables are exposed to the hazardous location environment after entry, so you'll also need cable seals unless the cables qualify under the condition of 501.15(E)(2).

 

[fifty60]

For a C1D1 location, I would have to peel the jacket all the way back to the boundary of the hazardous/non hazardous locations. C1D2 does not explicitly say to peel back the jacket, but 501.15(E)(4) does say "sealed at the boundary of the division 2 and unclassified location in such a manner as to minimize the passage of gases or bapor into an unclassified location"

What options do I have besides peeling the jacket all the way back? There is about 6 feet of T/C wire fore each T/C wire inside the hazardous area. I have 8 T/C's in all, each around 6 feet in length. Am I able to break the jacket at the boundary and seal there? Or should I peel back from the tip to the boundary?

Would I have a problem using 501.15(E)(3) for a t/c with a ring attatched, or a T/C with a probe attatched? How about a T/C without a ring or probe? The T/C cable itself fits 501.15(E)(3), but I am not sure how to handle the tip of the T/C, whether it be stranded, ringed, or a probe.

 

[rbalex]

...

And as I understand it, the T/C cables are exposed to the hazardous location environment after entry, so you'll also need cable seals unless the cables qualify under the condition of 501.15(E)(2).

Reread 501.15(E)(3) carefully:

501.15(E)(3) Cables Capable of Transmitting Gases or Vapors. Cables with a gas/vaportight continuous sheath capable of transmitting gases or vapors through the cable core shall not be required to be sealed except as required in 501.15(E)(1), unless the cable is attached to process equipment or devices that may cause a pressure in excess of 1500 pascals (6 in. of water) to be exerted at a cable end, in which case a seal, barrier, or other means shall be provided to prevent migration of flammables into an unclassified location.
[underlines and bolt "not" mine.

Section 501.15(E)(2) basically applies to MI cable. UL certifies TC, ITC, PLTC, corrugated armor MC and some MV cables to meet 501.15(E)(3). Section 501.15(E)(4) applies basically to MC cables with interlocked metal tape armor - even with an overall nonmetal jacket.

The clause "... unless the cable is attached to process equipment or devices that may cause a pressure in excess of 1500 pascals (6 in. of water) to be exerted at a cable end..." is covered by Section 501.17. In fact, it has been for several Code cycles; just not as clearly. [I have a new Public Input for 2017 ]

You are correct that conduit seals are still required at the boundary. Cable seals are also required at the boundary for Section 501.15(E)(4) cables. Which is what I said in Post #25. Section 501.15(E)(3) cables, may be considered single conductors in conduit at the boundary.

 

[fifty60]

For these thermocouples there normally is not conduit. They run through the equipment and then enter the hazardous area through the wall. Then red silicon is applied to the entry point as a seal.


Looking at 501.15(E)(3) Cables Capable of Transmitting Gases or Vapors. Cables with a gas/vaportight continuous sheath capable of transmitting gases or vapors through the cable core shall not be required to be sealed except as required in 501.15(E)(1)...

Ok, so the t/c cable is a continuous sheath (the jacket=sheath) and it is capable of transmitting gases or vapors through the cable core because the end of the cable is terminated into a ring, or probe, or just the stranded ends. I then reference 501.15(E)(1) and see that it only applies to "explosion proof". Since I am not required to be "explosion proof", I do not have to peal the t/c jacket back to the boundary and seal it at the boundary.

Also, since I only have the T/C in the C1D2 area, the process seal requirement in 501.15(E)(3) does not apply.

Does this seem like a valid interpretation?

 

[Smart $]

Reread 501.15(E)(3) carefully...

I did. A not-bolded "not" is not in my 2014.

fifty60 has said continuous sheath. For 501.15(E)(3) to apply, the continuous sheath must be of a gas/vaportight material. I'm not absolutely certain of what materials that includes, but I've always considered it to mean a metal-tube jacket... not an interlocked, spiral-wrapped, metal-ribbon jacket or any other non-metallic jacket.

 

[rbalex]

I did. A not-bolded "not" is not in my 2014.

fifty60 has said continuous sheath. For 501.15(E)(3) to apply, the continuous sheath must be of a gas/vaportight material. I'm not absolutely certain of what materials that includes, but I've always considered it to mean a metal-tube jacket... not an interlocked, spiral-wrapped, metal-ribbon jacket or any other non-metallic jacket.

Ok, I cited 2011, but the content was only reworded. It still only requires sealing such cables at enclosures required to be explosionproof or process connections. [501.17] Otherwise, I don't believe Users would have let the Proposal stand; they only need one other vote to veto.

edit add: Check the UL White Book for gas/vaportight cables certifications.

 

[rbalex]

From the UL White Book

POWER AND CONTROL TRAY
CABLE (QPOR)
...
Regarding cable seals outlined in Article 501 of the NEC, Type TC cable has a sheath which is considered to be gas/vapor tight but the cable has not been investigated for transmission of gases or vapors through its core.

This is the last sentence under "PRODUCT MARKINGS". Several other cable types have similar statements.