501.15(B)(2) Change for 2005

[jcross]

"Conduits shall be sealed to minimize the amount of gas or vapor within the Division 2 portion of the conduit form being communicated to the conduit beyond the seal. Such seals shall not be required to be explosion proof but shall be identified for the purpose of minimizing passage of gases under normal operating conditions and shall be accessible."

My question is, if you don't have to set an "explosion proof" seal such as an "eys" then what is "identified for the purpose" Can we use a "C" condulet and pack it with duct seal?

 

[petersonra]

Re: 501.15(B)(2) Change for 2005

I suppose if one of the makers of the sealing compound were to identify their compound as suitable for such an application, it might fly.

 

[rbalex]

Re: 501.15(B)(2) Change for 2005

It is important to read this change in context. It applies only to "boundary seals."

I must admit I'm ambivialent about it. I disagreed with the original substantiation and some of the CPM's "wordsmithing" with respect to the NEC undefined term "normal." On the other hand, I didn't see that it makes enough difference to worry about.

 

[petersonra]

Re: 501.15(B)(2) Change for 2005

Bob - just curious

What was the substantiation and why did you not agree with it?

 

[jcross]

Re: 501.15(B)(2) Change for 2005

The main reason I brought this up is I do a lot of inspections in the petro-chemical industry. This will substantially lower the cost of the installation if our installers don't have to set explosion-proof seals at Division 2 boundaries as well as properly pouring them to boot. The way I interpret this is no different than the sealing requirements mentioned in 300.7(A)? Opinions........

 

[rbalex]

Re: 501.15(B)(2) Change for 2005

Originally posted by petersonra:
Bob - just curious

What was the substantiation and why did you not agree with it?

That?s a fair question ? It?s difficult to answer without going fairly deeply into the entire philosophy of both electrical area classification and sealing.

The short answer is, ?If you believe the seal is necessary at all, it better be explosionproof.?

This was the original Substantiation:

Substantiation:
Seals in conduits passing from Division 2 locations into unclassified locations are needed to prevent the passage of gases or vapors, not to contain explosions in the conduit system as is the case with Division 1 conduit systems. This proposal will allow same type seals as permitted in 504.70 for intrinsic safe installations. The existing text (501.5(B)(2)) eludes to this: "sealing fitting...shall be designed and installed so as to minimize the amount of gas or vapor within the Division 2 portion of the conduit from being communicated to the conduit beyond the seal". However, it is now common practice to require explosion proof seals. Explosion proof seals are expensive and make it difficult to modify wiring once installed. This proposal will make it clear that explosion proof seals are not required as boundary seals between Division 2 and unclassified locations.

I disagree with the first sentence of the Substantiation ? the rest of the Substantiation is therefore based on what I believe is a false premise.

In my case, I believe most Division 2/Unclassified boundary seals are unnecessary in the first place. Remember, by definition there are no ignitable gases in Division 2 under ?normal? conditions, and unless there is a specific motive force unique to the raceway, there are no gases to "minimize." However, if you do believe that ignitable concentrations are available to migrate you must also be concerned about how they will be ignited. In the case cited in the Substantiation, (504.70) there is no ignition source in the raceway, but for ?common? Division 2 installations a short(and not necessarily in the raceway itself) is all it would take. As an additional comment ?regular? seals aren?t vapor proof either. See 501.5. FPN No.1.

 

[nhee]

Re: 501.15(B)(2) Change for 2005

Rbalex,

Is it realistic to consider any "boundary seal" able to contain an explosion/ignition that occurs within the raceway? Take, for instance the case of a 2" RMC conduit passing into a Div. 1 area and travelling 10-20' before it hits the devices/equipment it is feeding, along with their seals. Wouldn't the "pressure-piling" of an ignition within this conduit be more than the boundary sealing fitting was designed to withstand? Is the fitting able to do anymore than limit the migration of gas/vapor?

I think I agree with your argument that in Div 2, boundary seals may not be necessary at all. But if it is required, I don't know that it needs to be explosion-proof (if a non-explosion-proof/listed sealing fitting is available, have not seen one).

 

[rbalex]

Re: 501.15(B)(2) Change for 2005

I'll let our new moderator, Steve Norako, explain the details, but a properly installed seal should have no problems with pressure-piling in the conduit. The UL hydrotests (not sure the exact numbers) are in excess of the expected pressures. After a sufficent distance (again not sure how far) the effects of pressure piling becomes constant.

 

[petersonra]

Re: 501.15(B)(2) Change for 2005

I may get more interested in this subject. I was in my bosses office a few minutes ago and saw some paperwork labeled UL698 on it.

 

[buildingellicott]

Re: 501.15(B)(2) Change for 2005

NYBFU does electrical inspections for me. Recently an electrician smelled faint scent of gasoline when he opened the conduit trough from the fueling stations in a 2-year-old facility. We found that the sealing compound had shrunk, and all said this was "normal." They put in more sealing compound, but I wonder if re-sealing should be a routine requirement? In a disaster at either end, can fire and/or explosion travel a few hundred feet through 1-inch (or so) conduit and spread the disaster to the other end? It seems this could happen either by a spark in the interior service room or by fire/explosion at the fueling areas. Am I too worried?

 

[rbalex]

Re: 501.15(B)(2) Change for 2005

buildingellicott,

You have several issues here; but, to answer your question, yes, an explosion can travel several hundred feet through a raceway system. This is one of the reasons I said in an earlier post, ?If you believe the seal is necessary at all, it better be explosionproof.?

Issue two - listed sealing compounds, properly mixed and installed, expand; shrinkage is not normal. Contact the seal manufacturer for the appropriate compound and fill instructions.

Third, and most important, you need to find out how gasoline is getting into the raceway. If the installation is less than two years old, there is possibly a leakage problem.

 

[buildingellicott]

Re: 501.15(B)(2) Change for 2005

Thank you for the information. This is a great forum, and I thank all who share their experience and insight here.