Class 1 Division 2 seal of requirments as related to explosion proof enclosures

[Vance G]

I have a 30amp explosion proof disconnect (enclosure) for my class1 division 2 HVAC equipment. The HVAC equipment has a sealed off explosion proof enclosure that contains all the spark causing components. There is less than 18" between the (2) enclosures. I have always chosen to error on the side of safety and use a seal off at both enclosures. But I have been told by our Electrical manager (I'm an HVAC manager) that it is allowable to use the single seal off at the HVAC and run 16" of seal tite to the top of the 30amp disconnect. I have nothing but 25 years of industrial HVAC experience and what I think is an accurate understanding of NFPA 496. Would someone please help me put this to rest once in for all? I need a clear conscience so I can ship this building.
Thanks in advace for anyones help,
Vance

 

[rbalex]

Being familiar with NFPA 496 is fine but it doesn?t appear to apply in this case. Familiarity with NEC Sections 501.15(A) & (B) would seem to be more useful.

Your colleague appears to be referring to Subsection 501.15(A)(3). While this is actually a Division 1 reference, it would also apply in Division 2. See the cross reference to 501.15(A)(3) in Subsection 501.15(B)(1); however, also note the phrase that all wiring methods between the seals in this application must be suitable for Division 1 wiring methods by the reference to 501.10(A).

In other words, one seal may be acceptable but ?seal-tite? would not be in this particular application.

 

[Vance G]

Thank you for your response. My "colleagues" did not accept your answer nor the fact that I used this source to confirm my opinion. So maybe I should rephrase it and you can dumb it down for them/me. At any time can you attach seal tite connectors, flexible conduit directly to the explosion proof enclosure in a class 1 division 2 area? This is an exterior installation in a refinery by the way.
Your expertise is valued by me I assure you.
Vance

 

[rbalex]

After reading my original answer, I see I should have proofread it a bit better. It should have said ??also note the phrase that all wiring methods between the seal and the enclosures in this application must be suitable for Division 1??

Essentially, everything between an explosionproof enclosure and its associated seal must be a wiring method suitable for Division 1; beyond the seal wiring methods suitable for Division 2 are acceptable; i.e., then LFMC may be appropriate. However, then be careful to observe Section 501.30. Especially review 501.30 (B) and note FMC and LFMC are not recognized as equipment grounding conductors for 30A circuits.

You can see my ?credentials? in my profile.

 

[Vance G]

Thank you sir. I never doubted you. I'm definitly grinning now that I read your profile and look forward to presenting this to those in doubt.
Have a great weekend,
Vance

 

[augie47]

Bob,
My question is by no means meant as a challenge. As you are no doubt already aware, my knowledge of Hazardous location wiring is woefully inadequate and I quickly admit I would not qualify as a pimple on your ***, but can you reference or explain the statement
"Essentially, everything between an explosionproof enclosure and its associated seal must be a wiring method suitable for Division 1" when the equipment is in a Class 1 Div 2 area (assuming I understood the OP).

 

[rbalex]

Bob,
My question is by no means meant as a challenge. As you are no doubt already aware, my knowledge of Hazardous location wiring is woefully inadequate and I quickly admit I would not qualify as a pimple on your ***, but can you reference or explain the statement
"Essentially, everything between an explosionproof enclosure and its associated seal must be a wiring method suitable for Division 1" when the equipment is in a Class 1 Div 2 area (assuming I understood the OP).

With respect to the OP:

1. The 30A disconnect and HVAC enclosure are required to be explosionproof. [Section 501.115(B)(1) – none of the alternates {501.115(B)(1)(1)-(4)} appear to apply to the HVAC unit]
2. In Division 2, Enclosures that are required to be explosionproof are also required to be sealed, essentially as if they were in Division 1 [Section 501.15(B)(1) with its cross references to 501.15(A)(1) and (3)] and everything between the enclosure and the seal must be consistent with Division 1 wiring methods [Section 501.15(B)(1) cross reference to 501.10(A)]

 

[augie47]

Thanks for the references. I will put my study hat on

 

[rbalex]

Thanks for the references. I will put my study hat on

Hazardous locations isn’t rocket science but it is a bit more than common sense. If it were only common sense, we probably wouldn’t worry about Divisions or Zones. In Class I, we would just build to Division 1 and not look back.

Think in terms of the fire triangle (fuel, oxidizing agent, ignition source) where oxygen (the most common oxidizing agent) will constantly be available.

In Division 1, fuel is also available often enough in “normal” operations so we attempt to protect against both common and uncommon sources of ignition. Division 1 is actually easy to design for; there are few options available. But it’s generally too expensive for overall use.

In Division 2, fuel is not commonly available so typically we only try to avoid common sources of ignition; i.e., arcs, sparks and high temperatures (ASH) that occur while the installation is behaving normally. It takes more knowledge and judgment to apply.

If you review the protection techniques in Section 500.7 and their scopes of protection you will see they generally attempt to deal with fuel or ignition sources or both. Note that explosionproof only deals with Class I. See the definition in Section 500.2

In Division 2, explosionproof equipment is not always required. But, unless some other protection technique is properly applied, it is required for any ASH components. In some cases, explosionproof equipment may be used, but not required.

Where explosionproof equipment is required in Division 2, seals are required to maintain the integrity of the enclosure. Also any wiring method between the enclosure and the seal must also be suitable to maintain the explosionproof integrity and only Division 1 wiring methods are suitable for that.

BTW for those that feel compelled to bring up Zones as an alternative, we wouldn’t even worry about them if “…we would just build to Division 1 and not look back.” Ultimately, the analysis would remain the same for flameproof unless you wanted to somehow only build for Zone 0.

 

[Vance G]

I thought I would let everyone know that we/I convinced the electrical team that it was necessary to install the seal off as discussed. Begrudingly, it has been installed properly.
I appreciate eveyones help and plan to have my company donate to your forum. I found it very informative and plan to use it in the future.
Have a great weekend,
Vance Gregory

 

[weressl]

Bob,
My question is by no means meant as a challenge. As you are no doubt already aware, my knowledge of Hazardous location wiring is woefully inadequate and I quickly admit I would not qualify as a pimple on your ***, but can you reference or explain the statement
"Essentially, everything between an explosionproof enclosure and its associated seal must be a wiring method suitable for Division 1" when the equipment is in a Class 1 Div 2 area (assuming I understood the OP).

The XP seal on an XP enclosure is to contain the internal explosion. So the connecting wiring method between those two also must be suitable to withstand and be part of the containment of the explosion. A piece of rigid conduit - for example - can fulfill that need, but not an FMC or LFMC.