C1 , D2 Underground Conduit

[Electricman13.8]

Good day fellow Electrician's,
I was seeing if someone could shied some light on my issue, please.. I work at chemical factories.. We have conduit leveeing a C1, D2 ( Class 1 , Division 2 ) area with a Seal-off before going into ground ( We do have installed ) ...Do I need another Seal-off at the point it enters the GP ( general Purpose Area ) ..? All area EX fittings ( Explosion Proof ) What are the classifications, when the conduit enters the ground, does it still require the 10' rule under ground..? Does it need another Seal-off after leveeing the classified area & surfacing into the GP area..? I have looked in Section 500 in the great book, but I just don't see it in plane English / Black & White understandable ( for me ,LoL ) ..Thank you .

 

[rbalex]

This can become a LOOOOONG discussion. There are some exceptions, but historically, the underground is unclassified. The seals you have already installed are boundary seals per Section 501.15(B)(2). Unless they are also doing double-duty as equipment seals per Section 501.15(B)(1) they are not required to be explosionproof. [See the last sentence of Section 501.15(B)(2)] If the other end of the run enters an unclassified location there is no classificarion boundary and no seal is required.

Some of the aforementioned exceptions to the above statement would be in installations covered by Sections 511.8, 513.8, 514.8, and 515.8. They each have special rules.

A side note: Attempting to classify from the NEC, except for installations subject to Articles 511 to 515, is a waste of time. Other Standards, such as those listed in Section 500.4(B) IN No. 2 should be consulted. In your case, NFPA 497 would be a likely choice.

 

[Electricman13.8]

Thank you Sir,
I appreciate the quick response & you enlightening me on this question.. ..

 

[Geo57]

I have a similar issue. My question involves sealing a conduit that begins in a Cl 1 Div 2 area, and then is routed underground for approximately 50 feet then comes back above ground in the same Cl 1 Div 2 area. It then transitions from the conduit stub up to a ladder type tray. In our facility (a chemical plant) we handle heavier than air hydrocarbons so we consider low areas such as sumps and underground locations CL 1 Div 1. As I understand it the proper installation is to have seals at both places where the conduit transitions from above ground to underground since there is an area class change.
However given the purpose of sealing to prevent gas from migrating from hazardous to unhazardous locations it seems unnecessary to have the seal where the cable transitions to an open tray. Is there something I am missing in the exceptions? Neither end of the cable is connected to any type of pressurized process. It is just a power feeder to a TEFC motor.

 

[rbalex]

As I mentioned in my first response, "This can become a LOOOOONG discussion."

Since your facility has opted to declare the underground Class I, Division 1, (unnecessary in my opinion, but perfectly legal) you have shifted the boundary conditions of the original post (OP) to a Section 501.15(A)(4) installation and neither of its Exceptions apply. In this case, the seals at grade must be "full-blown" Section 501.15(C) and located as required by Section 501.15(A)(4). BTW explosionproof seals are not just for "... the purpose of sealing to prevent gas from migrating from hazardous to unhazardous locations." See the opening statement of Section 501.15 IN No. 1.

From your description, since the transition of the cable beyond the Division 1/Division 2 boundary appears to be wholely in the Division 2 location, a new set of rules apply. Depending on the cable Type, sealing will need to be per Section 501.15(E); most likely Subsection 501.15(E)(3).

Just curious since it won't change the installation, but is the reason both stub-ups are in the "same" Division 2 location because they are classified from the same actual source or just because they happen to be classified the same way.

 

[Geo57]

I appreciate the response. The cable type for this installation is type TC cable. The reason both stub ups are in the same division is just that there wasn't a way to support the conduits from the pipe rack to where the pumps are located (there are four pumps each with its own conduit), so the contractor ran the last 50 feet or so over to pumps from the cable tray by going underground. It is really just a case of geographical location. We will have the contractor modify his installation to add the seal where the conduit stubs up to the tray which is the end which was left unsealed.

 

[rbalex]

Type TC is a Subsection 501.15(E)(3) application. No transition seal is necessary.

 

[rbalex]

Type TC is a Subsection 501.15(E)(3) application. No transition seal is necessary.

Oops sorry, Type TC may need to consider Subsection 501.15(E)(1) if the feed end originates in an enclosure that is required to be explosionproof.

 

[Geo57]

I reviewed some of the other threads around this subject, and have a better understanding now. Thanks Bob, I appreciate the input.