Myers hub with TMCX fittings Class 1 Division 2 for NEMA 4 Junction box

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We beginning to plan a project in Class 1 Division 2 area. It will have a NEMA4 junction box with just terminal blocks and the field devices mounted on the skid will terminate here. The customer will connect their control wires at the junction box and run it back to their PLC. I have a couple of field devices that will need seals. Base on the construction of the skid I will like to use a MC cable rated for the area. I would like to use TMCX fittings (rated Class 1 Div. 1) on both ends of the MC cable (and seal the ends). I need to terminate the TMCX fittings to the NEMA 4 junction box and would like to use Myers hubs. The compliances on the Myers hub is rated for Class 1 Division 2. My question is will all the parts be in compliances and fit all together? Thanks in advance for you comments.
 

rbalex

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Without reviewing the shop drawings, I can only make a few preliminary comments:

Myers hubs are usually fine in Division 2 but make sure they are also specifically rated as grounding devices.

The TMCX fittings are also fine but you only need to seal the Type MC cables at the ends where they enter enclosures that are also required to be sealed. Sealing at the Type 4 box is probably unnecessary.
 
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I have a few more questions:
Without reviewing the shop drawings, I can only make a few preliminary comments:

I also checked the spec and the ratings of both the Myers Hub and the TMCX fittings and it look like both are compatible together.

Myers hubs are usually fine in Division 2 but make sure they are also specifically rated as grounding devices.

The Cooper Myers hub , Basic Scru-Tite (example ST1), is listed as electrical ground as per their spec sheets. Now,there is also the Ground Hub (example STG) with a grounding screw. Both are UL Listed. My question both are listed as a grounding hub, but the STG has the ground screw. Would the STG be a better choice as it has a visible ground connection? If I use it what would the best way to run a ground wire to the hub? A single ground wire daisy chained to each hub or a individual ground wire ran to each individual hub and then back to a ground bar?


The TMCX fittings are also fine but you only need to seal the Type MC cables at the ends where they enter enclosures that are also required to be sealed. Sealing at the Type 4 box is probably unnecessary.

The MC cable with TMCX fittings will be sealed at the field devices. Would it be too much if the MC cable is sealed at the junction box end, if the TMCX fittings are used there also?
Thank you for your comments.
 

rbalex

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A Myers hub/TMCX (or TMC) interface is no problem.

My oversight. I should have referenced Section 501.30(A). The actual issue is bonding. The basic ST1 is fine in unclassified locations; however it essentially uses a "locknut/bushing" type bond and is unacceptable in classified locations. The STG should be used.

The TMCX is overkill where a seal is not needed; a TMC/STG is suitable at the junction box.
 
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I see a lot of that here in the Bakken. And lots of confusion about it as well. As Mr Alexander mentioned, the Myers hubs with grounding are acceptable in Class I Division 2 areas. As for sealing the MC or MC-HL cables leaving the Nema 4 box, that will depend where the box is located and where the cables are going. As you mentioned, some of your devices needed sealing for their Explosionproof ratings. Devices that are listed and labeled Non-Incendive or Factory Sealed and switches that are listed and labeled as hermetically sealed probably would not need TMCX fittings and could use the less expensive TMC fittings. Likewise MC/MC-HL cables going from one non-explosionproof enclosure to another in the same Class I Division 2 area on the skid would not need TMCX fittings unless the enclosure itself needed to be sealed. IF the Nema JB in question is located in a hazardous location and the PLC is in another remote location, the MC/MC-HL cables would need a TMCX at one end (preferably the hazardous area end) to serve as a boundary seal. The other end would only need a TMC fitting. Now if at some point, you use MC-HL cable in a Class I Division 1 area, then both ends would need TMCX fittings.
 

rbalex

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... IF the Nema JB in question is located in a hazardous location and the PLC is in another remote location, the MC/MC-HL cables would need a TMCX at one end (preferably the hazardous area end) to serve as a boundary seal ...
This is incorrect; no boundary seal is required. See Section 501.15(E)(3).
 
To Robert RE 501.15 (E)(3)

To Robert RE 501.15 (E)(3)

OK, I am confused a bit then. Can you give me some further clarification?

501.15 (E)(3) says that cables with a continuous vapor tight sheath capable of transmitting gases or vapors shall be sealed as per 501.15 (E)(1). which for Class I Division 2 then get me to a listed sealing fitting that will seal the cable and conductors. Since a multi-conductor MC-HL cable can transmit vapor inside the MC sheath, this leads me to install a boundary seal when leaving the area just as I would if I was running RMC to the control room. Here in the Bakken fields, much of the facilities are build with modular skids (buildings). This lets the the actual site facilities to be constructed quickly as soon as the drigging rigs move off. Most of these skids are Hazardous locations and many are Class I Division 2 only because API 500 allows them to be declassed a level with gas detection. Interconncet cabling is often MC or MC-HL. The main facilitiy PLC is often located inside the Electrical Modules which are one of the few General Purpose areas in the facilities. So we get power, control and communications cables that have the capability of transmitting vapor between hazardous and general purpose locations. Some modules have pressureized piping and in North Dakota the wind can be significant. Thus a potential to develop a driving pressure differential between modules as well. In my pipeline days we always ran RMC. If I were using RMC here instead of MC-HL i would certainly need boundary seals between the hazardous modules and the EM. While MC-HL would not transmit vapor as easily as RMC, I don't see where 501.15 (E)(3) permits me to not seal the cable between the hazardous and non-hazardous areas.


So what am I miss interpreting?

Thanks
 

rbalex

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Well, that wasn't quite the question you originally asked in the PM. BUT this is what 501.15(E)(3) says:

(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.
I have emphasized what you appear to have missed.

In Class I, Division 2, cables installed under Section 501.15(E)(3) aren't required to be sealed at all unless they are already required to be sealed by Section 501.15(E)(1) because it was an enclosure that was also required to be explosionproof (and sealed) OR they are "... attached to process equipment or devices that may cause a pressure in excess of 1500 pascals..."

CMP14 has been doing its best to eliminate Division 2/unclassified boundary seals - they aren't even required to be explosionproof when they are required for raceways.
 

rbalex

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Hmm.... That's not how it reads in my 2014 NEC handbook. I'll have to find me a normal copy of NEC 2014 and check out what IT says...

Thanks
That's definitely "Hmm..." worthy and a great example of unintended consequences. (Also check the 2011 NEC and earlier editions)

Neither the 2013 ROP nor the 2013 ROC mentioned there was actually a need to require boundary seals for 501.15(E)(3) cables. The entire Section 501.15 went through a rewrite at the Technical Correlating Committee's direction but without public comment between the ROP and ROC. The rewrite's substantiation doesn't appear to justify cable boundary seals for Division 2/unclassified; Other Proposals just wanted to clarify that seals for Section 501.15(E)(1) weren't required to be conduit seals; i.e., it was simply:

Substantiation: This is a direction from the National Electrical Code Technical Correlating Committee in accordance with 3.4.2 and 3.4.3 of the Regulations Governing Committee Projects.
In the 2014 NEC still looks like 501(E)(1) only requires a seal where the enclosure is required to be sealed. "Cables entering enclosures that are required to be explosionproof shall be sealed at the point of entrance. The sealing fitting shall comply with 501.15(B)(1) or be explosionproof" (This is when a seal is required) The rest of the Section tells you how.

It looks like I have a "Public Input" for the 2017 NEC.
 
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