Conduit in concrete

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HEYDOG

Senior Member
I have a question on conduit in concrete. Under definition's of "location wet" Installations in concrete slabs are considered a wet location. Does the slab have to be in direct contact with the earth. Is it only called a "slab" if it in direct contact with the earth. If there is concrete on the fourth floor would it be considered a wet location. The conductors are not a concern as most are dual rated. I ask this because for years it has been debated in my code classes. Many say the concrete is wet when poured and that it retains moisture. I say that emt set screw type fittings are listed as concrete tight and are not water tight. I think that there are to many "or's" in the definition. What do you say?
 

ceb58

Senior Member
Location
Raeford, NC
I have a question on conduit in concrete. Under definition's of "location wet" Installations in concrete slabs are considered a wet location. Does the slab have to be in direct contact with the earth. Is it only called a "slab" if it in direct contact with the earth. If there is concrete on the fourth floor would it be considered a wet location. The conductors are not a concern as most are dual rated. I ask this because for years it has been debated in my code classes. Many say the concrete is wet when poured and that it retains moisture. I say that emt set screw type fittings are listed as concrete tight and are not water tight. I think that there are to many "or's" in the definition. What do you say?

This is what I have been told by our state inspectors. If the concrete is on grade then it is considered a wet location and unless there is another protective coating on EMT it cannot be use. PVC must be used. Then,as you have stated,if it were on the fourth floor then EMT with the correct connectors can be use with out a protective coating.
 

chris kennedy

Senior Member
Location
Miami Fla.
Occupation
60 yr old tool twisting electrician
If there is concrete on the fourth floor would it be considered a wet location.

No.

Location, Wet.
Installations underground or in concrete slabs or masonry in direct contact with the earth; in locations subject to saturation with water or other liquids, such as vehicle washing areas; and in unprotected locations exposed to weather.
 

Cow

Senior Member
Location
Eastern Oregon
Occupation
Electrician
I have a question on conduit in concrete. Under definition's of "location wet" Installations in concrete slabs are considered a wet location. Does the slab have to be in direct contact with the earth. Is it only called a "slab" if it in direct contact with the earth. If there is concrete on the fourth floor would it be considered a wet location. The conductors are not a concern as most are dual rated. I ask this because for years it has been debated in my code classes. Many say the concrete is wet when poured and that it retains moisture. I say that emt set screw type fittings are listed as concrete tight and are not water tight. I think that there are to many "or's" in the definition. What do you say?

I thought only the compression type were concrete tight...?
 

dana1028

Senior Member
This is what I have been told by our state inspectors. If the concrete is on grade then it is considered a wet location and unless there is another protective coating on EMT it cannot be use. PVC must be used. Then,as you have stated,if it were on the fourth floor then EMT with the correct connectors can be use with out a protective coating.

I disagree [I think...depending upon exactly what you are saying].

NEC Handbook comment...reciting the UL Guide for Elect. Equipment [White Book] - to paraphrase... Galvanized steel EMT installed in concrete, above grade, generally requires no supplementary corrosion protection.

This is not about wet, it is about the corrosive effects of concrete...as long as the EMT is steel and galvanized...UL accepts EMT in concrete above grade.

Regular, uncoated, ungalvanized EMT in concrete would not be permitted...IMO.

As an inspector, I do not allow regular EMT to be embedded in concrete above grade.
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
I disagree [I think...depending upon exactly what you are saying].

NEC Handbook comment...reciting the UL Guide for Elect. Equipment [White Book] - to paraphrase... Galvanized steel EMT installed in concrete, above grade, generally requires no supplementary corrosion protection.

This is not about wet, it is about the corrosive effects of concrete...as long as the EMT is steel and galvanized...UL accepts EMT in concrete above grade.

Regular, uncoated, ungalvanized EMT in concrete would not be permitted...IMO.

As an inspector, I do not allow regular EMT to be embedded in concrete above grade.


I would say that regular EMT permitted in concrete above grade is permitted. Where are you finding uncoated or non-galvanized EMT?
 

don_resqcapt19

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Staff member
Location
Illinois
Occupation
retired electrician
DYIX.GuideInfo 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.


FJMX.GuideInfo Electrical Metallic Tubing


Galvanized steel electrical metallic tubing installed in concrete on grade or above generally requires no supplementary corrosion protection. Galvanized steel electrical metallic tubing in concrete slab below grade level may require supplementary corrosion protection. In general, galvanized steel electrical metallic tubing in contact with soil requires supplementary corrosion protection. Where galvanized steel electrical metallic tubing without supplementary corrosion protection extends directly from concrete encasement to soil burial, severe corrosive effects are likely to occur on the metal in contact with the soil.
 

don_resqcapt19

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Staff member
Location
Illinois
Occupation
retired electrician
Regular, uncoated, ungalvanized EMT in concrete would not be permitted...IMO.

As an inspector, I do not allow regular EMT to be embedded in concrete above grade.
As far as I know there are only two types of EMT on the market, galvanized steel and aluminum.
 

infinity

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Location
New Jersey
Occupation
Journeyman Electrician
As far as I know there are only two types of EMT on the market, galvanized steel and aluminum.

My thought as well. Regular old steel EMT that I get off the rack at the supply house is permitted in concrete above grade without any additional protection.
 

renosteinke

Senior Member
Location
NE Arkansas
As for the material: Even ten years ago EMT, as well as other metal electrical stuff, were allowed to be 'protected' by only a coat of paint. UL changed its' standard, and now requires at least a minimal zinc coating. It's still possible to find plenty of non-galvanized EMT in older installs. Remember, "paint" can also be a clear laquer. I believe that UL also began to require the materials to pass a second, more demanding corrosion test.

For that matter, there were / are various PVC coated pipes made that have no zinc coating under the PVC. It's quite possible that even rigid conduit was once made by someone with only a PVC coating; it's pretty hard to make an all-encompassing claim on this point.

Bear in mind that there are a variety of methods of coating metal with zinc, with differing amounts of zinc leading to different amounts of protection against corrosion. The state of the industry is such that one cannot assume that both sides of a pipe are coated. I am avoiding the use of the word 'galvanized' here, because the term is sometimes used in a general way, and sometimes as a specific reference to a particular method and coating thickness.

The fittings need not be compression type; many set-screw fittings are listed as 'concrete tight.' The information ought to be on the box. Weathertight fittings are considered 'concrete tight,' but the packaging will not specifically say this; perhaps the White Book expands on this point.

It's my observation that it's not simple moisture, or even alkaline soil / concrete, that causes metal to rust. Rather, it's a combination of moisture AND air. I have excavated many buried EMT runs where the pipe was essentially without corrosion- until it got within perhaps 6" of the surface. At that point, extreme corrosion occurs.

Confounding my expectations, simple 'pipe wrap' tape really does appear effective at preventing corrosion.
 

don_resqcapt19

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Location
Illinois
Occupation
retired electrician
As for the material: Even ten years ago EMT, as well as other metal electrical stuff, were allowed to be 'protected' by only a coat of paint. UL changed its' standard, and now requires at least a minimal zinc coating. It's still possible to find plenty of non-galvanized EMT in older installs. Remember, "paint" can also be a clear laquer. I believe that UL also began to require the materials to pass a second, more demanding corrosion test. ...
I started in 73 and have never installed EMT that was not zinc coated. I have worked on older installations where both the EMT and rigid were coated with paint only.
 

renosteinke

Senior Member
Location
NE Arkansas
I'll agree as to the prevalence of zinc on EMT for a very long time. It's worth noting that the various UL standards (pipe, boxes, panels, whatever) all use the same language and same exposure tests. So, the use of SOME zinc was almost universal for EMT since the early 60's - but this was a manufacturer choice. The panel makers made a different choice, with many of them only painting their 'indoor' stuff.

The rewite of the standard did affect the EMT makers, though. The more substantial weathering tests meant there were now specifications as to the thickness of the zinc. You may not have noticed it as you worked with the pipe, but chances are that you hung some that had but the slightest zinc 'wash' on it. Pipe made since the change - I want to say in the late 90's - has a lot more zinc on it. Oddly enough, that's when the pipe makers also started bragging about their special 'easy pull' interior coatings. Hmmmm.

I'm going by memory here, but IIRC the change in the testing was from a simple high-humidity chamber test to a weakened salt-spray test. For outdoor applications the salt-spray test is ramped up, and there's another corrosive atmosphere test as well. Again, my memory is weak on these details, and I welcome anyone who can provide a better answer.
 
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