Conduit underwater

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DEW202001

DEW202001

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ODENTON, MD
I am a inspector at a water treatment pant and there is a new UV tank/system being installed.The electrical contractor installed a 3" conduit under the concrete slab that goes to the UV control panel. With it being under the slab it will be in the water flow of the UV. I am not a big fan of it being installed in the water flow but I can't find any code issue with it. I looked in article 682 but it does not really apply. Any fees back would be great.


FYI
The conduit was going to be in slab but because of the size
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of conduit and thickness of slab the engineer thought it would not work structurally.
 
What's the conduit made out of? I'm assuming the UV is treating"finished" water directly before it goes into the distribution system? If it's near the head of the plant the alum will eat metal conduit up in no time. Water chemistry can be very corrosive in water treatment. I'd be pretty uncomfortable with it. When the conduit fails will it act as a pipe to flood the MCC/ electrical room?
 
Saturn_Europa said:
...Water chemistry can be very corrosive in water treatment. I'd be pretty uncomfortable with it. When the conduit fails will it act as a pipe to flood the MCC/ electrical room?
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Having experienced this exact failure when a conduit was installed in a cooling canal, I can attest this is a terrible idea. When the conduit inevitably breached, the canal began draining directly into the electrical room.

I don't think any carbon steel or aluminum can be adequately protected for long-term submersion. It's a case of when, not if it fails.
 
big john said:
Having experienced this exact failure when a conduit was installed in a cooling canal, I can attest this is a terrible idea. When the conduit inevitably breached, the canal began draining directly into the electrical room.

I don't think any carbon steel or aluminum can be adequately protected for long-term submersion. It's a case of when, not if it fails.
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You could improve your odds by using stainless steel conduit and fittings. Calbrite is one supplier. However, if there is elevated chlorides in the water you might see chloride stress crack corrosion. If they inject downstream, you might be OK.
 
So I was thinking of the conductors not the leaks that could let water into other areas. I agree water finds a way in.

So while I agree that could be a problem I am really curious what NEC section prohibits this. I don't think there is one so bad design or not it should pass inspection.
 
Saturn_Europa said:
What's the conduit made out of? I'm assuming the UV is treating"finished" water directly before it goes into the distribution system? If it's near the head of the plant the alum will eat metal conduit up in no time. Water chemistry can be very corrosive in water treatment. I'd be pretty uncomfortable with it. When the conduit fails will it act as a pipe to flood the MCC/ electrical room?
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It's PVC coated conduit


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DEW202001 said:
It's PVC coated conduit


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Depending on how corrosive the water is and if there are any nicks in the PVC jacket (there usually are) the installation could last from 5-20 years. Impossible to predict. But if its anything like my plant it will fail 1 month after the 12 month warranty has expired.

Please post back with how this turns out. I was somewhat involved in situations like these when they were building my plant. We (the owner) would point out something that was poorly designed or did not meet code to our engineering construction manager. They would point it to the contractor, the contractor would point back to the original design or spec. It would land in the design engineers lap. They would draw up a shop drawing correction (for free), hand it to the engineering construction manager, they would forward it to the contractor, the contractor would take a look at it, estimate a price plus profit then hand the owner (us) a huge bill.
 
iwire said:
Still wondering what code section you are citing to require a change to that conduit.
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Possibly under some general fitness for use clause; I've never seen anything explicit that covers this situation. In the end I'd say it's a design issue, and we know the NEC isn't intended to be a design guide.
 
Section 300.8 and its myriad Subsections discuss the general requirements for protection from corrosion and deterioration. It isn't particularly specific about how to do it but it is very specific that it must be done.
 
rbalex said:
Section 300.8 and its myriad Subsections discuss the general requirements for protection from corrosion and deterioration. It isn't particularly specific about how to do it but it is very specific that it must be done.
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Ok so at what point does one decide they have sufficiently mitigated corrosion?
To what level?
To what end?
 
Sierrasparky said:
Ok so at what point does one decide they have sufficiently mitigated corrosion?
To what level?
To what end?
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This is definitely a case where the Code is not a design standard or intended as an instruction manual.

I had the great good fortune in my early career to be mentored by several very experienced engineers. Eventually, I began to recognize where problems were likely. I also had access to metallurgists and structural engineers that I counted on to steer me in the right direction. I recognize not everyone has immediate access to those resources. However, most electricians, engineers, etc. have far more resources available than they realize. This thread is a pretty good example. It may take some judgment to recognize where to apply it.
 
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