Table 300.50

[Sparky2791]

I have a 12470 kV Duct bank with 4" PVC conduits encased in a 4" concrete envelope I plan on placing the duct bank @ 18" below grade (column 2) no vehicular traffic. There is a section of the duct bank where i need to raise the conduits to up so there is only +- 15" of cover. I am wondering if the 4" Concrete envelope around the ductbank allows me to use column 4 so the loss of 3" of cover is not a code violation. This 3" loss in cover would only be for 8' of distance prior to passing through the retaining wall as I will gradually slope the conduit slope the conduit up to the correct height to pass through the retaining wall on top of the retaining wall footer. Once it passes through the retaining wall foundation it will have plenty of cover on the other side.

The Code says 'Under buildings or Exterior concrete slabs' Duct bank is not a concrete slab but still 4" of concrete.


My other option is to transition to PVC coated GRC in the duct bank for the portion of conduit that will not have the 18" of cover. Column 3 tells me I only need 6" of cover min.

Thanks for replying!

 

[Hv&Lv]

Why do you need to raise the duct?
solid rock?

would note 2 or possibly note 3 be in play here?

 

[Sparky2791]

If I do not raise it I would need to lower to dive under the retaining wall I am passing through because the footer is in the way. Top of footer is at 36". 18" of cover plus duct bank depth of 20" = 38" to bottom of duct bank.

 

[Sparky2791]

Why do you need to raise the duct?
solid rock?

Sorry forgot to reply to you directly
If I do not raise it I would need to lower to dive under the retaining wall I am passing through because the footer is in the way. Top of footer is at 36". 18" of cover plus duct bank depth of 20" = 38" to bottom of duct bank.

 

[Hv&Lv]

Sorry forgot to reply to you directly
If I do not raise it I would need to lower to dive under the retaining wall I am passing through because the footer is in the way. Top of footer is at 36". 18" of cover plus duct bank depth of 20" = 38" to bottom of duct bank.

Industrial application where note 3 would come into play?

 

[Sparky2791]

Industrial application where note 3 would come into play?

Nice! That will work. I broke one of my most cardinal rules - Did not read all the footnotes. Surprised they allow it to be reduced to 6" but Ill take it!

 

[Sparky2791]

Industrial application where note 3 would come into play?

Another question - does note 3 apply to column 6 in the table?

 

[Hv&Lv]

Another question - does note 3 apply to column 6 in the table?

Note 3 applies to all columns.