water proofing inside PVC conduits

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1beefstu

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I am afraid of water getting into the underground conduits and then leaking out inside a $5,000,000.00 home.

I have several underground conduits that penetrate a basement wall foundation and then continue into the joist spaces of the living areas.

Is there anyway to install a waterproof barrier inside the conduits just before they enter the home?

I have 3 2.5" conduits with 3 4/0 THHN conductors and 1 #2 THHN ground wire that need to be sealed inside the electrical PVC conduit.
 
1beefstu said:
I am afraid of water getting into the underground conduits and then leaking out inside a $5,000,000.00 home.

I have several underground conduits that penetrate a basement wall foundation and then continue into the joist spaces of the living areas.

Is there anyway to install a waterproof barrier inside the conduits just before they enter the home?

I have 3 2.5" conduits with 3 4/0 THHN conductors and 1 #2 THHN ground wire that need to be sealed inside the electrical PVC conduit.
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I would slope the pipe away from the house , if possible, and also use duct seal or spray foam sealant. Make sure the sealant is not harmful to the conductors.
 
water proofing inside PVC conduits

Dennis Alwon said:
I would slope the pipe away from the house , if possible, and also use duct seal or spray foam sealant. Make sure the sealant is not harmful to the conductors.
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What sealant would recommend?
Conduits are areasy installed and the slope was not considered.
 
I would also try the Polywater product.
You would also want to make sure that there won't be any leaks around the outside of the pipes.
 
Slope is not relevant. Sloping away from the house would only increase the quantity of water stored in the PVC until leakage occurs. Total burial depth would determine how much pressure you have to withstand. At 4 feet below grade, or at least below the highest point where water can enter, the seal would have to withstand 1.72 psi (4 ft x 0.43 pounds per square inch per foot). You should assume that eventually the entire conduit will be filled (you are eliminating the most convenient drain) and the maximum height of water in the conduit will determine the final pressure.

Your 2.5" conduit has an area about 5 square inches, although that will be decreased by the area of the wire present. Worst case, at 4 ft., would be about 8 pounds total pressure on the seal. Not a lot, but not insignificant.

Sorry I didn't answer your question: what to use?
 
sgunsel said:
Slope is not relevant. Sloping away from the house would only increase the quantity of water stored in the PVC until leakage occurs.
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I am not so sure it is not relevant at all. If there is water from condensation I would think it would take a tremendous amount of water to get into a building. It would also depend on how the conduit was dealt with on the other end.

If there is a leak and ground water is getting in then the water would also be able to ooze out.
 
Eventually the conduit will fill with water unless you completely seal ALL openings (not always so easy) or provide a drain. If the conduit is underground, any leakage will likely be into the conduit. It sounds like the lowest point to act as a drain is the entrance into the basement. If the entrance into the building is not sealed, any water entering the conduit will enter the house. If sloped downward away from the house, it will only take longer. There won't be much evaporation inside of a conduit.

Of course, this will probably not be an issue in Arizona or other desert areas. In most areas, however, it can be surprising how much water will condense from air.
 
petersonra said:
IMO, best bet is to install some kind of drain.
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Good idea, and where would it drain to....?

There are to known ways to avoid the potential of water-leak. One is to have a continuous 'conduit', the other is, in the case of PVC pipes to seal every joint, and pressure test it. To avoid condensate buildup critical conduits in some cases are pressurized with an inert gas and the pressure is monitored. (Not neccessarily a useful solution for your application.)

If the conductors are not yet installed, or if they can be pulled/re-pulled, you may want to consult companies specializing in water-piping restoration where they inject and pressurize the pipes with a solution that seals every weep points and forms a pressure rated barrier along the entire length of the pipe. Again, this is an out-of-box idea, but it depends how badly want to keep water out and how likely that this is a realistic problem in the first place.
 
I kind of had in mind drilling a hole in the conduit at its lowest point and directing a small tube to a sump. Nothing real elaborate.
 
stevenje said:
If it is possible in your conduit run, set an underground pull box set on a bed of gravel so it will drain.
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or put inverted T's at a point just outside the basement, with a fine mesh screen covering the opening to stop insects.

I vary rarely breach a basement wall just because of this and the liability that comes with it, if I have to come into a basement I will pop up out of the ground and LB into the wall above ground.
 
1beefstu said:
...

I have several underground conduits that penetrate a basement wall foundation and then continue into the joist spaces of the living areas.

...
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Typically first-level joists are set on top of basement foundation walls, above grade... and typically (outside) underground conduits are turned up, change elevation on the outside of the foundation wall, then penetrate the band board with an LB to run in joist spaces.

Is there some reason for a change from the standard approach or is the structural design atypical... or is it the owners simply not wanting to see conduits on the outside of their rather expensive home???

Just a thought, and working with the routing you have put forth, perhaps put a tee outside at the point of penetration, bush it down to say 3/4" or 1/2" and run that size down to the footer where there may be footer drainage system (depends on location; ask first before digging; backfill with sand). Should keep the conduits drained in all cases but flooding at a height above the horizontal conduit run.
 
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