RMC Direct Burial

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euclid43

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I just failed an dwelling (no traffic- walkway) underground inspection because inspector said that my RMC 12" underground would corrode. As part of my demeanor, I said I will put tar around 30 feet of 1-1/2 RMC. I've never failed with this installation before. Should I stand by my experience or show him the code? Thanks
 
@euclid43

Did the inspector cite a code reference? Are you located in Nevada or other areas of the country where the AHJ and Locality has local rules for supplementary corrosion protection?

RMC already has protection as part of the evaluation process. Unless their is some local requirement I would visit www.steeltubeinstitute.org and view their Q & A Area. Here is an excerpt from that site below. Note: The below information is openly posted and available at the aforementioned website above.

"The 2011 National Electrical Code (NEC) allows the direct burial of all three products as noted in their respective Articles:Galvanized Steel RMC Section 344.10 (B) Corrosion Environments. Galvanized steel RMC, elbows, couplings, and fittings ?shall be permitted to be installed in concrete, in direct contact with the earth, or in areas subject to severe corrosive influences where protected by corrosion protection and judged suitable for the condition.?

IMC Section 342.10 (B) Corrosion Environments. Galvanized steel IMC, elbows, couplings, and fittings ?shall be permitted to be installed in concrete, in direct contact with the earth, or in areas subject to severe corrosive influences where protected by corrosion protection and judged suitable for the condition.?

EMT Section 358.10 (B) Corrosion Protection. Galvanized steel EMT, elbows, couplings, and fittings ?shall be permitted to be installed in concrete, in direct contact with the earth, or in areas subject to severe corrosive influences where protected by corrosion protection and approved as suitable for the condition.?

Members of the Conduit Committee of the Steel Tube Institute apply a zinc coating to galvanize steel RMC, IMC and EMT. Therefore, these products are ?protected by corrosion protection? as the Code requires. However, in severe corrosive environments, the designer or AHJ may decide to require additional or supplementary protection.

Underwriters Laboratories? Guide Information for Electrical Equipment ? The White Book 2011 contains information relating to limitations or special conditions applying to products listed by UL. The Directory states that Galvanized steel RMC and IMC do not generally require supplementary corrosion protection when installed in soil unless: 1. Soil resistivity is less than 2000 ohm-centimeters. 2. Local experience has confirmed that the soil is extremely corrosive.

(Note: Soils producing severe corrosive effects have low electrical resistivity, expressed in ohm-centimeters. Local electric utilities commonly measure the resistivity of soils. The authority having jurisdiction (AHJ) has the authority to determine the necessity for additional protection.) EMT in direct contact with the soil generally requires supplementary corrosion protection. However, local experience in some areas of the country has shown this to be unnecessary."

Hope this was helpful.
 
euclid43 said:
I just failed an dwelling (no traffic- walkway) underground inspection because inspector said that my RMC 12" underground would corrode. As part of my demeanor, I said I will put tar around 30 feet of 1-1/2 RMC. I've never failed with this installation before. Should I stand by my experience or show him the code? Thanks
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Unless it is plastic coated, it will corrode, it is just a matter of how fast and how long it is expected to last.
As long as you are not using the RMC as the EGC and are not planning to pull more wires into the same pipe in the distant future the disintegration of the pipe may not be a practical problem.

The nature (acid/alkaline) and moisture content of the soil will have an effect too.
 
MasterTheNEC said:
@euclid43

Did the inspector cite a code reference? Are you located in Nevada or other areas of the country where the AHJ and Locality has local rules for supplementary corrosion protection?
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Yep...having a location on the OP's profile may assist as well. However, at the end of the day I would like a code reference to support the local inspectors decision and proof that the soil meets "severe" corrosive conditions. Many areas of the country that's well established and in others not so much. While we know everything will corrode in time and we know that the zinc coating is sacrificial to the steel...it is still permitted by code to use and personal feelings are left on the bench for the second string:)

Just my two cents !
 
darekelec said:
Around here inspectros ask to run egc inside because they know rmc is gonna corrode
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Ask or Insist?

Are they playing inspector or expector during their 8 hour shift?

Hey at least they are letting you run the RMC at that point....and putting more conductors in the raceway helps feed the wiring manufacturers children..so have at it:lol:
 
Generally the worst corrosion is the first few inches below emergence from the surface, as this is the only point that is both in contact with any corrosive agent in the soil as well as being exposed to oxygen. Type of soil, corrosive agents present, moisture present can make some difference but I find this to be the general rule.
 
kwired said:
Generally the worst corrosion is the first few inches below emergence from the surface, as this is the only point that is both in contact with any corrosive agent in the soil as well as being exposed to oxygen. Type of soil, corrosive agents present, moisture present can make some difference but I find this to be the general rule.
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And just to add some information. The manufacturers of Steel Conduit and tubing do recommend adding the supplementary protection ( above what is already on the product) for those transition points to the tune of 6 inches in either direction.
 
darekelec said:
Salt at walkways and dogs pee i noticed contributes to corrosion a lot.
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That's some NUCLEAR dog pee if it gets down to where a buried conduit is located. But alas ..check out the website I posted earlier as it has some great info. (like I am a salesman or something, umm...trust me I am not:eek:)
 
MasterTheNEC said:
That's some NUCLEAR dog pee if it gets down to where a buried conduit is located. But alas ..check out the website I posted earlier as it has some great info. (like I am a salesman or something, umm...trust me I am not:eek:)
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Exactly, goes back to what I said before, only short distance below point of emergence is usually exposed to anything that will cause significant corrosion. If the raceway emerges from a surface that gets snow melt treatment - you may see some increased corrosion near the point of emergence - the rest is probably fine. Same with the dog pee, or any other animal for that matter.
 
kwired said:
Exactly, goes back to what I said before, only short distance below point of emergence is usually exposed to anything that will cause significant corrosion. If the raceway emerges from a surface that gets snow melt treatment - you may see some increased corrosion near the point of emergence - the rest is probably fine. Same with the dog pee, or any other animal for that matter.
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lol....in reading some of the posts on here today I am also thinking that our members invest in "Meteor Shower" Insurance also just in case it happens. It's like Hail Damage coverage only out of this worldly cheap.
 
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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Dog pee is mostly for conduit entering to underground. Imagine it to be like a fire hydrant. Especially in subway elec systems.


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Sorry...my dog has more respect for conduit ( it's an electricians dog- go figure) he still uses a fire hydrant. Yes, he is anti public service.
 
MasterTheNEC said:
lol....in reading some of the posts on here today I am also thinking that our members invest in "Meteor Shower" Insurance also just in case it happens. It's like Hail Damage coverage only out of this worldly cheap.
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How wide are the doorways in your home?
 
euclid43 said:
I just failed an dwelling (no traffic- walkway) underground inspection because inspector said that my RMC 12" underground would corrode. As part of my demeanor, I said I will put tar around 30 feet of 1-1/2 RMC. I've never failed with this installation before. Should I stand by my experience or show him the code? Thanks
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I would ask him for a code reference to substantiate his citation...
 
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