Class II environment Motor Control Center?

[Jraef]

I have to replace an ancient MCC in a Class II Division 1 environment (sugar mill). The old one was grandfathered in because I don't think sugar was considered explosive at the time this was built-out in the 60s, so it is not NEMA 9 or anything, plain old NEMA type 1 enclosures, not even gasketed! The buckets are full of sugar dust. My customer said he is getting a bid from someone telling him that they can put an MCC in a Class II area. I don't believe it, I think some noob is mixing up the concepts, as in NEMA Class II MCC, meaning inter-wiring between buckets, and UL Class II Division 1 explosive dust environment. But here in California we rarely come across grain elevators or mills where this is an issue, so I thought I'd throw it out there to some of you in more "grainy" areas of the country. Anyone ever heard of an MCC mfr willing to somehow build one that would pass NEMA 9? Or is there some "trick of the trade" I am unfamiliar with, such as purging the structure?

My fall back position is to tell him it can't be done, that he either has to have us pipe in a bunch of separate NEMA 9 enclosed starters, or move the entire MCC to a non-classified environment, neither of which is likely to get funded.

 

[petersonra]

I would be inclined to just pressurize the room. It is a common practice and not real expensive.

 

[smoothops10]

Is partitioning an option?

NFPA 499 excerpt
6.4.6.1 Only unpierced solid walls make satisfactory barriers in
Class I locations, whereas closed doors, lightweight partitions, or
even partial partitions could make satisfactory walls between
Class II, Division 1 locations and unclassified locations.
6.4.6.2 Area classification does not extend beyond the wall,
provided it is effective in preventing the passage of dust in
suspension or layer form.

May want something more robust but products as simple as these may fit the bill.
https://www.globalwrap.com/dust-barrier-wall
http://www.zipwall.com/

Not sure anyone makes a NEMA 9 dust-ignitionproof MCC.

 

[petersonra]

I seem to recall that you are not required to have any special enclosure in a CIID2 area other than it being dust tight. it should not be real hard to create a D2 area. Then you could use an MCC with type 12 enclosure.

 

[rbalex]

Sugar milling was Class II, Group G even in the 60s. (maybe even earlier)

The first question I would ask though is, "Is it even Class II dust?".

Combustible Dust [as applied to Hazardous (Classified) Locations].
Dust particles that are 500 microns or smaller (i.e., material passing a U.S. No. 35 Standard Sieve as defined in ASTM E11-2015, Standard Specification for Woven Wire Test Sieve Cloth and Test Sieves), and present a fire or explosion hazard when dispersed and ignited in air
(rbalex underline mine)

My inclination, is it isn't.

 

[Jraef]

I seem to recall that you are not required to have any special enclosure in a CIID1 area other than it being dust proof.

Really? That would be great if true. But everything I see says it must be dust explosion proof for Division 1, aka NEMA type 9. Article 500.7 does say dust proof (which might mean NEMA 12?) is OK for Division 2 though, so thanks for bringing that up because you made me read Article 500 again to be sure and 500.8.C.6 says that if Dustight is acceptable, it need not be marked for hazardous location use. So that may raise another option, seeing if they can somehow lower the area classification to Div. 2.

 

[Jraef]

Sugar milling was Class II, Group G even in the 60s. (maybe even earlier)

The first question I would ask though is, "Is it even Class II dust?".

My inclination, is it isn't.

I had actually visited this site back in around 1978 in another life and looked at this very same MCC at that time, because they were thinking even back then of replacing it. Like I said, it is not explosion proof now, wasn't then, and I don't recall that having been discussed as an issue either. There are other newer (70s vintage) MCCs and Switchgear in there as well, none of it is explosion proof. But they mentioned that anything new must now be rated for Class II Div. 1, so I figured something had changed in the code since I was these 40 years ago.
Here's a picture of the old MCC, there is another one right behind me (I took the picture) and an old 40's vintage Westinghouse Switchboard.

it's hard to tell completely, but sectioning this area off from the rest of the mill is going to be all but impossible.

 

[rbalex]

I had actually visited this site back in around 1978 in another life and looked at this very same MCC at that time, because they were thinking even back then of replacing it. Like I said, it is not explosion proof now, wasn't then, and I don't recall that having been discussed as an issue either. There are other newer (70s vintage) MCCs and Switchgear in there as well, none of it is explosion proof. But they mentioned that anything new must now be rated for Class II Div. 1, so I figured something had changed in the code since I was these 40 years ago.
Here's a picture of the old MCC, there is another one right behind me (I took the picture) and an old 40's vintage Westinghouse Switchboard.
it's hard to tell completely, but sectioning this area off from the rest of the mill is going to be all but impossible.

You need to reread Section 502.5:

Explosionproof Equipment. Explosionproof equipment
and wiring shall not be required and shall not be
acceptable in Class II locations unless also identified for
such locations.

Been that way for years.

Section 502.10(A)(3) is your basic Class II, Division 1 enclosure requirement:

Boxes and Fittings. Boxes and fittings shall be provided
with threaded bosses for connection to conduit or
cable terminations and shall be dusttight. Boxes and fittings
in which taps, joints, or terminal connections are made, or
that are used in Group E locations, shall be identified for
Class II locations.

Sugar is Group G; dusttight is sufficient "identification". Group E is the only one that needs real extra-special attention.

502.115 Switches, Circuit Breakers, Motor Controllers,
and Fuses.
(A) Class II, Division 1. In Class II, Division 1 locations,
switches, circuit breakers, motor controllers, fuses, push
buttons, relays, and similar devices shall be provided with
enclosures identified for the location.

Remember, identified, doesn't necessarily mean listed/labeled.

Dusttight should be adequate for the application.

 

[don_resqcapt19]

There was a huge sugar dust explosion in Georgia in February of 2008. There were huge accumulations of dust all over that were placed into suspension by the first small explosion.

 

[Jraef]

You need to reread Section 502.5:

Been that way for years.

Section 502.10(A)(3) is your basic Class II, Division 1 enclosure requirement:

Sugar is Group G; dusttight is sufficient "identification". Group E is the only one that needs real extra-special attention.

Remember, identified, doesn't necessarily mean listed/labeled.

Dusttight should be adequate for the application.

Thanks for the input.
Hmm, interesting take on it, and the existing installation would seem to add credence to your interpretation (although it's not even dust tight now). I'm more inclined to think, after reading more about the groups and such, that since it is only POWDERED sugar that is in Group G, I'm betting that they originally were not processing powdered sugar, only granulated and now they are doing powdered, hence the change.

Believe me, I WANT to accept your interpretation, but I'm skeptical. Your underlining in 502.5 leaves out the last part of that sentence, "... unless also identified for such locations." which I would take to mean it DOES need to be identified for use in Class II Div. 1. Your interpretation of 502.10(A)(3) is leaving out the "or" if you interpret that as saying that it is ONLY Group E by the way. If I apply the "or" only to that part of the statement it is located in, and remove it, it reads differently.

Boxes and fittings in which taps, joints, or terminal connections are made, or that are used in Group E locations, shall be identified for Class II locations.

Either way, I'm actually not being asked to interpret their NEED for Classified equipment, only the feasibility of it and it appears this is a no-go. I'm going to tell them they have to move the MCC out of the classified area, construct a room around it and purge it, or we will give them an array of NEMA 9 enclosed individual starters on a rack. That's going to look very odd next to the old gear, but that isn't something I can control.

Don, very interesting article, thanks. I may include that link in my proposal.

 

[rbalex]

Section 502.5 just says explosionproof in and of itself means nothing in Class II.

Group E is ALWAYS Division1 [Section 500.5(C)(1)(3)] and it usually scares me to death.

Powdered sugar can be troublesome; however, it is worth the trouble reviewing NFPA 499 with regard to housekeeping and dust abatement. It isn't difficult to reduce Class II, Division 1 to Division 2.

 

[Jraef]

Section 502.5 just says explosionproof in and of itself means nothing in Class II.

Group E is ALWAYS Division1 [Section 500.5(C)(1)(3)] and it usually scares me to death.

Powdered sugar can be troublesome; however, it is worth the trouble reviewing NFPA 499 with regard to housekeeping and dust abatement. It isn't difficult to reduce Class II, Division 1 to Division 2.

Yes, actually that was going to be my other suggestion, reducing it to Div 2. Thanks for the reminder.