Rigid Conduit.

[chevyx92]

I don't install much rigid but I need to bury 40FT of 1/2" RMC. One end will stub up out of soil and the other will stub up out of concrete. PVC is not an option because of depth issues and being subject to damage and can't use PVC coated rigid either as supplier doesn't carry 1/2" and not waiting to order it. My question is what are you guys doing to provide corrosion protection as required by 334.10(B)?

 

[big john]

3M 50/51 pipe wrap. It's a black tape specifically designed to protect conduit in corrosive environments.

 

[infinity]

Do you have some sort of corrosive soil condition? Isn't RMC already galvanized for direct burial?

 

[chevyx92]

Do you have some sort of corrosive soil condition? Isn't RMC already galvanized for direct burial?

I don't known soil content but 344.10(A) states that protection from corrosion solely by enamel shall be permitted ONLY indoors and in occupancies not subject to severe corrosive influences. 344.10(B) states that RMC is permitted to be installed in concrete and in direct contact with the earth where protected by corrosion protection. So to me that means additional protection is needed besides the enamel only.

 

[big john]

344.10(A) would not be applicable because the hot-dip galvanizing is not "enamel." That refers more to the type of coating you see on a weatherpoof Bell box.

..344.10(B) states that RMC is permitted to be installed in concrete and in direct contact with the earth where protected by corrosion protection. So to me that means additional protection is needed besides the enamel only.

This is the section I've seen cited when people use pipe wrap, but it is not universal: Some places GRC will rot in the ground, some places it lasts forever. It really depends on local conditions. For what it's worth the UL listing for GRC says this:

Rigid Ferrous Metal Conduit (DYIX)
...Galvanized rigid steel conduit installed in contact with soil does not generally require supplementary corrosion protection....

 

[chevyx92]

344.10(A) would not be applicable because the hot-dip galvanizing is not "enamel." That refers more to the type of coating you see on a weatherpoof Bell box.

I disagree. I believe the "enamel" is the coating the NEC references when it says in 344.10(A) Ferrous raceways and fittings protected from corrosion solely by "enamel" shall be permitted "only" indoors and in occupancies not subject to severe corrosive influences.

If indeed the "enamel" the NEC is referring to is something other than the "coating" you're calling it, then what is the "enamel" the NEC is talking about on RMC that is to be installed indoors only?

 

[don_resqcapt19]

I disagree. I believe the "enamel" is the coating the NEC references when it says in 344.10(A) Ferrous raceways and fittings protected from corrosion solely by "enamel" shall be permitted "only" indoors and in occupancies not subject to severe corrosive influences. ...

I don't think any "enamel" coated conduit has been on the market in the last 40 or 50 years.
Here is the information from the UL White Book for "Rigid Ferrous Metal Conduit (DYIX)"

Corrosion Protection and Coatings.

Galvanized rigid steel conduit installed in concrete does not require supplementary corrosion protection.


Galvanized rigid steel conduit installed in contact with soil does not generally require supplementary corrosion protection.
In the absence of specific local experience, soils producing severe corrosive effects are generally characterized by low resistivity (less than 2000 ohm-centimeters).


Wherever ferrous metal conduit runs directly from concrete encasement to soil burial, severe corrosive effects are likely to occur on the metal in contact with the soil.

As far as I know all of the rigid steel conduit on the market at this time is "galvanized".

 

[big john]

I disagree. I believe the "enamel" is the coating the NEC references when it says in 344.10(A) Ferrous raceways and fittings protected from corrosion solely by "enamel" shall be permitted "only" indoors and in occupancies not subject to severe corrosive influences.

I agree that is what that section is referring to, but enamel is a separate finish from galvanizing. Notice that in that section it doesn't refer to "galvanized steel," rather simply to "ferrous raceways and fittings."

This supported by 314.40 that lists them as two separate forms of protection:

Metal Boxes, Conduit Bodies, and Fittings.
(A) Corrosion Resistant. Metal boxes, conduit bodies, and fittings shall be corrosion resistant or shall be well-galvanized, enameled, or otherwise properly coated inside and out to pre*vent corrosion.

But this is a moot point because the UL listing for rigid conduit specifically permits it to be installed in non-corrosive soil conditions without additional protection.

 

[tom baker]

Where the corrosion takes place on RMC is right where the conduit comes out of the slab. The 3M 50/51 pipe wrap works well. Does you supplier carry PVC coated nipples, use that for coming out of the slab.

 

[JDB3]

}}Where the corrosion takes place on RMC is right where the conduit comes out of the slab. The 3M 50/51 pipe wrap works well. Does you supplier carry PVC coated nipples, use that for coming out of the slab. {{

I am in agreement. A lot of the utility companies around here, that are now using metal poles (in place of the treated wood ones) put a coating on them, starting just below grade & continue up a short distance above grade.