Using a meyers hub on a 10x10x6 Explosion Proof Enclosure

Joseph.Rhodes34

Electronic Technician
Location
Tuscaloosa,Alabama
Occupation
Electronic Technician / Electrician
I've got this little project going on over at the digester's building of our plant. It's a hazardous location due to the chemicals and dangerous associated with the digesting process (very similar to enzymes breaking down what's in your stomach). I'm using this rather bulky and quite expensive hub-less 10x10x6 explosion proof boxes as a meeting point for the analog wiring that will give us some information from level and flow meters to our VTScada. I was wondering if I could use meyer hubs for the connector of the pipe I've been running. I've been around explosion proof things before, but on a much smaller scale.
 

rbalex

Moderator
Staff member
Location
Mission Viejo, CA
Occupation
Professional Electrical Engineer
There are several considerations but ultimately it is unlikely that a Myers hub will be suitable.
  • What is the electrical area classification?
  • What are the internal wiring methods and equipment inside the enclosure?
  • Is the enclosure required to be sealed?
  • If the enclosure is already threaded, what is the purpose of the Myers hub?
 

Joseph.Rhodes34

Electronic Technician
Location
Tuscaloosa,Alabama
Occupation
Electronic Technician / Electrician
  1. Class I, Division I & II
  2. Backplate with terminal block strip 4-20mA industry standard (18-2 Shielded)
  3. No
  4. The enclosure is not threaded
 

rbalex

Moderator
Staff member
Location
Mission Viejo, CA
Occupation
Professional Electrical Engineer
  • Division 1 requires the enclosure to be explosionproof [Section 501.15(A)(3)] unless it meets another suitable protection technique found in Section 500.7. None were suggested as applicable in the OP.
  • Unless there is a 2" or greater entry, the enclosure is not required t be sealed. [Section 501.15(A)(1)]
So far so good; however, how are raceways supposed to enter a non-threaded explosionproof enclosure? Section 500.8(E) suggests threading is necessary to maintain the integrity of explosionproof systems.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
It is not uncommon to find explosion proof enclosures with no conduit openings. We take them to a machine shop and have them threaded for NPT at the locations where we want the conduit entry. Typically there are some instructions provided as to the required threads.
 

kwired

Electron manager
Location
NE Nebraska
It is not uncommon to find explosion proof enclosures with no conduit openings. We take them to a machine shop and have them threaded for NPT at the locations where we want the conduit entry. Typically there are some instructions provided as to the required threads.
Presuming there is wall thickness enough to get at least 5 threads as required by 500.8(E)(1)
 

kwired

Electron manager
Location
NE Nebraska
I've got this little project going on over at the digester's building of our plant. It's a hazardous location due to the chemicals and dangerous associated with the digesting process (very similar to enzymes breaking down what's in your stomach). I'm using this rather bulky and quite expensive hub-less 10x10x6 explosion proof boxes as a meeting point for the analog wiring that will give us some information from level and flow meters to our VTScada. I was wondering if I could use meyer hubs for the connector of the pipe I've been running. I've been around explosion proof things before, but on a much smaller scale.
I don't know what knowledge or experience you have with this kind of thing, but part of the reason for threaded entries and threaded covers on these explosion proof enclosures is so that when there is any explosion inside the hot gas will have to be forced around the threads and will be cooled by the surrounding metal before it makes it to the outside where if it hadn't been cooled it could ignite the environment on the outside. A meyers hub has a rubber seal but any minor failure of that seal would be an easy path for such incident to allow fire/hot gas to make it's way out without first being cooled while passing through the threads like it is supposed to work.

Because it works like this you also are not supposed to use any kind of thread sealing compounds on your threaded components. That will not allow the pressure to escape through the preferred paths and force things to find other paths if it can.
 

rbalex

Moderator
Staff member
Location
Mission Viejo, CA
Occupation
Professional Electrical Engineer
As far as the threading of the explosion proof, I'm doing that in shop.
So far, others, including yourself, have acknowledged the enclosures will ultimately be threaded. How or why one gets there may be open to discussion. Nevertheless, what then is the perceived value of using a Myers hub?
 

Joseph.Rhodes34

Electronic Technician
Location
Tuscaloosa,Alabama
Occupation
Electronic Technician / Electrician
I was not sure if running this threaded conduit into this 10x10x6 explosion proof box was more beneficial than using a Meyers hub. This project isn't being inspected. It's a get it done type situation, but I wanted to know more about what code has to say with using meyer hubs.
 

rbalex

Moderator
Staff member
Location
Mission Viejo, CA
Occupation
Professional Electrical Engineer
I was not sure if running this threaded conduit into this 10x10x6 explosion proof box was more beneficial than using a Meyers hub. This project isn't being inspected. It's a get it done type situation, but I wanted to know more about what code has to say with using meyer hubs.
Inspected or not, it needs to meet Code. If the enclosure required sealing, a Myers hub would be prohibited outright. [Section 501.15(A)(1) (last sentence) and Section 501.15(B)(1) with its cross-reference to Section 501.15(A)] Since a seal isn't required, I still don't see any value for a Myers hub that a union, if necessary, wouldn't cover.

BTW it's Myers, not Meyers,
 

Joseph.Rhodes34

Electronic Technician
Location
Tuscaloosa,Alabama
Occupation
Electronic Technician / Electrician
With this kind of installation being the first time I've done this sort of thing. It can be intimidating and a bit out of my league. It's ok because I'm always willing to learn more and can accept mistakes. I appreciate all of the wisdom, I really do...
 

dkidd

Senior Member
Location
here
Occupation
PE
With this kind of installation being the first time I've done this sort of thing. It can be intimidating and a bit out of my league. It's ok because I'm always willing to learn more and can accept mistakes. I appreciate all of the wisdom, I really do...
Mistakes like explosions?:cry:
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Presuming there is wall thickness enough to get at least 5 threads as required by 500.8(E)(1)
From the Crouse Hinds Catalog sheet for GUE and GUE explosion proof enclosures.
Bodies have thick walls so they can be factory or field drilled and tapped to meet NEC/CEC requirements for Class I hazardous areas
They also have drawings and tables that specify the maximum size and maximum number openings that can be field installed, as well as the locations where these openings are permitted. Additional instructions specify NPT and the depth of the threads.
 
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