Truss Manufacturing Plant

[arnettda]

Hello,
Am I correct in the following thinking
I am adding a saw in a Truss manufacturing Plant. (Wood Trusses for buildings) In the rooms with the actual saws there is a lot of fine saw dust that accumulates on everything. I believe these rooms to be a Class 2 Division 2 location? They do housekeeping but higher up the dust accumulates and even down low it is present. . And in the middle of the day there can be large amounts of saw dust on the floor.
EMT is my wring method and I am using compression fittings?
From 110.28 informational note they talk about the types of enclosures that are considered dust tight. 3R is not listed but through my supplier a 3R/5 /12box would be considered dust tight?
What do I use for ceiling boxes for my lighting? The standard W/P box with threaded hubs and then weather proof blank covers? I am going to talk with my supplier about dust proof light fixtures, or some type of fixtures where dust will not accumulate on the top of the fixture.
Any other helpful information would be greatly appreciated.

 

[MTW]

Sounds like they need a dust collection system. To greatly reduce he hazard.

 

[don_resqcapt19]

Saw dust is typically a Class III location as the particles are too large to be considered combustible dust.

 

[zbang]

Oh, it'll burn, all right . There's the coarse dust off a wide circular blade and much finer off a thin band-saw or drum sander. Really depends on how much hangs in the air. (Off to look at the classifications again, I'm hardly ever in that territory.)

 

[rbalex]

Oh, it'll burn, all right . There's the coarse dust off a wide circular blade and much finer off a thin band-saw or drum sander. Really depends on how much hangs in the air. (Off to look at the classifications again, I'm hardly ever in that territory.)

Unless there is fine sanding involved, sawdust is Class III. It will certainly burn but is more subject to a flash fire rather than an explosion. Still dangerous of course. Depending on the cycle, combustible dust has been variously defined in Articles 100, 500, or 502. Currently, it resides in NFPA 499, Part 3.3.3 as 500 microns or smaller.

 

[zbang]

And there's the subtle difference between detonation and deflagation... mostly sub-sonic vs super-sonic, which tends to track with explosion vs very-quick-fire.

(goes to look at 499...)

 

[rbalex]

Now let's get back to the OP:

• Has someone qualified to do so "properly documented" the classification per Section 500.4?
• Enclosures with a Type 5 or 12 rating are dusttight.
• EMT is suitable for Class II, Division 2, OR Class III (either Division).
• See Section 502.10(B)(4) or 503.10(A)(2) as appropriate. (There is virtually no difference between Class III wiring methods permitted for Divison 1 or 2.)
• See Section 502.130 or 503.130 as appropriate.

 

[tortuga]

What do I use for ceiling boxes for my lighting? The standard W/P box with threaded hubs and then weather proof blank covers?

Keep in mind while this is standard practice for wet locations a compression EMT fitting is not UL listed for use without a locknut.

 

[brantmacga]

Keep in mind while this is standard practice for wet locations a compression EMT fitting is not UL listed for use without a locknut.

So using a compression fitting in a threaded entry without the locknut is a violation? I guess I’m confused about what purpose that would serve.

What about a rain-tight fitting into a Myers hub on top of a can?


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[petersonra]

Is any EMT fitting listed for use without a lock nut?

 

[ptonsparky]

Is any EMT fitting listed for use without a lock nut?

Oh, crud. All those LBs I’ve used. Nothing is grounded properly!

Oh, wait, I pull green every where. I’m good.

 

[tortuga]

Is any EMT fitting listed for use without a lock nut?

No
This came up years ago on a project, I might have an old thread about it on here.
It went around and around with inspectors, then the manufacturer, then UL
I saved the email I got for future reference:

UL Certifies (Lists) Conduit Fittings under the product category for Conduit Fittings (DWTT), located on page 141 of the 2015-16 UL White Book, pdf located atwww.ul.com/whitebook and also on UL Product Spec at www.ul.com/productspec and enter DWTT at the category code search field. In the guide information you will find that with or without a gasket/seal, all male threaded fittings and nipples have only been investigated for use with locknuts only and have not been evaluated for use with hubs.

To expand just a little further, even grounding and bonding hubs that are certified and provided with a certified grounding or bonding locknut have not been evaluated for use with conduit fittings. They serve in a manner similar to grounding and bonding bushings except they are only for use with threaded rigid metal and intermediate metal conduit

If I recall correctly it was accepted placing the locknut above the rantight plastic seal, then treading it into a hub.
It made me aware of the broader issue of the code requiring more and more things to be listed, seems like a good idea on the surface, then you find out the listings are so narrow in an attempt to deflect lawsuits that the listing renders a product useless in a common install, like a rain tight fitting into a bell box.