additional exterior coating of galvanized rigid steel co

[budwalsh]

Since navigating the NEC can be a challenge for a civil engineer like myself, my question concerns instances where NEC stipulates application of an additonal orgainc (bitumastic) coating of concrete encased galvanized rigid steel conduit.
It would be very helpful to me to know if such a stipulation does or does not exist within the NEC, and if it does, exactly I can find it.
Thanks, Bud Walsh

 

[charlie b]

Re: additional exterior coating of galvanized rigid steel co

I didn?t know what ?bitumastic? means, so I looked it up (combination of asphalt and filler used to coat metals to protect them from corrosion). But the NEC does not contain a single word that begins with ?bit.? Also, the 8 hits I found under ?organic? did not seem to apply to your question. But this might help:

300.6 Protection Against Corrosion.
Metal raceways, cable trays, cablebus, auxiliary gutters, cable armor, boxes, cable sheathing, cabinets, elbows, couplings, fittings, supports, and support hardware shall be of materials suitable for the environment in which they are to be installed.
- - - - - - - - - -
(B) In Concrete or in Direct Contact with the Earth. Ferrous or nonferrous metal raceways, cable armor, boxes, cable sheathing, cabinets, elbows, couplings, fittings, supports, and support hardware shall be permitted to be installed in concrete or in direct contact with the earth, or in areas subject to severe corrosive influences where made of material judged suitable for the condition, or where provided with corrosion protection approved for the condition.

 

[don_resqcapt19]

Re: additional exterior coating of galvanized rigid steel co

From the UL Guide for Rigid Ferrous Metal Conduit.

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.

Conduit that is provided with a metallic or nonmetallic coating, or a combination of both, has been investigated for resistance to atmospheric corrosion. Nonmetallic outer coatings that are part of the required resistance to corrosion have been additionally investigated for resistance to the effects of sunlight.

The requirement for additional corrosion protection must be based on the type of soil conditions where the conduit is being installed. Pay close attention to the section about going from concrete encasement to soil. This will cause serve conrrosion in most types of soil and additional protection should be used for this application.

Don