water in buried conduit question
- Thread starter toleary
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zbang
Senior Member
- Location
- Roughly 5346 miles from Earls Court
How big is the pipe? Get the water out then pull a swab through. Tape up the ends of the cables and pull. Might want to chop off the first foot of each in case some water got in under the tape and into the jacket. Are you using cable rated for wet environments? I'd use direct-burial cable if available.
Don't worry about more water finding it's way back into the pipe, it will.
Don't worry about more water finding it's way back into the pipe, it will.
jumper
Senior Member
- Location
- 3 Hr 2 Min from Winged Horses
Are your cables rated for wet locations? If so, no prob.
hbiss
EC, Westchester, New York NEC: 2014
- Location
- Hawthorne, New York NEC: 2014
- Occupation
- EC
Yes and there is no way to keep water out. Buried conduit is classified as a wet location. Use cable suitable for direct burial and it won't be a problem.
-Hal
- Location
- Illinois
- Occupation
- retired electrician
The biggest danger to the condutors in water in conduits, around here, is when the water freezes and crushes the conductors. This often damages the insulation and or jacket and conductor failure will follow.
- Location
- New Jersey
- Occupation
- Journeyman Electrician
Is there a NEC requirement for these cables to rated for wet locations?
jumper
Senior Member
- Location
- 3 Hr 2 Min from Winged Horses
310.10(C) would apply I believe.
how deep are you burying the conduit?
- Location
- Illinois
- Occupation
- retired electrician
It would almost never be below the frost line of about 48", and even if it was, there is often water in the riser at each end that will be well above the frost line.
- Location
- Illinois
- Occupation
- retired electrician
Does that rule apply to conductors installed per the rules in the Chapter 7 and 8 articles?
hbiss
EC, Westchester, New York NEC: 2014
- Location
- Hawthorne, New York NEC: 2014
- Occupation
- EC
No. LV and communications (725 & 800) are separate from Chapter 3. The only time anything from Chaper 3 is applicable is when it is specifically referred to.
No. You can use anything you want. But if you want it to last...
I don't think I've ever seen that happen, how many pole risers have you seen do that? Maybe it's because of improper cable? I know I've seen indoor cable jacket shatter like glass at moderately low temps. Direct burial cable is pretty tough, stays flexible and the flooding compound keeps small problems from becoming large if the jacket should become damaged.
-Hal
jumper
Senior Member
- Location
- 3 Hr 2 Min from Winged Horses
Chapter 8, no. Chapter 7 Article 725, yes ( I think).
725.3 Other Articles. Circuits and equipment shall comply
with the articles or sections listed in 725.3(A) through
(J). Only those sections of Article 300 referenced in this
article shall apply to Class 1, Class 2, and Class 3 circuits.
90.3 Code Arrangement. This Code is divided into the
introduction and nine chapters, as shown in Figure 90.3.
Chapters 1, 2, 3, and 4 apply generally; Chapters 5, 6, and
7 apply to special occupancies, special equipment, or other
special conditions. These latter chapters supplement or modify
the general rules. Chapters 1 through 4 apply except as
amended by Chapters 5, 6, and 7 for the particular conditions.
Chapter 8 covers communications systems and is not subject
to the requirements of Chapters 1 through 7 except where
the requirements are specifically referenced in Chapter 8.
- Location
- Illinois
- Occupation
- retired electrician
The damage I have seen has not really been in the risers, but I have seen water in risers, so there is no reason that it can't happen in the riser.
I've seen it many times with parking lot lights that were in rigid conduit, a couple of times with fiber in rigid conduit, and at my house with the underground phone cable in PVC conduit.
In my case the standard underground phone cable with the metal gopher shield was install in 3/4 PVC for about 80' from the alley pole to my house. The freezing and thawing and re-freezing action actuall pulled the cable appart. I had a cable on the ground until the next spring. When I pulled the cable out from the LB at the house, I got about 3' and you could tell that the cable had been broken by excessive tension. I dug the conduit up and drilled some holes in it and pulled in a new phone cable...that was over 20 years ago and it has never happened again.
With the fiber, the glass was broken. In doing some research on that, there is a product made by Polywater that you pump into the raceway to prevent the problem.
With the parking lot conductors the freezing and thawing of the water in rigid or concrete encased PCV crushes the insulation and at some point does enough damge that the insulation fails.
zbang
Senior Member
- Location
- Roughly 5346 miles from Earls Court
Even without the freeze/thaw cycles, I've seen PVC jacket communications cable basically self-destruct when soaked in ground water for a couple of years. Granted, it was low-bid cable, but still. Had better luck with teflon plenum cable underground, but that was a while ago.
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