Wires from Main panael to Subpanel in two separate raceways?

Discussion in 'Electrical Forum discussion & Blog' started by electrotuko, Aug 15, 2013.

  1. electrotuko

    electrotuko New Member

    Messages:
    47
    Location:
    Chicago, IL
    I want to ad a 80A subpanel, located right to main panel, not enough room for required 1" metal conduit to run four 4 AWG (L1, L2, N, GND) THHN wires in it.
    Can I run two 3/4" conduits that each would have two wires in them, like L1, L2 in first conduit, N and GND in second conduit?
    Last edited: Aug 15, 2013
  2. Murphy625

    Murphy625 Member

    Messages:
    149
    Location:
    Michigan
    I believe that would create an induction heating circuit... Not sure if it would really make a difference with such a short run and low power circuit but I bet its not allowed.
  3. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,843
    Location:
    Cave Creek, Arizona
    Why don't you have enough room for a 1" conduit, but enough for two 3/4" ones? Does not sound logical.
  4. jwelectric

    jwelectric Electrical Contractor/Instructor

    Messages:
    2,540
    Location:
    North Carolina
    Three #4 THW copper conductors will fit inside any type of metal conduit and there is no need for an equipment grounding conductor as the metal pipe is the EGC as outlined in 250.118
  5. DonL

    DonL Jack of all trades Master of one

    Messages:
    4,333
    Location:
    Houston, TX
    I would install the Ground wire also, even if NEC does not require it.

    You are bound to hit plastic down the road.


    Better safe then sorry.
  6. Speedy Petey

    Speedy Petey Licensed Electrical Contractor

    Messages:
    996
    Location:
    NY State, USA
    This! ......
  7. electrotuko

    electrotuko New Member

    Messages:
    47
    Location:
    Chicago, IL
    Thanks for all your advises.
    Re garding "enough room for a 1" conduit, but enough for two 3/4" ones? Does not sound logical".
    Very simple, subpanel mounted next to main panel, to make a metal conduit from one space between 2x4 studs to another requires either felixible metal conduit or several offset pieces. 1" flex metal is very expensive, sold only in 50' size. I already have 3/4" a piece. If use rigid matal an several offesets - this will not make nice compact, close to wall implemenattion. This what I thought. I could be wring ofcourse.
  8. DonL

    DonL Jack of all trades Master of one

    Messages:
    4,333
    Location:
    Houston, TX
    I would just use the proper type of wire and ditch the conduit, if it is that big of a problem.

    Sounds like you should have upgraded the main panel to do it correctly. Will your Service support the extra load ?

    Maybe I am missing something.

    What will you be feeding this sub panel with ? What is your Main panel ?
    Last edited: Aug 17, 2013
  9. electrotuko

    electrotuko New Member

    Messages:
    47
    Location:
    Chicago, IL
    DonL, your expectations are right. I am planning to upgrade the main panel from 100A to 150A, adding subpanel to increase an ammount of avalable circuit breakers.
    Need extra capacity for additional electrical water boiler, installing cental air, additional circuits to finish up basement.
    I found the supplier to get 1" felixible metal conduit in a small quantity. Will this right, correctly, to strictly follow NEC.
    I called my electrical provider company and got the similar answer as some others reported (they asked their service providers) on the web asking about upgrading service from 100A to higher.
    The inspector over the phone told me that no worry, go ahead and use 150A or even 200A panel, since they assume that my load will never be continuous for such highger rate. Service will support this.

    I am aslo adding an additional GND rod, spaced 11' from original one, 6 gauge solid copper coonects to the meter box. Also will beef up wires from meter box to main panel using 2/0 copper wires.
    Last edited: Aug 17, 2013
  10. jwelectric

    jwelectric Electrical Contractor/Instructor

    Messages:
    2,540
    Location:
    North Carolina
    If you plan on following the NEC then flexible metal conduit would require an EGC to be installed with the feeder conductor and this would require 1 ¼ inch pipe.

    Instead of using pipe it would be much simpler to install SE-R cable which will have two hots, one neutral, and one EGC and is very flexible.

    The assumption that a 150 will be large enough due to you not using things continually is nothing short of silly. The only way to know is to do a calculation.
  11. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,154
    Location:
    New England
    If your load is not going to exceed the breaker, it doesn't really matter what sized panel you choose...just adjust the main breaker size down, if required. Something like a 200A panel may have more slots, and you should be able to find a 150A main breaker for it. Pretty sure this is okay. While you can't put a bigger main breaker in a panel, don't think there's any problem with putting in a smaller one (assuming you can find one that fits!).
  12. electrotuko

    electrotuko New Member

    Messages:
    47
    Location:
    Chicago, IL
    jwelectric, thanks for your comments. Can you clarify why adding EGC would require 1 ¼ inch FMC (in my case I am seeking FMC for mounting simplicuty aand compactness).
    My all four wires are the 4 AWG size. I thought EGC is one of them, the green one. Looking in to Conduit Fill Tables, based on 2011 edition of the NEC, I see that for 1" FMC (or any sort of metal conduit) it specifies four 4 AWG THHN wires. Should not it fit and be OK by NEC?

    jadnashua, thanks for pointing this out. I want to make sure the panle ratging by it self is 150A or more. The busses inside have to be rated accordingly. I thought that I can not use a panle rated for 100A an d install bigger breaker. the second thing - the main circtuit breaker mounting, 150A device does not fit mounting wise in to 100A panel, different connections, cutout positions on the front cover.
    The main power line over the air, from the last pole is 4 AWG wires. Electrical conpany says it is OK for 150A.
  13. cwhyu2

    cwhyu2 Consultant

    Messages:
    1,348
    Location:
    Cincinnati OH
    If you are going through all that trouble to ad a sub panel for more circuits, why don`t you just upgrade your main panel.
  14. electrotuko

    electrotuko New Member

    Messages:
    47
    Location:
    Chicago, IL
    Very simple, tha panel is in the basement, on the wall, where right below the panel (9" space) is a concrete wall down to the floor. It is not enough space, vertically between the concrete wall and bottom of a panel, to convinienly install 30 or 40 space main panel. It is 36"+ high, just too long/tall. The 150A or 200A main panel with 20 spaces, 30" tall metal case/frame fits perfectly. And just next to I will fit 12 space subpanel.
  15. Wet_Boots

    Wet_Boots Sprinkler Guy

    Messages:
    798
    Location:
    Metro NYC
    the conduit fill calculator I've been using flunks 4 #4 THHN wires in one-inch FMC, but just barely, to the point that a bare #4 ground wire used instead of THHN would put you to the good by more than four percent of total fill
  16. electrotuko

    electrotuko New Member

    Messages:
    47
    Location:
    Chicago, IL
    Wet_Boots, thanks, now I got it. Will use bare copper. Always need to think out of box, I keep forgetting.......
  17. electrotuko

    electrotuko New Member

    Messages:
    47
    Location:
    Chicago, IL
    One thing still worries my is that my calculated long term load is approx. 150A, not including short time loads for 1-5 min., such microwave, weel pump, toaster, garage door opener and etc.. The wires through the air are 4 AWG (only between last pole and top of meter riser pipe), riser pipe 1 1/2 inch, wires in it 1 gauge. Everything points out to 150A service capabalities. If I would turn everytning ON simlutaneosly in my house, the load will go up to 200A. I just may relay on the wires being in the air having good ventilation and will not get extrimely hot. I hink this is what power utility guy meant saying no worry you will be fine up to 200A main service panel and 200A braeker in it.
  18. DonL

    DonL Jack of all trades Master of one

    Messages:
    4,333
    Location:
    Houston, TX

    The Length of the wire will determine Voltage drop, and that is what is important.
  19. electrotuko

    electrotuko New Member

    Messages:
    47
    Location:
    Chicago, IL
    is the volatge drop on theat smallest wire distance (pole to meter) is most improtant, or the wwhole voltage drop on all transmition line and only final voltage as lowest line at the meter is most improtant?
  20. Speedy Petey

    Speedy Petey Licensed Electrical Contractor

    Messages:
    996
    Location:
    NY State, USA
    WHY in the world would you use a #4 ground for a 100A feeder???
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