Burial Depth Under Slab_ Hazardous Location

[Curt Fitz]

Hello, Everyone...
We are installing an outdoor hydrogen refueling system (for the forklift fleet) at an automobile plant. Our conduit is sch. 40 PVC with RGC risers for the stub-up locations. We have typically relied upon Table 300.5 to determine our burial depth for these facilities. One of the project managers (naturally) questioned the burial depth, stating that 514.8 should be considered for the installation because the location was Class 1 (Divisions 1 & 2). My argument was that because the entire location is under a 6" concrete slab outside a building, that 300.5 applied. What say you?

 

[Dennis Alwon]

I agree with the project manager



514.8(C) Nonmetallic Conduit.


Rigid polyvinyl chloride conduit (PVC), reinforced thermosetting resin conduit (RTRC), or high-density polyethylene conduit (HDPE) shall be permitted where buried under not less than 600 mm (2 ft) of cover. Where PVC conduit, RTRC conduit, or HDPE conduit is used, threaded rigid metal conduit (RMC) or threaded intermediate metal conduit (IMC) shall be used for the last 600 mm (2 ft) of the underground run to emergence or to the point of connection to the aboveground raceway. An equipment grounding conductor (EGC) shall be included to provide electrical continuity of the raceway system and for grounding of non–current-carrying metal parts.
ENHANCED CONTENT
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Where polyvinyl chloride conduit (PVC), reinforced thermosetting resin conduit (RTRC), or high-density polyethylene (HDPE) conduit is used for underground wiring, threaded rigid metal conduit or threaded steel intermediate metal conduit must be used for the last 2 feet of the underground run to the point of emergence or to the point of connection to the aboveground raceway. These rigid nonmetallic conduits, including any nonmetallic conduit elbows and fittings, must be located not less than 2 feet below grade, as illustrated below.

 

[Dennis Alwon]

Here is an enhanced content which gives some explanation.

514.8 Underground Wiring.
All underground wiring shall comply with 514.8(A), (B), or (C).

ENHANCED CONTENT
If fuel spilled in the vicinity of gasoline dispensers seeps into the ground, it could migrate into underground electrical conduits. Therefore, all conduits installed below the hazardous locations of a motor fuel dispensing facility are required to be sealed within 10 feet of the point of emergence from below grade. This boundary seal minimizes the passage of gasoline or other fuel vapors into unclassified locations where the electrical equipment is not explosionproof or otherwise protected. Tables 514.3(B)(1) and (B)(2) define the extent of the aboveground Class I, Divisions 1 and 2 locations.

 

[augie47]

Agree,,,, That was an issue in our area on gasoline dispenser and brought up at a Statewide meeting where the Code gurus agreed PVC 24" for the full length until transition to metal even under building slabs.