Conduit System Requirement for Class I, Division 2 - General Doubts 1

[trolex]

Hi Everyone,

I'm currently developing a project that includes several similar modular units with several instrumentation and pumps package.

The thing is that the electrical classification of the area where the equipment and instruments are to be installed is Class 1, Div 2, and installation must follow NEC 500 (NFPA 70) requirements.

I'm having problems identifying which conduit system may be used in the unit we are developing. In general, we have many restrictions on space, and the uses of explosion-proof fittings are quite difficult to implement based on the limited area that we have available.

Nevertheless, these are the main features of the items that we have:

- Motors are Class 1, Division 1 Rated (3 phase - 460 V)
- Instruments Type 01: Explosion-proof enclosure (120 Vac) power supply and contact switch (for signal control) contained in the instrument enclosures
- Instruments Type 02: Explosion-proof enclosure with intrinsic safety circuits-24 Vdc. Power supply/signal control comes from the same cable - loop powered).
- Instruments Type 03: Intrinsically safe circuits (NEMA 4X enclosure)-24 Vdc. Power supply/signal control comes from the same cable - loop powered).
- Junction Boxes: Explosion-Proof type NEMA 7: Inside includes some elements able to generate arcs or sparks (Instruments type 01 are connected to these elements).

Questions:

1. Can I fit EYS seals with one male NPT extreme directly in an explosion-proof enclosure (Junction Box, enclosure motor, or instruments type 02)?

I cannot find anything about this, all I can find is that you need first a union Type UNY connected to the enclosure, a conduit Rigid Nipple, and then the Seal. Due to space limitations, I would like to omit the UNY union where possible and just connect the seal directly​

2. Do I need to use "seals" for instruments type 02 and 03 that have intrinsically safe circuits?

3. Can I connect directly to the enclosure a UNL elbow type explosion-proof instead of a UNY union?

See reference for this in the attached picture, otherwise is basically UNL105 from eaton​

Spoiler

4. Can I use Liquid flexible metal conduit (LFMC) UL Listed with liquid-tight connectors (also UL listed)instead of rigid conduit?

I'd like to apply this on the terminal box motor, and some instruments in general. In motors, I would prefer not to use an explosion-proof flexible conduit such as ECGJH type, since they are not very malleable and also very expensive​

5. Instruments type 01 need to be connected first to a Junction Box explosion-proof enclosure, do I need to use 2 seals, 01 for the entry at the junction box and the other one to be used at the entry of the instrument?

Please have into account that the distance that separates these elements is really short and is even less than the 18" (450mm) required by NEC to install seals. See attached pictures for references​

Spoiler

6. I have 4 possible options for the motor terminal box conduit system connection, where my favorite is number 2, I can also use options 3 and 4, option 1 is basically excluded due to space limitations. In any case, can you tell me which ones are more suitable and meets NEC codes? See pictures below.

Spoiler

7. When leaving Class 1 Division 2 area to an unclassified area, I understand that a seal is necessary. In my case, the boundary is exactly at the location of the cable tray system. My doubts are detailed in the attached picture.

Spoiler

I apologize for the long post, hopefully, some of you may help me with this misconception that I may have.

Regards

 

[Gr8blu]

trolex I'll try to answer your questions in order.
First things first - ALL equipment (including the seals, elbows, junctions, drains, conduit runs, and actual apparatus) MUST be labelled as appropriate for the hazardous location(s). You CAN use a CL I/Div 1 item in a CL I/Div 2 location, but not the other way around. You ALSO are required to have the gas group identified (Group A thru D) as part of the labelling because different gases have different ignition points. Lastly, the label must also include HOW the item is protected (intrinsically safe, explosion-proof, purge/pressurize, hermetic seal, etc.)

1. Use of EYS seal (direct to explosion-proof enclosure): Review 501.15(A)(1) Exceptions - there are a few instances where the seal is not required. I don't know enough about you specific devices/sensors to be able to tell you whether you can claim an exception or not. Otherwise ...
In theory, you can. However, what that means is that you are effectively blocking the wiring at the exit of the junction box. That in turn means that whatever that junction box is attached to becomes a "throw away" part because there is nowhere to break the lead run and make a reconnection to the existing conduit runs. Do you really want to be on the hook for replacing motors, sensors, etc. every time something goes wrong? Better to keep a bit of distance between the EYS (or EZS) seal and the junction box. Another reason for the "extension" between seal and enclosure is that the elbow is often the low point of the run - which means it needs to be designed as the "drain" for that section (enclosure to seal).
2. Use of seals (intrinsically safe circuits): Per 501.15(A)(1) - If the intrinsically safe circuit contains components that may produce arcs, sparks, or temperature excursions OR has a 53+ mm entry, the seal is required. The only exceptions occur when all devices in the intrinsically safe circuit are: 1) hermetically sealed, or 2) immersed in oil, or 3) enclosed in a factory-sealed (so labeled AND properly labelled for the EXACT classification including Class, Division or Zone, and Gas designation) enclosure, or 4) "nonincendive" circuits.
3. Use of UNL vs UNY: Depending on the end user and local authority you might be able to use just the UNL instead of adding the UNY as well. However, not all locations will allow you to do so. One of the arguments of having the UNY section is that it makes assembly and disassembly of the equipment from the conduit run that much easier (because it is an "inline" section, rather than a "directional bend" section).
4. Use of "flex" conduit vs rigid: For most US end-user locations, this is a NO. If the intended installation is in Canada, it is absolutely NO. Rigid conduit only. Note that this is the case for all CL I locations and most CL II locations, independent of Division or Zone. Also note that some end users may require stainless runs only.
5. Use of multiple seals (JB, instrument): Per 501.15(A)(3) - if the two end points are not more than 900 mm apart AND the seal can be installed not more than 450 mm from either junction with equipment, a single in-line seal is permissible. The distances would be measured between the ends of the box (or device) connector to each other to determine total length ... or to the ends of the seal fitting to determine that distance.
6. Choice of routing options (1 thru 4): For all the routing options, you will almost certainly be required to have a drain provision at the lowest point of the run between junction box and seal AND between device and seal. Being connected to the motor and its JB will guarantee you have a possible moisture ingress point. With this in mind, the only real choices you have are options 3 and 4.
7. Transitioning from one classification to another (CL I/Div 1 to CL II/Div 2): Per 501.15(4)(B)(2) and Exception Nos. 2 and 3 - The seal can be located anywhere within 3.05 m of the boundary plane. I prefer to install the seal at least 300 mm from the boundary, on the "unclassified" side, so the "classified" conduit runs through the boundary layer. Just for reference, the boundary CANNOT be "right at the end of the cable tray" - except if the boundary is also a physical wall between "indoor" (classified) and "outdoor" (unclassified). Whichever side of the boundary you install the seal on, recall that it has to be readily accessible.

Converting energy to motion for more than half a century