Depth of Cover / Class 1 div. 1 boundary

[tlawler]

I do contract labor for an electrician/piping contractor. We are doing a gas station and installed power, intercom, sensor conduits at the dispensers and submersible pumps. The conduit at the dispenser sumps and pump sumps is rigid and is 2' below grade. We extended these conduits with pvc into a building, after coming through the wall at top of footer we sloped pvc up to an elevation of about 1' below finished floor elevation. We turned the conduits up in a 10'stick of rigid bent with 90 which has a seal-off and into a nipple which terminates in a trough. The inspector said that the pvc had to be 24" below grade. If we are outside the 20' radius of class 1 is it legal to use the standard minimum cover? Or does the class 1 boundary extend to the end of the conduit?

Thanks in advance,

Tim Lawler

 

[rbalex]

Re: Depth of Cover / Class 1 div. 1 boundary

?Technically,? there is nothing wrong with your installation as I understand your description. Had I been the AHJ representative, I would have accepted it. ?Legally? may be another matter because it has more to do with the philosophy of how one interprets Code.

Section 514.8, Exception 2 is what permits you to use RNC in the first place. It is my opinion that Exceptions are not ?stand alone? and should be interpreted or applied in the context of the primary rule; in this case, the main text of 514.8.

The main rule makes no depth specification; it simply specifies RMC shall be used below the locations classified by the Tables. The exception permits RNC if it has a 2ft cover. Properly interpreted, the 2ft cover is only required below the locations classified by the Tables. This assumes that all other requirements of 300.5 are met.

 

[hardworkingstiff]

Re: Depth of Cover / Class 1 div. 1 boundary

I disagree, and believe the inspector is correct. 514.8 exception 2 specifically says you need 2' of cover.

I wonder if the cover is what "they" determine would be required to contain an explosion if it should occur. Remember the fiberglass tank that exploded in Florida? That tank probably had 3-4 feet of cover and a concrete pad over it. If I remember correctly, the explosion raised the concrete pad a few feet in the air.

If you had less than 2' of cover over a conduit that contained vapors that exploded, it might not be contained.

 

[hardworkingstiff]

Re: Depth of Cover / Class 1 div. 1 boundary

Originally posted by tlawler:
Or does the class 1 boundary extend to the end of the conduit?

At one time the code specifically said the class 1 boundary did extend to emergence from ground of the conduit from a classified location. Whether it is still there or not I do not know.

 

[rbalex]

Re: Depth of Cover / Class 1 div. 1 boundary

As I said originally, it?s largely a matter of the philosophy of interpretation. I explained my process.

Art 514 is a bit unique. Originally it was largely extracted from NFPA 30 and later NFPA 30A. There was a definite attempt to avoid conflicts even when CMP14 believed the NFPA 30(A) requirements were excessive. The currently reconfigured 30A TC is more attuned to CMP14 than before as evidenced by the redrawing of Figure 514.3 which now clearly shows in the 2005 NEC that the area below the Classified locations are NOT classified themselves. This is now more consistent with the philosophies of the NFPA 497 TC and API RP500.

There is no technical substantiation for the 24? cover. The IS technical substantiation for a 2? concrete encasement as reflected in 501.4(A)(1) Exception. It has been tested by several major refiners. I?m fairly confident in saying this since I was co-author of the proposal to create the Exception and we researched the 514 requirements. We left the 24? cover requirement only to avoid conflict since we could not find documented substantiation.

As you have noted, considering the location Classified Division 1 to the point of emergence is no longer a requirement.

Edited to correct the reference from NFPA 496 to 497

[ December 14, 2005, 05:10 PM: Message edited by: rbalex ]

 

[john m. caloggero]

Re: Depth of Cover / Class 1 div. 1 boundary

Tim: I must agree with Bob Alexander.
John Caloggero

 

[tlawler]

Re: Depth of Cover / Class 1 div. 1 boundary

Thanks for all the replies. The inspector told me I had to either use all rigid or put the pvc 2' below finished floor. I tried to ask him why the code would require 2' of cover under the building when we were way outside of the 20' radius of Class I Division I and he just said that the code requires 2' of cover because of exception no 2 to 514.8 and the fact that it says until the conduit conduit emerges from the ground.

Thanks again for the information.

Best regards,

Tim Lawler

 

[hardworkingstiff]

Re: Depth of Cover / Class 1 div. 1 boundary

Originally posted by tlawler:
... and the fact that it says until the conduit conduit emerges from the ground.


Tim Lawler

Tim,

The code used to say that, but Bob says it was removed. Did you show that section to you?