Encased duct bank depth

[tbentley]

Table 300.50 identified minimum duct cover requirements for both general and special conditions. These minimum cover depths would seem appropriate for direct buried ducts but do not seem to recognize the benefits or protection of concrete encasement. For example a rigid steel conduit need only have 6 inches of cover whereas a nonmetallic conduit requires 18 inches of cover. If the nonmetallic conduit were encased and 3 inches beneath the top of the encased bank, would that not provide equivalent protection to the RGS conduit and allow a shallower depth.

Similarly, could not a concrete-encased duct bank be less than 24 inches beneath a parking lot surface?

If you have technical references permitting shallower depths for concrete-encased ducts, I'd appreciate those references.

 

[bphgravity]

Though your argument seems logical for the most part, the Code does not appear to make this consideration.

 

[steve66]

But 300.5 states "Direct-buried cable or conduit or other raceways shall be installed to meet the minimum cover requirements of table 300.5"

If you provide "concrete encasement", isn't that different than "direct bury"?

If that is the case, couldn't you say Table 300.5 does not apply to concrete encased conduits?

Steve

 

[iwire]

I sure hope Steve has it right.

I just finished a duct bank that transitions from 5' underground to about 3' above ground.

 

[tbentley]

But 300.5 states "Direct-buried cable or conduit or other raceways shall be installed to meet the minimum cover requirements of table 300.5"

If you provide "concrete encasement", isn't that different than "direct bury"?

If that is the case, couldn't you say Table 300.5 does not apply to concrete encased conduits?

Steve[/QUOTE]

I referenced table 300.50 for >600 volts versus 300.5 for <600 volts. The paragraph that directs you to Table 300.5 indeed refers to direct buried cable and ducts. However, the paragraph that directs you to Table 300.50 does not specifically allude to direct buried. In fact there is a Note at the bottom of Figure 310.60 that also directs you to Table 300.50 and paragraph 310.6(A) defines "electrical ducts" as embedded in earth or concrete. Thus, the claim is made that Table 310.50 applies even if the ducts are encased in concrete. Hence although we have PVC ducts encased in concrete, it has been claimed that the shallowest duct must have 18 inches of cover in general conditions.