Table 300.5

[mshields]

The second row of Table 300.5 is; In trench below 2 inches thick concrete or equivalent.

Column 3 is Nonmetallic Raceways Listed for Direct Burial without concrete encasement or other approved Raceways.

I've always thought it was strange that there is no column for Nonmetallic Raceways WITH concrete encasement insofar as this is a very common practice. Any insights as to why there is no such column

And related to that what about that second row category indicating that the depths in that row are for any one of the Wiring Methods under 2 inches of concrete. I have always assumed that this is referring to a slab above the conduit. BUT if you have a ductbank with a minimum of 2 inches beyond the conduits, clearly the conduit has 2 inch concrete above it. Granted, it has 2 inches of concrete below it, to the right, to the left, etc etc etc. Is this in fact the row that ought to be used for a traditional Sched 40 PVC duct bank with 2 inches of concrete all around?

Thanks,

Mike

 

[steve66]

That's always confused me too. I think you are right. But I've always just specified the absolute worst case depth for whatever row and column seem like it could apply to a particular project, just to make sure it meets code.

Note that row 2 only says " 2" concrete cover", while row 4 specifically says " 4" concrete exterior slab".

That combined with general note #2 which talks about concrete encased conduits leads me to believe that row 2 does apply to concrete encased conduits.

 

[Smart $]

See Note 2. Granted, somewhere the logic seems to fail but I don't feel like making a truth table to prove it...

 

[Ingenieur]

Ref the Note for figure 310.0
it references Table 300.50
so for pvc in concrete column 3 is used
column 2 for rigid
you measure to the top of the upper duct, not the top of the duct bank
max is 30"

 

[mshields]

Figure 310.0???

Figure 310.0???

Did you miss a digit? Also, while I realize 300.50 is similar, I am focused on 300.5 for the moment.

 

[mshields]

Yes but

Yes but

Steve66 - I realize you're generally agreeing with me that it is unclear. But regarding the reluctant conclusion you did make; if row 2 wording includes concrete encased and you are planning on using PVC encased in concrete, the only column available to you is Column 3 which is for Direct buried "without concrete encasement". i.e. they kind of cancel each other out.

With regard to note 2; if you encase your conduit because the conduit is not rated for direct burial, suddenly, you don't have any columns available to you.

 

[Ingenieur]

Steve66 - I realize you're generally agreeing with me that it is unclear. But regarding the reluctant conclusion you did make; if row 2 wording includes concrete encased and you are planning on using PVC encased in concrete, the only column available to you is Column 3 which is for Direct buried "without concrete encasement". i.e. they kind of cancel each other out.

With regard to note 2; if you encase your conduit because the conduit is not rated for direct burial, suddenly, you don't have any columns available to you.

It doesn't exclude concrete encasement
only that the pvc must be LISTED for direct burial use without concrete encasement

fig 310.60's note refers directly to 300.5
the fig is associated with concrete banks

you can't use a conduit not listed for db, with or without concrete encasement

you are convoluting the issue imho

 

[Smart $]

...
With regard to note 2; if you encase your conduit because the conduit is not rated for direct burial, suddenly, you don't have any columns available to you.

When the PVC is listed for direct burial without concrete encasement, you use Column 3.

When the PVC is not listed for direct burial (and approved for burial where concrete encased mind you), you use Note 2 AND Column 3... which only changes the depth to the top of the conduit in rows "Under a building" to 2" (of concrete) and "Under minimum of 102 mm (4 in.) thick concrete exterior slab..." to 6" (4" for the slab and 2" minimum for the concrete encasement. No change to depth in other rows.

If you have PVC conduit not approved or listed for burial in any fashion, you can't use it. I do not know if any exists.

 

[steve66]

Steve66 - I realize you're generally agreeing with me that it is unclear. But regarding the reluctant conclusion you did make; if row 2 wording includes concrete encased and you are planning on using PVC encased in concrete, the only column available to you is Column 3 which is for Direct buried "without concrete encasement". i.e. they kind of cancel each other out.

With regard to note 2; if you encase your conduit because the conduit is not rated for direct burial, suddenly, you don't have any columns available to you.

Yes, I think Ingenieur and Smart have it right. So the title of column 3 refers to the listing of the conduit, and not with how the conduit is actually installed.

So standard PVC conduit direct buried is Row 1 column 3 = 18" deep , and covered or encased in 2" of concrete is R2 C3 = 12".

If I can throw another wrench into the topic, what if you have your concrete encased PVC running 12" deep and you go under a road or alley? Do you get to stay at 12", or does it have to dive down to 24"?

 

[mshields]

head spinning

head spinning

am going to have to have another cup of coffee