Conduit seal offs.. can I exceed 25% fill if not required to be explosionproof?

[Sneak]

Hi,
This question is in regard to an area that goes from a unclassified location to a class 1 div 2 group d (natural gas) location with conduit seals. NEC 2008 section 501.15 (B)(2) states, "Conduits shall be sealed to minimize the amount of gas or vapor....Such seals shall not be required to be explosionproof..." (We are not using "explosionproof apparatus" as our protection method. We are using I.S. and nonincendive circuits)
501.15(C) states "Class 1 Div 1 and 2 seals. Seals installed...shall comply with 501.15(C)(1) through (C)(6). (C)(6) is the 25% (or 40%) fill requirement.

However, the exception immediately below 501.15(C) states: "Exception: seals not required to be explosionproof by 501.15(B)(2) or 504.70"

Since my seals are not required to be explosionproof by (B)(2), I'd think that if 501.15(C) is a "rule" that includes the 25% fill requirement, since there is a valid exception to said rule that would mean that I do not need to abide by it.

My thoughts are that the seal is providing one or two things. Minimizing gas or vapor travel for non-explosionproof applications, and an explosionproof seal for those requiring it. I'd think that the 25% fill requirment is to ensure an explosionproof seal, whereas sealing a seal listed at 25% to, say, 50% fill is sufficient to minimizing gas or vapor travel. Or for that matter, if it is not required to be explosionproof, why couldn't I just use DUX seal?

So, to summarize, 501.15(C) states that seals for Class 1 div 1&2 shall comply with (C)(1) through (C)(6), one of which is the 25% fill requirement.

However, to me it seems that the exception immediately below it exempts me from that requirement.

Does anyone see any holes in my swiss cheese logic? the seals are already installed, although the sealing compound has not been poured, but it would be painful to replace them.

Thanks,
Ken McDonnell

 

[charlie b]

I don't know anything about classified locations, seals, or explosion proof stuff. So I can't help you there. But I know how the code is written. The location of the exception, within the paragraph structure, tells me that it applies to all of 501.15(C). In other words, I agree with your interpretation.

Welcome to the forum.

 

[nakulak]

there are two kinds of xp fittings - 25% fill and 40% fill. I'm no expert, but the fittings are listed for one or the other, and I don't see what any NEC code sections have to do with it other than you can't exceed the fill limit that the fitting is listed for. (In other words, maybe you shouldn't have used an xp fitting, but once you did I think you screwed yourself)

?

 

[zeus87gn]

Ken,

Think about this a little deeper. Although your circuits passing through the Div 2 area are IS or NI, what are they conected to in the safe area? Is the circuitry controlling it capable of producing arcs? If gases propogate through the seal what could happen?

I am not familiar with DUX seal, but if you need a seal for E/P purposes 25% is the rule in those fittings. You may want to protect yourself and replace the seals to be certain the system is safe.

HTH
Z

 

[don_resqcapt19]

The fill rating of an explosion proof seal is only based on the ability to get enough sealing compound around the conductors to provide an explosion proof seal. If the seal is being used only to minimize the passage of vapors or gas and is not required to be explosion proof, I would have no problem using either size seal packed with duct seal or similar product.

 

[don_resqcapt19]

...

I am not familiar with DUX seal, but if you need a seal for E/P purposes 25% is the rule in those fittings. You may want to protect yourself and replace the seals to be certain the system is safe.

HTH
Z

Seals are available in two sizes...one listed for a 25% fill and the other based on a 40% fill. This all goes back to the older codes where conduits were only permitted a 25% fill for new work and a 40% fill for re-work. It was assumed that seals would only be used for new work and they were designed to provide an explosion proof seal when filled to a maximum of 25%. Now with the 40% conduit fill rules, you can use a seal listed for 40% fill or you can use a seal of a larger trade size with reducing bushings.