Iron oxidation on rigid metal conduit at grade level

[Peter Furrow]

About once a month I get a call to replace the old 2” rigid metal conduit that stubs up from the ground into the bottom of the meter can. The iron oxidation that occurs on the rigid metal conduit is always more noticeable or prominent right at grade . The conduit always breaks right at the soil line . Just below grade the conduit is rusted but not broken, it’s still in tact. Just above grade the rigid metal conduit is intact.
I’m an electrical contractor in the coastal area here in Florida and I see the strange phenomenon all the time.
Because of this , I have been obsessing this week going down the rabbit hole over Metal alloys, Iron oxidation, galvanizing on conduit & enclosures, powder coating, liquid enamel coating blah blah etc.
Why is the iron oxidation so pronounced right at grade?
Is there a product data information that tells you what metal alloys are used for rigid metal conduit?
Is RMC galvanized with tin or Zinc?
And what about GE , SQ-D , or Eaton outdoor enclosures? I can’t find a product data sheet to tell me what the metal alloys are used for those specific enclosures. Are they galvanized, are they powder coated or are they liquid coated?

 

[wwhitney]

Why is the iron oxidation so pronounced right at grade?

Because it is the location where there is most frequently both moisture (from the ground) and oxygen (from the air). Supplemental corrosion protection at grade and say 12" above and below would be a good idea.

Cheers, Wayne

 

[hbiss]

And what about GE , SQ-D , or Eaton outdoor enclosures? I can’t find a product data sheet to tell me what the metal alloys are used for those specific enclosures. Are they galvanized, are they powder coated or are they liquid coated?

Which is why I would like the NEC to prohibit outdoor panels except for disconnects.

You do realize that meter pans are available in stainless steel?

-Hal

 

[Todd0x1]

Which is why I would like the NEC to prohibit outdoor panels except for disconnects.

Interesting. I have been seeing on public school projects value engineered for the lowest bidder, switchboards, panelboards, and transformers which should really be inside located outdoors to eliminate the square footage needed by a proper electrical room.

 

[don_resqcapt19]

I always require that metallic conduits be wrapped with a corrosion protective wrapping at any concrete to earth interface, concrete to air interface, and earth to concrete interfaces. The corrosion is always the worse at these locations. The UL Guide Information rigid even mentions the concrete to earth interfaces as that is the worst case of the 3 I mentioned. Here is what the Guide Information sheet for "Rigid Ferrous Metal Conduit (DYIX)" says:

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.
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.
Nonmetallic outer coatings of greater than 0.010-in. thickness are investigated with respect to flame propagation detrimental effects to any underlying corrosion protection, the fit of fittings and electrical continuity of the connection of conduit to fittings.
Conduit with nonmetallic coatings has not been investigated for use in ducts, plenums, or other environmental air spaces in accordance with the NEC.
Rigid metal conduit with or without a nonmetallic coating has not been investigated for severely corrosive conditions.

While earth to air is not the same level of corrosion, I see that issue here in Illinois well away from and salt water influences. Most corrosion is a galvanic reaction, a battery if you will, and the moisture along with the materials in the earth is the electrolyte.

 

[kwired]

Which is why I would like the NEC to prohibit outdoor panels except for disconnects.

You do realize that meter pans are available in stainless steel?

-Hal

Typical "loadcenter" not normally available in stainless steel, but a real panelboard might have stainless cabinet options available.

There are a lot of applications where there is no "building" to place a panelboard within and outdoor panels still a necessity.

 

[hbiss]

There are a lot of applications where there is no "building" to place a panelboard within

To me that sounds like a oops on the part of the architect/engineer. Oh, I forgot to provide space for the electrical and mechanical. Just put them outside.

-Hal

 

[Russs57]

Hey, one of the few times you will be glad to see someone used a factory ninety instead of bending pipe.

A few bucks extra on coating or wrap would have made a world of difference. Don't even get me started on electro plated stuff!

 

[kwired]

To me that sounds like a oops on the part of the architect/engineer. Oh, I forgot to provide space for the electrical and mechanical. Just put them outside.

-Hal

I have done a lot of these, trust me inside is pretty inaccessible when in full use.

Livestock buildings - they last a lot longer on the outside, make sure to put duct seal in raceways entering the building and they last a little longer yet.

Many other places where there is power needed but no building to install it in/on.

Most dwellings, retail, offices, and similar I agree that inside is the best place.