Seals on Cables in Tray from Non-Haz to Haz

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Kobe85

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New York
I'm working on a strange project - we are building a CNG compressor on a flatbed trailer. There are three areas on the trailer, the front of it is exposed to the atmosphere and is non-hazardous, the middle section is a compressor unit in an enclosure (C1D2), and back of the trailer which is exposed and contains more piping (C1D2).


I have one run required from the front of the trailer's MCC (non-hazardous) to the back of the trailer (C1D2); its a solo 480V run to a heater.

The first way, and not-preferable way, is to run conduit from the MCC to the enclosure wall of the compressor unit, seal it on outside, penetrate the wall with a myers bulkhead etc. and land the wires inside the enclosure in a small Crouse EAB junction box, then come out of that with cable and tray and run towards the back of the trailer out of the compressor wall.

Another simpler way, is to run cable tray from the MCC up over top of the Compressor Enclosure and towards the back of the trailer. The only issue is, how do I seal this cable from the hazardous to non-hazardous atmosphere? It does not seem to fall under any of the circumstances in the NEC. What you might ask is what cable am I using, well, I'm using a non gas/vapor tight cable - which is probably the root of all my problems. But we never purchase type MI or vaportight cable and I'm still not even sure that would get me through this scenario.

Any ideas?
 

rbalex

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  1. How do you know the cable doesn't have a "gas/vaportight continuous sheath"? Type MI isn't your only option and anything acceptable in cable tray probably has a gas/vaportight continuous sheath. Type TC definitely does.
  2. If the back of the truck only has closed piping, it may not necessarily need to be classified.
  3. The compressor enclosure however, may need to be Division 1. It depends on ventilation.
  4. Penetrating the wall with a Myers hub puts a fitting between the seal and the boundary - a violation.
 

Kobe85

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New York
  1. How do you know the cable doesn't have a "gas/vaportight continuous sheath"? Type MI isn't your only option and anything acceptable in cable tray probably has a gas/vaportight continuous sheath. Type TC definitely does.
  2. If the back of the truck only has closed piping, it may not necessarily need to be classified.
  3. The compressor enclosure however, may need to be Division 1. It depends on ventilation.
  4. Penetrating the wall with a Myers hub puts a fitting between the seal and the boundary - a violation.

Thanks for the reply. What confuses me is that I could have this myers hub just inside the enclosure (which is not XP) and it would be acceptable, but since it straddles the wall and pokes just outside the enclosure it isn't acceptable.

For this application we are wiring this conduit on the outside of the enclosure, but in the past we have just provided the compressor enclosure to our customers with a myers bulkhead on the outside so they can connect their conduit to it; and there haven't been any issues onsite with AHJ. For what its worth, this bulkhead is a gateway through flex conduit to our control panel (including NI wiring), so they can wire their 120V etc signals from the MCC and DCS.
 

rbalex

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The basic sealing rule for Class I, Division 2/unclassified boundaries [Section 501.15(B)(2)] is no threads except those inherent to the seal or a reducer at the seal are permitted between the seal and the boundary. Threads provide a pathway for gases to be transmitted between the Division 2 and unclassified locations. Seals themselves aren't perfect and are used only to "minimize" the transition of gases and vapors. [Section 501.15 FPN/IN No. 1]

The truth is, most of the time, no boundary seals are needed at all as evidenced by the many Exceptions to Section 501.15(B)(2) and the fact that, even where they are required, they aren't required to be explosionproof. Of course, there aren't supposed to be any gases/vapors in Division 2 locations to transmit under design operating conditions in the first place.

Nevertheless, a Myers hub is prohibited at the boundary.

I'm still concerned about the enclosure, whether limited to the compressor or overall. Standard classification practices would indicate that the interior would be Division 1. The fact that no problems seem to have occurred is probably that the interior still uses Division 2 wiring methods. In a stable environment, Division 2 wiring methods would probably "work" most of the time. By "stable enviornment", l mean nothing inherently attacks the equipment or wiring methods by mechanical or chemical means.
 

Kobe85

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Location
New York
rbalex, sorry for not being clear on the enclosure. This enclosure has a large cooling fan (nearly 6 feet wide) and louvers on the side for ventilation. There is no build up of gas causing a C1D1 environment. The enclosure itself is approx 10' x 14'

In regards to the penetration on the enclosure wall, I'm still not sure of the best way to do it; do you have a suggested way? We can't put the seals on the inside since it would cause a manufacturing nightmare.

What if we put a crouse-hinds sealtite (LFMC) fitting with male threads through the enclosure wall, and the seal could connect directly to it from the outside. Do you think this is acceptable?
 

rbalex

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Have you abandoned your cable tray option from your first post? Several multiconductor cable types such as TC, PLTC, ITC, etc., do not require boundary seals even if they aren't sealed at the terminations. [Section 501.15 (E)(3)] This is easier to see in the 2011 NEC than the 2014 where you have to parse Section 501.15 (E)(1) carefully as well as Section 501.15 (E)(3) to get the whole story. My understanding is ISA has a PI/PC to make it clear again in 2017.

If you are concerned with the bulkhead penetrations, you could still use a cable tray system. You could use various tray cable bulkhead sealing walls without raceways at all OR you could simply leave the opening unsealed. In either case - still no boundary seals are required. There is a slight penalty if the penetration is left open. A 3' Division 2 envelope will extend from the opening. BTW this applies to the louvres as well.
 

iwire

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Location
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Any reason not to simply run conduit out of the bottom of the MCC under the trailer bed and back up through the deck at the back end?

We wired a large machine on a trailer with MCC at the front and did that with a number of runs.

But there were no hazardous locations so I don't know if that changes things.
 

Kobe85

Member
Location
New York
Have you abandoned your cable tray option from your first post? Several multiconductor cable types such as TC, PLTC, ITC, etc., do not require boundary seals even if they aren't sealed at the terminations. [Section 501.15 (E)(3)] This is easier to see in the 2011 NEC than the 2014 where you have to parse Section 501.15 (E)(1) carefully as well as Section 501.15 (E)(3) to get the whole story. My understanding is ISA has a PI/PC to make it clear again in 2017.

If you are concerned with the bulkhead penetrations, you could still use a cable tray system. You could use various tray cable bulkhead sealing walls without raceways at all OR you could simply leave the opening unsealed. In either case - still no boundary seals are required. There is a slight penalty if the penetration is left open. A 3' Division 2 envelope will extend from the opening. BTW this applies to the louvres as well.

I haven't decided yet, and I looked into that and do like the PLTC option which we are using throughout, didn't know they were considered gas-tight; thank you for that. One nice thing about the conduit was we were using a bunch of THHN wires, which if in a cable would need to be a much larger multi-conductor that I'm not sure I will be able to find in time. Where in the code does it mention the penetration and envelope extension?

Only concern is, a lot of the time we only supply the compressor & enclosure and our customer connects to those bulkheads with their field conduit, so I'm not sure what the best option is there.
 

Kobe85

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Location
New York
Any reason not to simply run conduit out of the bottom of the MCC under the trailer bed and back up through the deck at the back end?

We wired a large machine on a trailer with MCC at the front and did that with a number of runs.

But there were no hazardous locations so I don't know if that changes things.

we have considered wiring beneath like you mentioned; unfortunately the boundaries and sealing still are tough figure out with conduit in this scenario, maybe even more difficult.
 

rbalex

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... Where in the code does it mention the penetration and envelope extension?...
First memorize, "This Code is not intended as a design specification or an instruction manual for untrained persons." Section 90.1(A) or (C) depending on the edition.

Second read Section 500.4(B) for the myriad reference standards that may apply. Except for applications covered by Articles 511 to 516, the NEC doesn't actually indicate how to classify a location.

Type TC has several multiconductor cables available. Many effectively use THHN and Type TC-EL can run "open" for up to 6'.

Conduit will always present a boundary problem unless one of the Exceptions to 501.15(B)(2) applies. However, Division 2/unclassified boundary seals aren't required to be explosionproof.
 

Kobe85

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Location
New York
rb,

I guess the best option is maybe to go with type TC cable in cable tray beginning in the non-haz area from the MCC. A water-tight gland on the compressor enclosure (C1D2) housing at the cable entry and then the cable would run to the control panel inside of the enclosure.

The compressor enclosure housing is not XP, so according to 501.15(E)(1 to 4) using type TC (gas tight) cable I don't even need a cable seal.

I guess what makes me nervous is the enclosure is still the boundary between C1D2 and non-haz, but this section on cable seals doesn't require it.
 

rbalex

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...
The compressor enclosure housing is not [required to be] XP, so according to 501.15(E)(1 to 4) using type TC (gas tight) cable I don't even need a cable seal.
...
You best hope Section 501.15(E)(4) doesn't apply; it's the only case where a boundary seal is required - and it's a nightmare to achieve. (Thankfully, it doesn't apply :D) FWIW, 501.15(E)(2) doesn't apply either. Only Type MI is covered and it has its own installation requirements anyway.

Otherwise, I can pretty well endorse your design as I understand it.

As an afterthought, where can you (or I) show Type TC has a "gas/vaportight continuous sheath"?
 

Kobe85

Member
Location
New York
You best hope Section 501.15(E)(4) doesn't apply; it's the only case where a boundary seal is required - and it's a nightmare to achieve. (Thankfully, it doesn't apply :D) FWIW, 501.15(E)(2) doesn't apply either. Only Type MI is covered and it has its own installation requirements anyway.

Otherwise, I can pretty well endorse your design as I understand it.

As an afterthought, where can you (or I) show Type TC has a "gas/vaportight continuous sheath"?

The UL whitebook!
 

Kobe85

Member
Location
New York
an issue that the NEC does not seem to address:

The cable run from the MCC (non-haz area) to the compressor enclosure (C1D2) will have a liquid-tight connector on the compressor enclosure, before terminating at a control panel inside with another connector. Will this entry between the hazardous and non-hazardous barrier extend the C1D2 hazard into the non-hazardous area? So maybe here I need a C1D1 gland with a barrier?

There will be motors, estop switches, and of course the MCC within a few feet or ten feet of this penetration in the non-hazardous area.

This scenario does not seem to be in the seals required section.
 

nhee2

Senior Member
Location
NH
Are you sure the compressor enclosure is a haz area boundary? NFPA 52 would say that 15' from compression equipment is classified Div 2.
 
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