Moisture Traps in Underground Conduits

[squeirdo]

NECA 111 for 2003 for the installation of non-metallic conduits in paragraph 4.1.m says, "Avoid moisture traps where possible. Where moisture traps are unavoidable, provide junction boxes with drain fittings at raceway low points." This statement has been incorporated into many project specs.

NEC 225.22 requires that raceways on exteriors of buildings shall be arranged to drain, and NEC 230.52 says that where exposed to the weather, raceways enclosing service entrance conductors shall be suitable for a wet location and arranged to drain. NEC 314.15 says that in damp or wet locations, boxes shall be placed or equipped so as to prevent moisture from entering or accumulating within the box and permits this installation of 1/4" or smaller drain holes or listed fittings.

The NEC references seem to apply to above ground installations. Is it correct to interpret NECA 111 4.1.m as applying to underground installations? Does it seem reasonable to require the installation of a junction box with a drain fitting in all underground conduit runs with 90s at both ends? In addition, would this NECA requirement justify requiring all underground conduits to be arranged to drain to junction boxes that aren't shown on the plans?

 

[mopowr steve]

And just how do you expect to drain water from underground conduits? You must have a hole at the lowest point along conduit run to drain, but guess what; when water table rises it will use that same drain hole to fill conduit with water. That is why conductors in underground conduits must be listed for wet conditions.

 

[480sparky]

........ Does it seem reasonable to require the installation of a junction box with a drain fitting in all underground conduit runs with 90s at both ends?.......

And how would one access this box, especially when you're required by job specs to install the conduits deeper than normal, like 48" or even 60"? And what about runs between light poles in a paved parking lot?

 

[don_resqcapt19]

It is not really possible to keep the water out of underground raceways in most cases, unless you have manholes. However the conductors seem to last longer if you can arrange the raceways to drain. This is an even bigger issue where the raceway is rigid steel or concrete encased and not installed below the frost line. The crushing force of the ice damages the insulation. This has also been a problem with underground fiber optic installation and Polywater has an antifreeze product that you can inject into the raceway to prevent the ice damage.

Industrial installations with manholes often have the raceways arranged to drain to the manholes and often there are sump pumps installed in the manholes.

 

[kwired]

In locations where temps get below freezing - above ground raceways that have accumulated water in them break open when it freezes. I guess they will drain after thawing once that happens though.

Underground, they will not freeze below frost line, above frost line - I guess they would drain as well if they break open.

Underground raceway, unless you are in a high water table location, the water that accumulates is usually from condensation, sealing the ends of the raceway will help reduce condensation effects, but at same time once moisture is in the raceway it is not going to leave unless you provide a means to drain it or a means to heat it so it evaporates, which a seal would inhibit getting rid of water vapor.

Any way you look at underground in a raceway water is very likely to be expected there in most situations.

 

[squeirdo]

Thank you for the input. We'll see how this plays out.

 

[don_resqcapt19]

It is not an approved method, but at my house I had an issue with my underground phone line. It was PVC under ground with a rigid risers at the pole and at the house. The raceway got water in it and the freeze thaw cycles the first winter stretched the cable until is physically separated. We ran a temporary cable on the ground for the rest of the winter. The next spring I pulled out the cable to find out what the problem was...the cable came out of the pipe in two pieces. The cable that was physically pulled apart was the standard 3 pair phone cable with the metallic gopher shield...it takes a lot tension to break that cable but the ice did.

I dug up the 90s at each end and drilled drain holes through the conduit and replaced the cable...that was about 30 years ago and the cable still works.