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Thread: Wires from Main panael to Subpanel in two separate raceways?

  1. #1
    DIY Member electrotuko's Avatar
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    Default Wires from Main panael to Subpanel in two separate raceways?

    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 by electrotuko; 08-15-2013 at 04:15 PM.

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    DIY Senior Member Murphy625's Avatar
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    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. #3
    Moderator & Master Plumber hj's Avatar
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    Why don't you have enough room for a 1" conduit, but enough for two 3/4" ones? Does not sound logical.
    Licensed residential and commercial plumber

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    Electrical Contractor/Instructor jwelectric's Avatar
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    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

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    Jack of all trades DonL's Avatar
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    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.
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    Licensed Electrical Contractor Speedy Petey's Avatar
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    Quote Originally Posted by hj View Post
    Why don't you have enough room for a 1" conduit, but enough for two 3/4" ones? Does not sound logical.
    This! ......

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    DIY Member electrotuko's Avatar
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    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. #8
    Jack of all trades DonL's Avatar
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    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 by DonL; 08-17-2013 at 10:45 AM.
    Theory only works perfect in a vacuum.

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    DIY Member electrotuko's Avatar
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    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 by electrotuko; 08-17-2013 at 11:26 AM.

  10. #10
    Electrical Contractor/Instructor jwelectric's Avatar
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    Quote Originally Posted by electrotuko View Post
    to strictly follow NEC
    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 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. #11
    Retired Defense Industry Engineer jadnashua's Avatar
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    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!).
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    DIY Member electrotuko's Avatar
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    jwelectric, thanks for your comments. Can you clarify why adding EGC would require 1 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. #13
    Consultant cwhyu2's Avatar
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    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. #14
    DIY Member electrotuko's Avatar
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    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. #15
    Sprinkler Guy Wet_Boots's Avatar
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    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

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