In Instrumentation Junction Boxes in our plant, I noticed that cables are entered in the Junction boxes by cable glands through Myers Hubs.

The J.Boxes are EXe. I want to know Is there a reason for using this way and not directly installing the glands to junction boxes without Myers Hubs? Why and when we need Myers Hubs?

 

The hubs allow the cables to be sealed to prevent gas entry into the JB. A sealing compound is poured into the hub.

 

are you sure they are "Myers" hubs?

is this a US installation?

is it a classified area?

IIRC, Ex e boxes are just regular boxes.

This may be a design decision as opposed to some kind of code requirement.

--
Bob
http://ilbob.blogspot.com/

 

If your junction boxes are cast and not sheet metal these are probably not Myers hubs but unions to facilitate the installation of cable glands. Myers hubs are used to provide threaded entries into sheet metal enclosures.

 

Thanks for the replies,We are not using conduit but only cable glands. we are not in USA, we are gas plant so it is classified area. Maybe due to small thickness of the Box (3mm) we have to use this myers hubs? please find below the Box Specifications that I found from the Project document:

MFG: Cooper Crouse-Hinds
Type : Ex-Junction Box
ATEX II2 GD EEx ia II T6 IP66
Dimension: 406 x 305 x 203
1 gland plate (bottom), SS316L Electro-Polished finish, enclosure with horizontal lugs
Complete with terminal rail mounted vertically. Lid fixings are 2 hinges on the left
and 2 bolts on the right c/w M10 External & Internal SS earth stud
Enclosure body thickness: 1.5mm & cover thickness = 1.5mm
Bottom gland plate thickness: 3mm...
Containing the following :
- 10 x NPT 1/2" clearance holes (D22), at bottom, to be taped over for transit purpose,
- 01 x NPT 1 1/4" clearance hole (D42.5), at bottom, to be taped over for transit purpose,
Cable entries are come with SS316L Myers Hubs, plugs or
protect covers as required.

I have photos. Is there a way to send photos in control.com?
<b>Moderator's Note:</b> No you need to use something like dropbox.

 

From this link;
http://www.ehawke.com/technical/wiring-systems-nec.html

Cable Seals, Class 1, Division 1

Cables must be sealed at the termination. The sealing fitting, e.g. a barrier type cable gland, must provide a seal against the passage of gas or vapours through the fitting. Type MC cables with multi-conductors, a gas / vapour tight continuous corrugated aluminum sheath and an overall jacket with a suitable polymeric material must be sealed with an appropriate fitting, e.g. Hawke type 711, after removing the cables jacket and all other coverings so that the sealing compound surrounds each individual insulated conductor. Cables with twisted pairs and shielded cables require the removal of the shielded material or separation of the twisted pairs unless the fitting, e.g. cable gland, is an approved means which minimises the entrance of gases or vapours and prevents propagation of flame into the cable core. If the fitting complies with this requirement, there will be information provided in the fittings installation instructions detailing the means to achieve the seal. Additional testing may be required on the fitting and the style and type of cable to show compliance with the sealing requirements.

An NRTL approved cable sealing fitting e.g. barrier type cable gland, must be fitted onto cables where they enter explosion-proof enclosures.

Further guidance is given in Section 501-5(d) of the NEC.

Cable Seals, Class 1, Division 2
Cables must be sealed at the point of entrance into enclosures that require to be approved for Class I locations. A sealing fitting must comply with the above criteria given in "Cable Seals, Class I, Division 1".

An NRTL approved cable sealing fitting e.g. barrier type cable gland, must be fitted onto cables that enter explosion-proof enclosures.

 

The Myers hubs are there to allow entry into the Ex "e" enclosure, which is probably some kind of sheet metal box, and to have something for your cable glands to screw into to allow the cable entry into the enclosure. If you have cable glands that will directly connect to the enclosure allow entry into this type of enclosure that meet Ex "e" certification, use them.

William (Bill) L. Mostia, Jr. PE
ISA Fellow, SIS-TECH Fellow,
FS Eng. (TUV Rheinland)
SIS-TECH Solutions, LP

"No trees were killed to send this message, but a large number of electrons were terribly inconvenienced." Neil deGrasse Tyson

Any information is provided on a Caveat Emptor basis.

 

This is a link for the Junction Box photo showing the Myers Hubs...

http://s000.tinyupload.com/?file_id=13286235237930921412