"Moisture Proof Conduit"

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hdpaul1

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The title here may be well known and an old, "sore" subject to most electricians in the "real world". I would venture to guess that most electricians know that most conduit that is buried in the ground has water inside the conduit and that the purpose of conduit is for mechanical protection, not moisture prevention. Again, for the most part.

The issue, however, is beginning to gain momentum in the nuclear power, electrical generation realm and electrical engineers are being asked by the "regulator" (NRC) and other operations and maintenance personnel to address the long term effect of observed water found in conduits via manholes or trenches while digging, etc. on the ability of conductors to perform there intended function, safely and within the conductors "design" basis. I am not an engineer but believe that the issue is dialectric strength of wire immersed in water over a long term. My question to the engineers in the wire manufacturing industry or otherwise is "can you point to industry "white papers", or other technical articles on this subject. "

I would like to refer this data to the nuclear industry for consideration and further interpretation. Thank you for any and all technical input.
 
Any insulation with a "W" in its markings, ie;thwn, xhhw-2, is listed for wet locations. In

article 100, location,wet- subject to saturation with water or other liquids--. their efforts

would be better spent on the ' care taken installing the conductors ', this is all JIMO of

course I hold no degrees either. For practical purposes, on demo work pulling out under-

ground conductors that are soaking wet, are really in very good shape.
 
Moisture in buried conduit

Moisture in buried conduit

Benaround and Bobolectric,

Thanks for the replies. A bit more background. The nuclear industry is presently taking samples of underground cables that have been in buried conduits and sending to testing labs for evaluation. I'm not sure of the specifics of these tests except that they are more than visual examinations, to test the integretity of the conductors. The conductors are primarily feeder conductors form 480 volt to 4kv.
The article that sparked my interest is http://www.southwire.com/support/BuriedConduitChooseJktsThatResistMoisture.htm
I was wondering if there were some other white papers out there that would help to lead the way in helping to install the best type of conductor as well as some technical expertise in proper installation, beyond the obvious, to preclude damage during the actual installation.

Paul
 
Having worked in the industry since 1961, I?ve seen plenty of THWN, THW, and RHW that was in water and functioning fine just prior to being pulled out. It?s not the insulation they need to worry about, it?s the installation. Most wire failure is due to poor workmanship on the part of the installers.
 
Insulation

Insulation

If they are that worried about the ?Insulation? (I agree it is more of a Installation, quality of work, and the skill set or the workmen moreso than the insulation) However on their medium voltage gear, or even low voltage if you wanted to spend the money why not specify with partial discharge monitoring equipment to provide early warning of insulation breakdown prior to failure? And just curious is 4Kv a standard voltage for a nuclear facility? Why not 4160, 4800? (I have no experience with nuclear installation would love to however just curious)
 
hdpaul1 said:
The title here may be well known and an old, "sore" subject to most electricians in the "real world". I would venture to guess that most electricians know that most conduit that is buried in the ground has water inside the conduit and that the purpose of conduit is for mechanical protection, not moisture prevention. Again, for the most part.

The issue, however, is beginning to gain momentum in the nuclear power, electrical generation realm and electrical engineers are being asked by the "regulator" (NRC) and other operations and maintenance personnel to address the long term effect of observed water found in conduits via manholes or trenches while digging, etc. on the ability of conductors to perform there intended function, safely and within the conductors "design" basis. I am not an engineer but believe that the issue is dialectric strength of wire immersed in water over a long term. My question to the engineers in the wire manufacturing industry or otherwise is "can you point to industry "white papers", or other technical articles on this subject. "

I would like to refer this data to the nuclear industry for consideration and further interpretation. Thank you for any and all technical input.
Click to expand...
Your concern is valid. Wiring listed for W service is not suitable or tested for continuous submersion. That polymers are permeable to water was most dramatically demonstrated in the 70's when we discovered that latest-and-greatest MV insulation started failing, and the more water there was the higher the failure rate manifested. Only continuous metallic sheet can provide water protection as the 'ancients' of electricity had judged and installed lead covered cables. In today?s 'green' world, lead is a dirty word, so there is corrugated, continuously welded armor is available. Aluminum is common, but bronze has a higher corrosion resistance in common soil. Of course the armor integrity is vital for water resistance.

As the cable companies merge and diverse, many of the old names are vanished, however the research is still with the New parents. So your best bet is to approach them. With nuclear applications there is of course additional capabilities and concerns, so it would be a specialized and highly targeted research. I would not be surprised if there are some good papers on the other side of the Ocean. (I have a paper on a predictive testing of MV insulation failure in underground cable for example but it is more of a commercial introduction of a technology than a study. Search for UTILX on Google. I don't see a copyright notice on the paper, so you can PM me for it.)
 
I also have seen older conductors removed from raceways that were wet. The conductors looked fine to the naked eye. I have learned that the naked eye is only so good. The testing that can be performed on the conductors removed can go further than just meggering. Testing of the insulation and possible pitting/degredation of the copper can be anylised in a laboratory to get a real sense of what is occurring to the conductor over a period of time. I am interested to see what is found.
 
We have a line up of 4 compressors, installed in the mid 70s, each with a 4160v underground feed. One of the feeders failed in the mid 80s. On examination, after being pulled out of a water filled conduit, the wire was found to not be rated for wet locations. The remaining 3, fed with the same wire, have not experienced failure to this day. It?s the integrity of the outer jacket that counts.
 
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