Jas6100

I have been searching for information to support my arguement that Compression type EMT fiitings are to be used in a Class II Div II installation and not Set Screw fittings. Am I wrong about this?

Manufacturers and the NEC both describe concrete tight acceptance but do not mention dust tight. Is my view just skewed by common practice?

John Valdes

Try this site. You may have more luck. Sorry, but I have no answer for you. Welcome to the forum!

http://forums.mikeholt.com/forumdisplay.php?f=65

KayJay

I don’t even see anything in the UL Whitebook for dust tight fittings.
Other than the requirements for threaded entries for enclosures, boxes and a couple of references to covers being designed not to allow dust to accumulate, so I think you could use either type of fitting.
Liquidtight with listed fittings is also allowed in CL II, Div II, so it stands to reason that a fitting that is raintight would be acceptable, but I don’t see this written as a requirement anywhere.

Article 100 defines dusttight, which appears to imply that other than the requirements for boxes, enclosures and covers, fittings would only have to be adequate for the task at hand and not specifically listed for the application. That's my best guess so far.

This seems to carry over even into the requirements for the seals for raceways between dust/ignition proof enclosures and other locations in addition to the other ways permitted in 502.15 to prevent dust from entering these enclosures.
There appears to be no requirement for any special type of seal fitting, meaning explosion proof seals aren’t required, but you could certainly use an EY or EYS if you wish. You could most likely use a standard C or LB fitting packed with duct seal as a seal fitting if you wanted as long as the cover was gasketed and arranged so that it wouldn’t allow dust to accumulate on it.

Jas6100

Thank You both for your posts. I have contacted manufactures for information but as yet have not recieved a response.

LJSMITH1

Sorry about the delay in responding to this posting, I just noticed it.

Let me start off by saying, it should not be your responsibility to determine the classification of a specific hazardous area or to select the product that would be acceptable in that area. These locations and requirements are defined by OSHA Standard 1926.407 Hazardous Classified Locations, and various NFPA and insurance guidelines.

You can take the necessary steps to ensure the product is listed for the specific application/location that has already been defined by the proper authority or the NEC.

Unfortunately, "Dust-Tight" is not a rating category in UL886, which is the governing specification for Hazardous Location Boxes and Fittings. However, it is mentioned as an exception to evaluate Class II fittings and boxes.

From UL886:

A box or fitting need not be exposed to the circulating dust-air atmosphere if all joints:
a) Are of the threaded type, or

b) Are ungasketed and comply with the requirements in 6.1.1, and 6.2.1.4 – 6.2.4.4

As you are aware, there are two primary types of fittings for EMT: Set Screw and Compression. Within the compression types, there are two sub-types of UL Listed compression fittings “Raintight” and "Concrete-tight". “Raintight” fittings for EMT have a separate conduit sealing ring or solid gland ring to prevent the entrance of water.

I suggest that if EMT conduit is used in this abnormal dust condition, that a compression type fitting be used. If there is water spray exposure, you would want to install a “Raintight” fitting that would prevent the entrance of water mixed with dust. FYI...Inspectors around the country are now enforcing that fittings in a wet location be UL Listed Raintight.

Note these various definitions from UL514B, UL1604 & UL886 ; for equipment designated to meet the following conditions "Raintight," or "Rainproof" - testing designed to simulate exposure to a beating rain will not result in entrance of water. "Liquidtight" - equipment is so constructed that liquid does not enter the enclosure when subjected to a spray of mineral oil. "Driptight" equipment is so constructed that falling moisture or dirt does not enter the enclosure. "Dust-tight" - equipment is so constructed that circulating or airborne dust does not enter the enclosure.

With that being said, there is no specific requirement for Compression type fittings to be used in a Class II Div 2 environment. However, from the information above, there would be a high confidence level about using a raintight compression fitting in this application.

I hope that helps.

__________________
Larry