Underground conduit and pull-box questions

Discussion in 'Electrical Forum discussion & Blog' started by charp, Oct 2, 2011.

  1. charp

    charp New Member

    Messages:
    19
    Location:
    Grass Valley, CA
    Can the service conductors, neutral and ground be run in the same conduit?
    What is the minimum radius for bends in 3" conduit with 4/0 aluminum service conductor?
    Any pictures or diagram of a pull-box? What keeps the conduits from filling with water? How close to the lid are the conductors?

    Thanks
  2. jwelectric

    jwelectric Electrical Contractor/Instructor

    Messages:
    2,534
    Location:
    North Carolina
    All conductors of the same circuit must be in the same conduit. There is no way to keep water out of conduit either underground or on the surface. Google underground boxes and you will find there are thousands of them.
  3. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,642
    Location:
    Cave Creek, Arizona
    quote; There is no way to keep water out of conduit either underground or on the surface.

    Really? You mean it is IMPOSSIBLE? Then all those sealing methods used to do it are useless? Seems like people have been doing a lot of wasted effort in that case. Or maybe you are not fastening the pipes together tightly. IF you purchase your elbows, they will have the proper radius, however you can also get longer radius bends if you wish to have an easier time with the pull and have the space.
    Last edited: Oct 3, 2011
  4. nukeman

    nukeman Nuclear Engineer

    Messages:
    711
    Location:
    VA
    I think jw is talking about condensation and that conduit is considered a "wet location" and the wiring used needs to be rated as such.
  5. jwelectric

    jwelectric Electrical Contractor/Instructor

    Messages:
    2,534
    Location:
    North Carolina
    Typical question from a plumber and I have one that most plumbers hesitate when asked. Are plumbing pipes designed to keep water in or out?

    No pipe weather plumbing or electrical will keep water out. Seals are installed to slow the mitigation of gases not water in an electrical system. I seal one end or the other for a pipe entering an underground installation to keep methane from entering the enclosure not to keep water out where pipe is installed with direct burial conductors.
    Sealing compound is used when going from a cold to hot environment to keep condensation down. We don’t use check valves and flow meters in electrical wiring.
  6. ballvalve

    ballvalve General Engineering Contractor

    Messages:
    3,261
    Location:
    northfork, california
    Most conduit I cut into is water filled. I have run pump wires INSIDE the drop pipe.
  7. charp

    charp New Member

    Messages:
    19
    Location:
    Grass Valley, CA
    Googling results in all kinds of random images, not many that are helpful! I talked to a commercial electrician today so now I know what to do. I had to locate the existing underground conduit which I eventually found with a digging bar, the resulting crack in the 2" ABS conduit produced a 6" mini geyser. Is it a good idea to run a drain to daylight and/or spray some expanding foam into the end of the conduit that will go under the house to the panel?
    Last edited: Oct 3, 2011
  8. ActionDave

    ActionDave Electrician

    Messages:
    346
    Location:
    Colorado
    I would not run a drain. I would make a weep hole in the lowest section.

    Spray foam does not hurt, but as has been said you will never have a water proof conduit.
  9. jwelectric

    jwelectric Electrical Contractor/Instructor

    Messages:
    2,534
    Location:
    North Carolina
    Never and I repeat never use spray foam in conduit use Duck Seal only.

    There is no such thing as ABS concuit.

    Edited to add

    Anything you put around electrical conductors or cables must be listed for the purpose or application. I have seen caulking installed in conduit supplying walk-in coolers that destroyed the insulation on the conductors resulting in a fault situation.
    Last edited: Oct 4, 2011
  10. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,642
    Location:
    Cave Creek, Arizona
    Condenstion comes from moist air being "chilled". IF there is NOT air movement in the conduit, there can be NO condensation. I have installed MANY conduits which did NOT fill with water. And since ONLY "W" rated conductors are "wet", the wires in a "flooded conduit" would have to be THWN or similar.
    Last edited: Oct 4, 2011
  11. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,017
    Location:
    New England
    Living in the desert is different than situations where the water table is near the surface.
  12. charp

    charp New Member

    Messages:
    19
    Location:
    Grass Valley, CA
    "There is no such thing as ABS concuit"

    All I know is that the plastic conduit is black. I guess it could be poly pipe? It was installed in the late 1970s. Also, the ground is in it's own smaller diameter black conduit.

    Is there a minimum depth for the service conductor inside the "Christy" box?
    Last edited: Oct 4, 2011
  13. jwelectric

    jwelectric Electrical Contractor/Instructor

    Messages:
    2,534
    Location:
    North Carolina
    There is not now nor has there ever been ABS (black) conduit. The grounding conductor is required to be installed in the same raceway as the ungrounded conductors.

    If you are doing all this because there is a split in the black pipe, don’t waste your time and money. Leave it alone.
  14. Jim Port

    Jim Port Electrical Contractor

    Messages:
    156
    Location:
    Maryland
    The black ABS pipe was for plumbing, not for use as an electrical conduit.
  15. ballvalve

    ballvalve General Engineering Contractor

    Messages:
    3,261
    Location:
    northfork, california
    When some clown puts wires in an abs pipe it becomes conduit.
  16. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,642
    Location:
    Cave Creek, Arizona
    And when they use gray PVC conduit in a plumbing system it becomes a water or drain line. I was also referring to when I was in Chicago and Michigan.
  17. jwelectric

    jwelectric Electrical Contractor/Instructor

    Messages:
    2,534
    Location:
    North Carolina
    No, it is still a plumbing pipe with electrical conductors and an illegal installation
  18. charp

    charp New Member

    Messages:
    19
    Location:
    Grass Valley, CA
    I'm not doing this because of the broken conduit/pipe. It's in the way of excavating I'm doing next to and behind the garage to create level parking and vehicle storage so my stuff is parked outta sight and not right in front of the garage. Pretty much everything on this property needs to be redone.

    So, when the wire comes into the pull box and then out in the conduit going under the house how deep does it need to be in the pull box? I was told that the conduit should angle up at 45 degrees so the the wire clears the lip of the box when pulling it.

    Thanks
  19. jwelectric

    jwelectric Electrical Contractor/Instructor

    Messages:
    2,534
    Location:
    North Carolina
    No less than 24 inches but most service conductors are 36 inches deep.
    Bring the conductors out of the pull box using a 90 degree bend not a 45.

    The splice must be an underground splice and can be made without the box
    300.5(E) Splices and Taps. Direct-buried conductors or cables shall be permitted to be spliced or tapped without the use of splice boxes. The splices or taps shall be made in accordance with 110.14(B).

    EDITED TO ADD:

    As I was entering mile three on the treadmill I had a thought, if the service is at the street then these conductors are not service conductors but feeders and are without a doubt under the NEC.

    This means that when the inspector looks at them they will have to be in PVC and not ABS. You may be opening a can of worms that will end up costing a lot of money.
    Last edited: Oct 6, 2011
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