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#103308 06/25/02 06:42 PM
Joined: Oct 2000
Posts: 2,749
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[Linked Image]

This picture was taken in Las Vegas last month, and shows were the conduits are corroded at the point of contact with the earth.

They were wrapped with tape, but it looked like there was not enough provided.

This is a common situation around the country, and could use a technical reply from someone who may know the reasons why this happens?

I will also search for that information in the UL Directory "White Book" and add comments later.

[This message has been edited by Joe Tedesco (edited 06-25-2002).]


Joe Tedesco, NEC Consultant
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#103309 06/25/02 09:44 PM
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I don’t think they salt roads or alleyways in Vegas—at least not very often.

Some years ago this was discussed in EC&M Magazine. With galvanized, It is a potential problem at the transition between air and soil; soil and concrete; and concrete and air. Worse yet is bare aluminum conduit in concrete—it turns to powder.

#103310 06/25/02 10:32 PM
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This is old fashoned corrision. It is not something that can be stopped - slowed down- but not stopped. The service taught that a galvanic cell simular to a battery- anode-cathode,elecrolite, and path for current flow will return any metal back to it's natural state.
Dissimular metals some of those are in the ground (different than the conduit) set up the anode vs cathode, contact with earth= current path,water = electrolite, together = galvanic corrision cell.
This is the reason I use PVC as much as possible in earth or concrete.

I saw some DOD web sites that had some good info on this, but don't have those URLs anymore.


ed
#103311 06/26/02 08:39 PM
Joined: Apr 2002
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Had this situation a few times, made a determination that the corrosion started at a section that was field threaded. Another opinion we heard was "poor drainage" as may be evidenced by the pipe that resembles a downspout/roof drain near the corroded conduits. Question please; what type of "tape" was/is evident at the base area of the conduits??

We solve the situation with either PVC or PVC coated GRC if necessary.

John

[This message has been edited by HotLine1 (edited 06-26-2002).]


John
#103312 06/26/02 10:24 PM
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Joe Tedesco, NEC Consultant

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