RHH and EMT Problems

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infinity

infinity

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Someone told me today that using the 2 hour fire rated, RHH conductors in EMT for fire-pump feeders has become problematic. Seems that the insulation is reacting with the EMT and corroding the inside of the conduit. Anyone hear of this? I've also been told that the cable will be losing it's listing by UL. All sounds somewhat suspect to me.
 
Thanks Bob, I vaguely remember that thread.

We were told today that we need to remove the over 600' of 2.5" EMT already installed up to the 17th floor of the building and replace it with concrete encased RMC. I suggested MI cable but they seem to want the RMC. :jawdrop:
 
There is a compatibility issue between zinc oxides and some types of rubber.The rubber tires on my boat trailer that are mounted on galvanized wheels is not an issue but I have had some rubber straps of a bungy cord have a reaction to the frame on the trailer so its just certain recipes,,,,,,,,,just citing my problems,,,,,,,this could be a serious finding but you would think this issue would have come to the forefront long ago.....:?:?:?:?

dick
 
dicklaxt said:
this could be a serious finding but you would think this issue would have come to the forefront long ago.....:?:?:?:?

dick
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Yes, to think that the first time you're hearing of a problem is when the product has lost it's rating altogether. Also think of new buildings where this stuff is already purchased and just now being installed, it won't pass a final inspection. :cry:
 
Thanks for the info Bob, it was an interesting read. Just pulled wires to a fire pump (RHH rated), and installed a lot of CI FA cable in past.
 
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iwire said:
I would have put money on RMC being also coated with zinc.
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I would say what they generally stock at the local supply house is (GRSC). And don't forget RMC comes in other metals too, e.g. aluminum. However, there are other steel types which may (or may not) have to be special ordered. Here's a snippet from steelconduit.org...

There are different processes used to provide corrosion protection to rigid steel conduit. Rigid steel conduit can have a primary coating of zinc, a combination of zinc and organic coatings, or a nonmetallic coating (such as PVC). Supplementary coatings can be applied to all three where additional corrosion protection is needed.

(NOTE: Contact manufacturers listed on the bottom of this page).


Rigid steel conduit is the heaviest-weight and thickest wall conduit. Where galvanized by the hot-dip process, it has a coating of zinc on both the inside and outside. Electro-galvanized rigid conduit has a coating of zinc on the exterior only, with approved corrosion resistant organic coatings on the interior. Rigid conduit with "alternate corrosion protection coatings" generally has organic coatings on both the exterior and the interior surfaces. Galvanized rigid metal conduit (GRC) is non-combustible and can be used indoors, outdoors, underground, concealed or exposed. Rigid steel conduit with coatings that are not zinc-based may have temperature limitations which will be noted on the manufacturer's product label and may not be listed for use in environmental air spaces; consult manufacturers’ listings and markings.
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The weird thing is that the same website says this about EMT...

Electrical Metallic Tubing (EMT), also commonly called thin-wall, is a listed steel raceway of circular cross section which is unthreaded, and nominally 10 feet long. Twenty foot lengths are also available. Covered by Article 358 of the NEC?, EMT is available in trade sizes 1/2 through 4. The outside is galvanized for corrosion protection and the inside has an approved corrosion resistant organic coating. EMT is installed by use of set-screw or compression-type couplings and connectors. It is permitted to have an integral coupling which is comprised of an expanded, "belled" shape of tube on one end with set screws. EMT with integral couplings is available in trade sizes 2 through 4.
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infinity said:
Thanks Bob, I vaguely remember that thread.

We were told today that we need to remove the over 600' of 2.5" EMT already installed up to the 17th floor of the building and replace it with concrete encased RMC. I suggested MI cable but they seem to want the RMC. :jawdrop:
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Was the EMT originally to be concrete encased???

If not, seems odd they'd switch to RMC and concrete encase.
 
Smart $ said:
Was the EMT originally to be concrete encased???

If not, seems odd they'd switch to RMC and concrete encase.
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Nope, just EMT and the 2 hour rated conductors. Seems like the only choices left are MI cable or RMC with 2" concrete encasement.
 
'Listed' is not exclusive to UL, there are other listing companies out there. If UL is pulling its listing of a certain item does not make it a code violation to install/use that item just because UL pulled their listing.
 
jusme123 said:
'Listed' is not exclusive to UL, there are other listing companies out there. If UL is pulling its listing of a certain item does not make it a code violation to install/use that item just because UL pulled their listing.
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It sounds like additional testing has shown these products do not meet the standard. The other NRTLs test to the same standards, so they should get the same results and also pull the listings.
 
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