Conduit Question

Discussion in 'Electrical Forum discussion & Blog' started by Verdeboy, Sep 21, 2007.

  1. Verdeboy

    Verdeboy In the Trades

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    For minor residential jobs where you need to run some cable outside, is it customary to use EMT, IMC or Rigid? I want to buy a manual bender and conduit cutter, and if I'm only going to use EMT, It'll make the decision easier.
    Last edited: Sep 21, 2007
  2. Speedy Petey

    Speedy Petey Licensed Electrical Contractor

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    Define this. Do you mean conduit runs, or just short sleeves for protecting cable?

    For outside runs I use PVC. In fact for most residential conduit work I use PVC.
  3. hj

    hj Moderator & Master Plumber Staff Member

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    Pvc

    Here, if it is going to be above ground it must be schedule 80 PVC conduit.
  4. jwelectric

    jwelectric Electrical Contractor/Instructor

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    By the term “cable†I hope you are not talking about NM (romex) going in the raceway installed outside.


    What do you mean by “cutter�
    A tubing cutter is very bad when cutting EMT as it leaves a sharp ring on the inside of the pipe and also reduces the size of the pipe as it indents the conduit.
  5. Verdeboy

    Verdeboy In the Trades

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    Schedule 80 PVC it will be. I'm finishing up a minor outdor run (above ground) where someone had used metal conduit. Since I was told he was a "real" electrician, I thought the metal was code. Obviously not.

    BTW, If only PVC is used outdoors, why is metal conduit used in all the carports and up the sides of buildings in the apartment complexes I worked in?

    Also, is there a simple way of bending the PVC? Like using a heat gun or sticking the end in my Jeep's tailpipe? Or do I need to buy a PVC bender?

    As for the conduit cutter, JW, I was looking at the Greenlee, which is advertised as Burr-free and no sharp edges. They also say, you can cut it with the cable inside. Are they lying?

    Attached Files:

    Last edited: Sep 22, 2007
  6. Bob NH

    Bob NH In the Trades

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    You can buy 90 and 45 elbows for PVC, or you can bend it with equipment, or you can use a heat gun if you have patience. I have bent up to 1" Schedule 40 with a heat gun. I have never had occasion to bend Schedule 80.

    If you are careful you can get as good a bend with a heat gun as you will buy in the electrical supply. It is easiest if you can work the piece on a flat surface.

    It is also a violation of the code to bend it with equipment that is not designed for the purpose.
  7. jwelectric

    jwelectric Electrical Contractor/Instructor

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    Eric

    When installing a raceway outside it is a matter of choice as to what is used. EMT, RMC or RNC either would be proper to install outside except EMT will not last long if in contact with earth.

    There is no code requirement that all outside conduits be rigid nonmetallic conduit (RNC) or PVC as some would call it.

    I will not allow the tubing cutter to be used on my jobs. This cutter will indent the pipe and leave a very sharp ring on the inside of the pipe that will damage the conductors as they are being pulled through the pipe. No matter how hard you try to remove this ring on EMT it is all but impossible to remove so no damage will occur.

    As to cutting the pipe with the conductors installed, it would be a violation of the NEC and IRC.
    Again I do hope that with your repeated use of the word “cable†you are not planning on installing NM cable in this raceway on the outside.
  8. Verdeboy

    Verdeboy In the Trades

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    What is the approved cable for this? I've got UF-B and tray cable, but I can buy something else if needed.

    The run is about 20 ft total, starting from an outlet box on an exterior wall of the shop, along the bottom of a stone wall, through the stone wall (~16" wide), up a post of the porch, and terminating in a junction box, which feeds various light switches for the porch, one other outlet, and an indoor/outdoor ceiling fan.
    Last edited: Sep 22, 2007
  9. Bob NH

    Bob NH In the Trades

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    One of the places that tray cable may be installed is in a raceway, such as a conduit. Ampacity is determined per 310.15. You should be able to use the usual ampacities for up to 3 current carrying conductors in a conduit. If you have more than 3 conductors you may be able to use those numbers if the cable has a 75 or 90 C temperature rating and you do some calculations per 310.15(B).

    Underground is considered a wet location so the cable must be rated for that if used in an underground conduit.

    You would need to run the raceway for the full length of the run if you use TC.

    Most people use THHN/THWN in conduit. You can usually pick up a 500 ft roll of #12 on the auction site for about $50 with shipping; #14 a little less. You need a roll of white or grey for the neutral, green for the ground, and any other color for the ungrounded (hot) conductors. You can use the same color for all of the hot conductors if you keep track of wires.
  10. Speedy Petey

    Speedy Petey Licensed Electrical Contractor

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    Actually Mike this cutter will not do as you say. Although I have not used one personally yet it does seem to live up to it's reputation.
    It is made specifically for EMT. It is NO ordinary tubing cutter.
  11. jwelectric

    jwelectric Electrical Contractor/Instructor

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    Sorry bout dat, havn't heard of one yet.
  12. Verdeboy

    Verdeboy In the Trades

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  13. jwelectric

    jwelectric Electrical Contractor/Instructor

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    Didn’t say that you couldn’t install NM cable in conduit but I did say you couldn’t install NM cable in this pipe,
    Even though the cable would be in a raceway the raceway would be in a wet location.
  14. Verdeboy

    Verdeboy In the Trades

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    Okay, I got it.

    But can you explain why individual conductors (inside conduit) like THHN-THWN are safer in locations exposed to weather than Romex (inside conduit)?

    I actually thought the reason why Romex wasn't used in conduit had more to do with difficulty pulling it through (90 degree bends, etc.) especially with the sheathing still attached.
    Last edited: Sep 22, 2007
  15. Speedy Petey

    Speedy Petey Licensed Electrical Contractor

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    Hey, no problem. It's new from Greenlee. I haven't even seen one yet, but I have heard a bunch of feedback.
  16. Bob NH

    Bob NH In the Trades

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    You are not prohibited from using NM in conduit; you ARE prohibited from using it in a wet LOCATION.

    Romex (Nonmetallic, NM cable) often has paper wrapping inside and is not required to be resistant to water. Therefore, you can't use NM cable in any wet location.

    An underground location is considered wet, even if in "waterproof" conduit.
  17. jwelectric

    jwelectric Electrical Contractor/Instructor

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    310.8(C) Wet Locations. Insulated conductors and cables used in wet locations shall be
    (1) Moisture-impervious metal-sheathed;
    (2) Types MTW, RHW, RHW-2, TW, THW, THW-2, THHW, THHW-2, THWN, THWN-2, XHHW, XHHW-2, ZW; or
    (3) Of a type listed for use in wet locations.


    The conductors in NM cable are only required to be rated at 90 degrees and no marking is required on the conductors theirself therefore they can not be installed in a Wet Location.
  18. jbfan74

    jbfan74 Electrical Contractor

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    Newnan, GA

    I have one and use it of the time. It was a little hard to get used to it, to know how far to cut.
    You score the cut, then snap the pipe. It does not work well on short pipe, because you don't have much to hold when snapping.
  19. Verdeboy

    Verdeboy In the Trades

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    Flexible Metal Conduit Questions

    1. Can you use this outside (above ground) or do you need the kind with PVC coating for outdoor use?

    2. What's the best way to cut it?

    3. Do they make outdoor boxes specifically designed to connect flex conduit?
  20. jwelectric

    jwelectric Electrical Contractor/Instructor

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    348.12 Uses Not Permitted.
    FMC shall not be used in the following:
    (1) In wet locations unless the conductors are approved for the specific conditions and the installation is such that liquid is not likely to enter raceways or enclosures to which the conduit is connected
    (2) In hoistways, other than as permitted in 620.21(A)(1)
    (3) In storage battery rooms
    (4) In any hazardous (classified) location other than as permitted in 501.10(B) and 504.20
    (5) Where exposed to materials having a deteriorating effect on the installed conductors, such as oil or gasoline
    (6) Underground or embedded in poured concrete or aggregate
    (7) Where subject to physical damage
    348.20 Size.
    (A) Minimum. FMC less than metric designator 16 (trade size ½) shall not be used unless permitted in 348.20(A)(1) through (A)(5) for metric designator 12 (trade size ).
    (1) For enclosing the leads of motors as permitted in 430.245(B)
    (2) In lengths not in excess of 1.8 m (6 ft) for any of the following uses:
    a. For utilization equipment
    b. As part of a listed assembly
    c. For tap connections to luminaires (lighting fixtures) as permitted in 410.67(C)
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