Galv Rigid Conduit In Earth

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richwaskowitz

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Shelby Twp. MI, near Detroit
I am looking for a clarification on 344.10(B) in regards to whether it is permissable to use galvanized rigid conduit to feed an illuminated outdoor sign by means of running it down the wall of the building and directly into a trench in earth, cut in the asphault parking lot. I did not see where "galvanized" was mentioned as a "corrosion protection". I want to use rigid as opposed to PVC for the physical protection aspect in order to avoid damage from things such as snow shovelling.
 
The following is from the UL Guide information for Rigid Ferrous Metal Conduit (DYIX)
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.
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Don
 
Thanks Don, but I already read that from an earlier post when I searched for previous info. I guess I was looking for something more in the way of past practice or experience with an inspector rather than a quote from a manufacturer or a standard.
 
don_resqcapt19 said:
Galvanized rigid steel conduit installed in concrete does not require supplementary corrosion protection.
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benaround said:
Rich,

The way I read it, Don is saying if you don't have any concrete go ahead

and use it!!!!
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Are we reading the same thing?

I install rigid in concrete all the time. Those concrete guys really don't care about stubs coming up through the slab and tend to hit them with their machines. Saves a lot of trouble later.
 
The issue with concrete and rigid is at a concrete/earth interface...in most areas the conduit will be gone in a year of so under that condition.
Don
 
I wish I had my code book handy. I always bury conduit 18" in the earth. I was wandering how a snow shovel could tear that up? I would just dig deeper and run pvc. I can not tell you how many rigid conduits I have replaced with pvc due to direct shorts from corroded rigid.
 
I would add that metal conduit tends to corrode at the soil line, so I'd tape about 1' of it, 6" above and below the soil/paving line
 
key words 344.10 B

key words 344.10 B

The key words are "where protected by corrosion protection" and the Galv. does that just fine. The painted enamel wont. GALV RMC will be there when the cows come home
 
I had to do A Military Spec Job once and they wanted all underground conduit to be Rigid with tar painted on it. That was a little extreme (and messy). Thank goodness for apprentices! :)
 
If money is not an object, Robroy or Ocal will protect the metal of the pipe, from extremely corrosive atmossperes (think pulp mills, and the like).
 
Rockyd said:
If money is not an object, Robroy or Ocal will protect the metal of the pipe, from extremely corrosive atmossperes (think pulp mills, and the like).
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That stuff is real fun to work with.
 
It's not that bad with hawged out shoes (bout 40 over), it's the threading part that usually turns ugly...
 
Old timers used fibered roof tar

Old timers used fibered roof tar

kpepin said:
I had to do A Military Spec Job once and they wanted all underground conduit to be Rigid with tar painted on it. That was a little extreme (and messy). Thank goodness for apprentices! :)
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Saw my dad paint fibered roof tar on galv RMC lots of times and they still use it on driveway culvert pipes at extra cost. I agree with post on why not pvc 24" deep could use sch *80 where entering and leaving ground level or slide over a piece of larger ridgid at the exit .
 
jetlag said:
The key words are "where protected by corrosion protection" and the Galv. does that just fine. The painted enamel wont. GALV RMC will be there when the cows come home
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That depends on the soil PH in the area you are working. Out here in the desert, we wrap all RMC in half lapped 10mil poly tape. Without that, it will be gone in short order due to soil PH. I realize this isn't an issue in most parts of the country, but it sure is here.
 
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