NEC handbook

[hardworkingstiff]

Page 679 of the 2005 NEC handbook, Exhibit 501.8 shows a "seal at the boundary" on the bottom right hand side of the exhibit.

Am I interpreting 501.15(A)(4) correctly by saying that particular sealoff is not required if this is piped like the picture?

 

[Rockyd]

The seal-off has to be the first fitting inside, or outside, of the established boundary, either side permissable, one EY only, not inside and out.

Don't forget the 25% fill for an EY, unlike the 40% for pipe fill.

 

[hardworkingstiff]

Rocky,

Based on your answer, I believe you agree with me.

 

[rbalex]

Are you assuming the seal below the "red" push-button is less than 10' from the boundary?

 

[hardworkingstiff]

Are you assuming the seal below the "red" push-button is less than 10' from the boundary?

Yes, since no couplings are shown in the drawing (I'm commenting from memory, since I'm out of town and don't have my handbook).

 

[rbalex]

In that case I would agree with your interpretation too although there were a couple of places where unions would probably be needed and they aren't shown either :grin:

 

[Rockyd]

Yuppers Hardworkin' we are in agreement 100% on this one.

(LOL) I may be a member of a union, but I try to design to where I can avoid using them as much as possible. Sure, they have their place, but in everyday work, in a classified space, you can avoid "overusage". I do have to admit that they are great for setting panels (UN's) top and bottom, lest you ever have to pull a panel from a classified space and it has ten pipes coming into it, and no unions!

 

[hardworkingstiff]

Now for the real question.

I have been taught and never really questioned, that coming from a submerged pump at a gasoline underground tank, you must put a sealoff at the pump (now everyone uses sumps, so it is the 1st fitting as the conduit enters the sump) and you must put one where you exit the ground.

I'm thinking now that one sealoff at the sump/pump would suffice providing you use a full 10' length of rigid conduit leaving the sump and do not cross through another classified location.

Thoughts please/thanks.

 

[hardworkingstiff]

I do have to admit that they are great for setting panels (UN's) top and bottom, lest you ever have to pull a panel from a classified space and it has ten pipes coming into it, and no unions!

I hate when someone installs a nipple out of a x-proof box of a pump or dispenser, then the sealoff, then a union. You can do this when you are piping it in, but after the seal is poured, you cannot disconnect the conduit system from the unit being proctected. I often wonder "WHAT ARE THESE GUYS THINKING ABOUT!". (I guess they aren't thinking, and if it is the seal for the 1st fitting exiting the ground, then it's not code compliant).

 

[rbalex]

Exhibit 501.8 doesn’t illustrate boundary seals for underground wiring and the principles are a bit different. See Section 501.15(A)(4), Ex 2.

More relevant references for underground applications in fuel dispensing locations are in Sections 514.8 and 9 and the associated tables 514.3. The Handbook gives a bit of the underlying philosophy.

Article 514 derives much of its material from another source (NFPA 30A).

Historically, underground was “unclassified” except in certain areas specifically defined otherwise in Articles 510-516. There have been movements in the past to consider it “indeterminate.” It hasn’t gone too far because it would set up an entirely new boundary sealing philosophy than most of the experts consider “messy” and the current rules appear to work just fine.

Edit: corrected the term "undefined" to "indeterminate"