Article 501.15(B)(2)

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Dale001289

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Construction is pulling TC-ER, 600V, multi-conductor cable to low-voltage loads, typically via cable tray to PVC conduit underground ductbank with very little above grade, rigid-metal conduit utilized.
Two scenarios:
· Scenario 1: Cables enter the duct bank system off cable tray ‘water-falls’ from a piperack in a non-hazardous area. They route underground to Division 2 areas where they stub-up for motors and their associated control stations.
In Division 2, they're installing conduit boundary seals and routing ‘free-air’ to the motor termination box where they connect using Crouse-Hinds TMCX connectors.
At the non-hazardous side, whereit enters the duct bank, there is no conduit boundary seal at the stub-up.

· Scenario 2: Exactly like scenario 1 except both ends stub-up in Division 2 area, yet neither end has conduit boundary seals.

Are either of these scenarios a violation of 501.15(B)(2)?
 
rbalex said:
How are the boundaries documented? [Section 500.4(A)]
How is below grade classified?
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The only boundaries I'm aware of are shown on the Area Classification drawings, based on API RP 500 and NFPA 497. There is no reference to underground; only above grade.
 
The truth is, I am rarely concerned about Division 2/unclassified boundaries. Generally, where are sufficient gases and vapors coming from in Division 2 to worry about? CMP 14 isn't concerned too much either as indicated by removing the requirement for such boundaries to use explosionproof seals.

I don't believe most Division 2/unclassified boundaries need to be sealed at all especially if they are not explosionproof.

You are describing one of a few exceptions that I have: the boundary between above and below ground and I believe it should be explosionproof. FWIW, CMP 14 however isn't concerned with that case either and recent industrial experience seems to bear them out.

So, there is no boundary between the above ground/underground unclassified location in Senario 1 and no seal is required at all.

In both Scenarios, if the stub ups are in the same Division 2 location what good would seals do? If they stub up into two different Division 2 locations, there might be some benefit. In any case, they still would not have to be explosionproof.
 
rbalex said:
The truth is, I am rarely concerned about Division 2/unclassified boundaries. Generally, where are sufficient gases and vapors coming from in Division 2 to worry about? CMP 14 isn't concerned too much either as indicated by removing the requirement for such boundaries to use explosionproof seals.

I don't believe most Division 2/unclassified boundaries need to be sealed at all especially if they are not explosionproof.

You are describing one of a few exceptions that I have: the boundary between above and below ground and I believe it should be explosionproof. FWIW, CMP 14 however isn't concerned with that case either and recent industrial experience seems to bear them out.

So, there is no boundary between the above ground/underground unclassified location in Senario 1 and no seal is required at all.

In both Scenarios, if the stub ups are in the same Division 2 location what good would seals do? If they stub up into two different Division 2 locations, there might be some benefit. In any case, they still would not have to be explosionproof.
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Ok, I will take this as the final word on a topic that has been debated intensely on this particular project. Thanks again Bob.
 
Dale001289 said:
Ok, I will take this as the final word on a topic that has been debated intensely on this particular project. Thanks again Bob.
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Actually, it isn't "debated intensely" by the technical committees for NFPA 497 or API RP 500. In fact, it's rarely even discussed. It does raise its head occasionally at the IEEE/PCIC conferences. Fortunately, the NFPA 497 and API RP 500 technical committees are well represented there too.
 
rbalex said:
Actually, it isn't "debated intensely" by the technical committees for NFPA 497 or API RP 500. In fact, it's rarely even discussed. It does raise its head occasionally at the IEEE/PCIC conferences. Fortunately, the NFPA 497 and API RP 500 technical committees are well represented there too.
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Bob: What would be some examples of non-explosion proof seals?
 
Dale001289 said:
Bob: What would be some examples of non-explosion proof seals?
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Good question; CMP14 has never seen fit to actually answer it. This is Emerson's answer. The response is fairly recent (January 14, 2015). Emerson is also currently represented on CMP14 through Appleton.

Some have suggested that a non-shrinking duct seal might be suitable.

As I mentioned above, I personally don't believe most Division 2/Unclassified boundary seals are necessary at all; but those few that are necessary should be explosionproof.
 
rbalex said:
Good question; CMP14 has never seen fit to actually answer it. This is Emerson's answer. The response is fairly recent (January 14, 2015). Emerson is also currently represented on CMP14 through Appleton.

Some have suggested that a non-shrinking duct seal might be suitable.

As I mentioned above, I personally don't believe most Division 2/Unclassified boundary seals are necessary at all; but those few that are necessary should be explosionproof.
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Thanks for your response.

Dale
 
Dale001289 said:
Bob, field is suggesting RTV silicone caulk be used for non-explosion proof 'seals'. Thoughts?
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This may seem petty, but I would avoid using a listed seal fitting; you would be violating Section 110.3(B) since the fitting is listed for use with a specific sealing compound.

The overall installation would need to be sold under Section 500.8(A)(3). Since I believe most (but not all) Division 2/Unclassified boundaries don't need a seal in the first place, I'd probably buy it. In those cases where I would want a seal, I would want it to be explosionproof.
 
Table 501.1 - conduit seals entereing pressurized buildings

Table 501.1 - conduit seals entereing pressurized buildings

Bob, I have another scenario regarding seals - Topic: conduits entering pressurized rooms (in this case, prefabricated Substation by Powell Electric). The building is located in a non-hazardous location. Existing Conduits containing multiconductor cables (mostly Low-voltage TC-ER type) enters the building from an adjacent Division 2 area (approximately 50' away) and all have Crouse-Hinds explosion proof seal fittings. If this is considered a boundary seal is it really required, noting 501.15 (A)(2)? And if not, how does the building maintain its pressurization which, in this case is tied into the Fire and Gas system?
Can the seal be a non-explosion proof type as you described in a previous post?

Thanks in advance - Dale
 
A couple of key questions first.


  1. Are the conduits run underground?
  2. Since the run originates in a Division 2 location and terminates in an unclassified location, there must be a boundary somewhere and some form of seal has to be installed. Where does your documentation indicate the boundaries are? [Section 500.4(A)]

(Since you're quickly becoming a "pro" at this, the term is unclassified not "nonhazardous". Just because there's no flammable gases involved doesn't mean there aren't other dangers. ;))

I can answer part of your question. Maintaining pressurization depends on the capability of the system provided by the manufacturer. Sealing raceways and other openings is a good idea but not an absolute necessity if the system is large enough.
 
rbalex said:
A couple of key questions first.


  1. Are the conduits run underground?
  2. Since the run originates in a Division 2 location and terminates in an unclassified location, there must be a boundary somewhere and some form of seal has to be installed. Where does your documentation indicate the boundaries are? [Section 500.4(A)]

(Since you're quickly becoming a "pro" at this, the term is unclassified not "nonhazardous". Just because there's no flammable gases involved doesn't mean there aren't other dangers. ;))

I can answer part of your question. Maintaining pressurization depends on the capability of the system provided by the manufacturer. Sealing raceways and other openings is a good idea but not an absolute necessity if the system is large enough.
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1. The conduits are not underground; they're routed into a cable tray from respective loads above grade in the process units, mostly LV loads, i.e. 460V motors and associated controls.
2. There are no boundary seals shown on documentation and after reviewing the installation on site, none have been installed. I've informed the client this a violation of 501.15(B)(2) - but they've stated "conduit seals at the building would suffice".

My instincts tell me the new (4" Al) conduits entering the building should be sealed for pressurization only with non-explosion proof type(?) - then another seal, such as C-H EYS installed within 10 feet of the Division 2 boundary where TC-ER cable transitions to conduit.
 
Post #12 mentioned TC cables, but not trays - that changes the analysis. With a transition from conduit to tray outdoors, it sounds like you may have a case where Section 501.15(B)(2) Exception No. 2 applies. It's one of the toughest exceptions to understand because it only applies to the conduit itself, not the cable(s) inside. Basically, no boundary seal for the conduit is required in an outdoor transition case because it would be useless anyway.

Sections 501.15(E)(1)&(3) apply to the TC cables. Depending on which edition of the NEC you're using, it may take a bit of parsing the text but you will find that no seals are required for TC cable at the boundary either. There could be some in the Division 2 enclosures.

Section 500.4(A) only requires the boundaries to be documented, not necessarily the seals. (It's OK to document their locations too, just not required)

Sealing conduits at the building to maintain pressure is fine, just not an NEC classified locations requirement since those particular conduit segments aren't crossing any boundaries. Of course, there may be other NEC sealing requirements, such as condensation reduction, that may exist.
 
rbalex said:
Post #12 mentioned TC cables, but not trays - that changes the analysis. With a transition from conduit to tray outdoors, it sounds like you may have a case where Section 501.15(B)(2) Exception No. 2 applies. It's one of the toughest exceptions to understand because it only applies to the conduit itself, not the cable(s) inside. Basically, no boundary seal for the conduit is required in an outdoor transition case because it would be useless anyway.

Sections 501.15(E)(1)&(3) apply to the TC cables. Depending on which edition of the NEC you're using, it may take a bit of parsing the text but you will find that no seals are required for TC cable at the boundary either. There could be some in the Division 2 enclosures.

Section 500.4(A) only requires the boundaries to be documented, not necessarily the seals. (It's OK to document their locations too, just not required)

Sealing conduits at the building to maintain pressure is fine, just not an NEC classified locations requirement since those particular conduit segments aren't crossing any boundaries. Of course, there may be other NEC sealing requirements, such as condensation reduction, that may exist.
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Excellent response. This really helps.
 
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