Transition from conduit to romex.

Discussion in 'Electrical Forum discussion & Blog' started by remster, Jun 17, 2007.

  1. remster

    remster New Member

    Messages:
    10
    Location:
    North East
    This is a 20 AMP branch circuit that is going to run to a detached garage. The conduit is 3/4, what is the best way to transition from the romex comming from the main panel to the LB.

    Reduce the LB outlet to 1/2" run the conduit up into a jbox (handybox), then connect the romex to the jbox and splice.

    [​IMG]
  2. jwelectric

    jwelectric Electrical Contractor/Instructor

    Messages:
    2,534
    Location:
    North Carolina
    First let’s make sure that we are not installing NM cable in the conduit underground. To transition from the underground conductors to the NM cable can be done in the LB if the LB is marked with Cubit Inches and the volume fill is not exceeded.

    If you desire to have a junction box I would recommend getting a 4X square that has both ½ and ¾ knock outs and the problem is solved.
  3. remster

    remster New Member

    Messages:
    10
    Location:
    North East
    Thanks, the wire in the conduit will be individual THWN.

    Out of curiosity, how hard would it be to pull 12/2 UF through 3/4" about 40feet with (2) 90's.
    Last edited: Jun 17, 2007
  4. jwelectric

    jwelectric Electrical Contractor/Instructor

    Messages:
    2,534
    Location:
    North Carolina
    I have pulled two 12/2 UF cables in 3/4 but it was a pain. You are doing the right thing with THWN
  5. Bob NH

    Bob NH In the Trades

    Messages:
    3,317
    Location:
    New Hampshire
    Because the UF must be treated as a round wire with a diameter equal to the greatest width of the cable, two of them might not meet maximum 31% fill requirement for two conductors in a 3/4" conduit. The maximum allowable width of the UF would be 0.405".

    If you are considering two circuits (based on your two UF question) you would be better off to run a multiwire branch circuit where you can get two full 20 amp circuits with two hots, one neutral, and one ground; just 4 conductors. A multiwire branch circuit qualifies as a single circuit per 250.32(A) Exception. With two or more separate circuits you need a ground rod (probably two ground rods) if you have two circuits.
  6. Alectrician

    Alectrician DIY Senior Member

    Messages:
    689
    1. Use a WP box instead of an LB

    2. Never use UF.
  7. remster

    remster New Member

    Messages:
    10
    Location:
    North East
    What type of waterproof box would have a 3/4 hole in the back?

    [​IMG]

    If using a waterproof box, I will be able to splice the romex to the thwn within the box, should I extend a piece of 1/2 PVC conduit out the top of the box and run the romex down into the box, is this allowed?
  8. Cass

    Cass Plumber

    Messages:
    5,980
    Location:
    Ohio
    I'm curious...why the blanked statement "Never use UF"
  9. remster

    remster New Member

    Messages:
    10
    Location:
    North East
    I would like to do this as neat as possible is this what are you refering to by using a WP box? Then do the splice within the WP box.

    Is it OK to have romex run directly into a piece of PVC conduit and down it, without any kind of conector on the end of the conduit.

    This is an unfishing basement with a stone foundation will never be finished.
    Last edited: Jun 18, 2007
  10. jbfan74

    jbfan74 Electrical Contractor

    Messages:
    131
    Location:
    Newnan, GA
    If I was doing this, from your picture, I would penetrate the wall above ground into a wp box, then run pvc down into the ground. Inside this box, you make the connections from romex to thhn/thwn. Place a sleeve of pvc through the wall into the back of the wp box.
    If you use a metal box, be sure to bond the box to the ground wires.
  11. remster

    remster New Member

    Messages:
    10
    Location:
    North East
    I went with this method because I do not want any visible conduit outside the house, and the foundation already has a easy pathway to get conduit through.

    With that being said, how would you tackle it assuming you have 3/4 PVC entering the basement as pictured. Is it OK to run the romex directly down the conduit into the WP. Also I am not sure what WP would have a 3/4 hole in them, without getting a large one, that was why I was going to go with the LB initially.

    Thanks Guys, I like hearing how different people would do it.
    Last edited: Jun 18, 2007
  12. jwelectric

    jwelectric Electrical Contractor/Instructor

    Messages:
    2,534
    Location:
    North Carolina
    If you penetrate the wall below grade you will have a hard time stopping the wall from leaking when it rains.

    I don’t see the need to spend the money for a weather proof box when a regular 4 square will serve the same purpose.

    Yes it is alright to install a chase pipe down the wall to protect the NM cable. This pipe will need a fitting on the end to prevent damage to the NM cable where it enters the pipe.
  13. remster

    remster New Member

    Messages:
    10
    Location:
    North East
    The foundation is 100 years old so it heavy rains it could get damp, there is a dirt floor in the basement I will not be introducing any more water.

    That is why I wanted to go with a LB entrance, because it is small and it attaches easily to the 3/4, then out of the top of the LB go up with a 1/2 condiut into a jbox near the joists and do the splice in the jbox. The splice would then be in a dry location above ground.

    I think I will go this route.

    [​IMG]
    Last edited: Jun 18, 2007
  14. Bob NH

    Bob NH In the Trades

    Messages:
    3,317
    Location:
    New Hampshire
    I would use an LB and a short piece of conduit to bring the conduit in the basement up above grade level and connect to a metal box using a terminal adapter (a male adapter). Run your THWN to that metal box and connect to the Romex in that box. Be sure you connect the grounds from the Romex and the THWN to the metal box.

    Don't use UF in the house; it is legal but it is a sure sign of an amatuer.

    If you want two circuits in the garage, then use a multiwire branch circuit as I described above to take advantage of the code exception to avoid ground rods at the garage.
  15. remster

    remster New Member

    Messages:
    10
    Location:
    North East
    That's my plan, I am just going to do a single 20AMP circuit for now. Its basically for lighting and a receptacle for occasional use.
  16. Alectrician

    Alectrician DIY Senior Member

    Messages:
    689
    I misread the diagram this morning. I thought you were going to penatrate the wall ABOVE grade. If you DO penetrate above grade you will avoid the potential water leak and you will have a source for future outdoor electrical

    Instead, use a 4square box. You have more room for the splice, you can ground it and you can add to it. Transition to 1/2" emt up the wall. (anything over 18" of PVC looks bad). No real need for the second box up top...just sleeve the romex down the wall.....OR....extend the 3/4 conduit up the wall and put a 4s box up high.

    There is always several ways to run pipe/wire. I don't usualy decide till I get there and have a real look at things.


    PS. I said NEVER use UF because A) it's is vulnerable underground, B) you can't replace it if it faults or add to it, C) it is difficult to work with (strip sheathing)
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