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#60514 - 01/04/06 05:12 PM Pipe dope on rigid, Good idea?  
bot540  Offline
Joined: Sep 2004
Posts: 174
Vernon Hills, IL
I was thinking about putting pipe dope on the last 1/4" of threads on some 1/2 rigid pipe going in the ground. My thinking was that this will help keep water out making the installation last longer.
Do you think this would be in violation of 250.4 or other code. The rmc still has continuity, especially since the sealant is only on the ends of the threads. I will also be pulling in a ground wire.

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#60515 - 01/04/06 07:03 PM Re: Pipe dope on rigid, Good idea?  
resqcapt19  Offline
Joined: Nov 2000
Posts: 2,148
If these are field cut threads, then 300.6(A) requires that the threads the threads be coated with an approved electrically conductive, corrosion-resistant compound.
I don't think that pipe dope will help seal conduit joints. Pipe dope is not really intended to be a sealant. It is a lubricant that permits you to tighten plumbing pipe tight enough so that the metal to metal contact makes a seal. This works on plumbing pipe because both the male and female threads are tapered threads. This will not work on conduit because only the male threads are tapered and you cannot achieve the metal to metal contact required to prevent leaks.
Even if you could make a tight seal at a conduit joint, the conduit will still fill with water. As the temperature and other environmental conditions change. Over time water vapor in the air will condensate into liquid water in the raceway.


#60516 - 01/04/06 08:21 PM Re: Pipe dope on rigid, Good idea?  
Radar  Offline
Joined: Apr 2004
Posts: 349
Los Angeles, CA
It's actually related to Relativity - and to Murphey's law: The more you try to keep water out of underground conduit runs, the more likely it is that water will eventually get in.

OK - I'm only kidding about Relativity, but there is some similarity.


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#60517 - 01/04/06 08:33 PM Re: Pipe dope on rigid, Good idea?  
renosteinke  Offline
Cat Servant
Joined: Jan 2005
Posts: 5,316
Blue Collar Country
Plumbers use pipe dope; electricians do not.

Part of the reason is that we need more than continuity; we need a ground path. And, part of the reason is that our threads were never intended to be water or air tight. (Notice how many fittings have straight, and not tapered, threads?)

If you want to ease the assembly, might I suggest either a listed material, such as "Noalox" and "Penetrox," or even anti-seize compound? These will also help prevent the pieces from rusting together.

Otherwise, when completed the cut threads ought to be coated with one of those spray-on zinc compounds. Or wrapped in pipe wrap tape. Or both.

#60518 - 01/05/06 03:47 AM Re: Pipe dope on rigid, Good idea?  
e57  Offline
Joined: May 2003
Posts: 2,876
Penetrox, Corrosion X HD, etc on the threads themselves, and made up tight, REAL TIGHT. Thats enough for average underground soil conditions, for saturated soil conditions I offer this suggestion; mate the pipe up tight... Finish the installation. Then a good tight and smooth taping of the whole joint with pipe wrap, or before burial, a good liberal coating or Sicaflex, or Fire and Ice roof patch (The stuff used on membrane roofs), and wait until dry before burial, either method is just an encasemnet of the electrically complete joint, not part of the joint. Niether will do anything to keep the rest of the pipe from rotting if the ph level of the soil with corrode the pipe anyway. There is PVC coated RMC you could use for that, and they have special sleeves and compounds that do this. Then RNC if you can use that...

Mark Heller
"Well - I oughta....." -Jackie Gleason

#60519 - 01/05/06 07:06 AM Re: Pipe dope on rigid, Good idea?  
resqcapt19  Offline
Joined: Nov 2000
Posts: 2,148
Even when you do all of that, the conduit will still fill with water, so why do all of that extra work?


#60520 - 01/05/06 08:58 PM Re: Pipe dope on rigid, Good idea?  
e57  Offline
Joined: May 2003
Posts: 2,876
I've had pretty good luck that way. Also not talking 'bout condensation, "saturation", i.e. ground water.... Sometimes even shallow trenches here will be below water table. (Like my back yard this time of year, <6"... My cross street is Agua way, named for the creek that used to be there... [Linked Image] A tributary runs through my garage. There is also water coming from my lawn, until about a month after rainy season ends.) This time of year, I have at times had to make the pipe up above the trench, and drop it into 6" of water at the bottom of the trench. Otherwise, it may as well be plumbing... I have had some that act as french drains if running down hill.

Mark Heller
"Well - I oughta....." -Jackie Gleason

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