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  • subpanel questions

    I have been thinking about putting a subpanel in my garage, and I was wondering if I could buy a 100 amp panel, but use a 60 amp QO breaker to feed it. I planned on using a 12 spot square d load center, feeding it with 2-2-2-4. I had looked in the NEC, but can't seem to find it. Just wondered if it was legal. Before you guys tell me to hire an licensed electrician, don't worry. I apprentice for one, just wanted a game plan before I bring it to his attention.

    thanks

  • #2
    Re: subpanel questions

    Yes, that is fine. The "100A" panel is just the maximum.

    Comment


    • #3
      Re: subpanel questions

      thanks for the help

      Comment


      • #4
        Re: subpanel questions

        Yeah!! thats perfectly ok. YOu're using 100A panel and this is completely ok.

        Comment


        • #5
          Re: subpanel questions

          If it's a detached garage be advised of the following;

          225.32 Location. The disconnecting means shall be installed either inside or outside of the building or structure served or where the conductors pass through the building or
          structure. The disconnecting means shall be at a readily accessible location nearest the point of entrance of the conductors. For the purposes of this section, the requirements
          in 230.6 shall be utilized.

          225.36 Suitable for Service Equipment. The disconnecting means specified in 225.31 shall be suitable for use as service equipment.
          Exception: For garages and outbuildings on residential property, a snap switch or a set of 3-way or 4-way snap

          Remember to NOT use the bonding screw that comes inst in the panel, grounds must be isolated, and (depending on city) at least one ground rod driven.

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          • #6
            Re: subpanel questions

            John, can you explain why the ground must be isolated on a sub panel? I've always wondered what the reasoning is for it.

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            • #7
              Re: subpanel questions

              Originally posted by Alphacowboy View Post
              John, can you explain why the ground must be isolated on a sub panel? I've always wondered what the reasoning is for it.
              Objectionable Current

              Comment


              • #8
                Re: subpanel questions

                Originally posted by Alphacowboy View Post
                John, can you explain why the ground must be isolated on a sub panel? I've always wondered what the reasoning is for it.
                During normal use the current is carried on the neutral. The equipment grounds are designed to only carry fault current, eg..shorts to ground. If they are tied together downstream the currents are carried on both the neutral and the ground which in turn is connected to exposed things like plate covers, conduit, thus a presence of voltage on appliance casings.
                The Neutral and equipment grounds are tied (bonded)together at the service panel. If they are also tied together downstream, (causing a loop) it causes parallel current paths that causes objectionable currents. They can overheat wires and surrounding metal by something called hysterisis. Basically, Wiring is usually always grouped in pairs (hot,neut) so the magnetic fields are minimized by wires with current flowing in opposite direction.

                Comment


                • #9
                  Re: subpanel questions

                  Originally posted by Highlife View Post
                  I have been thinking about putting a subpanel in my garage, and I was wondering if I could buy a 100 amp panel, but use a 60 amp QO breaker to feed it. I planned on using a 12 spot square d load center, feeding it with 2-2-2-4. I had looked in the NEC, but can't seem to find it. Just wondered if it was legal. Before you guys tell me to hire an licensed electrician, don't worry. I apprentice for one, just wanted a game plan before I bring it to his attention.

                  thanks
                  If the 2-2-2-4 is aluminum the max breaker size would be 90A, since it does not meet the criteria allowing you to use #2 AL for 100A, other then a bit more trouble finding a 90A breaker, it should cause no problems. People do use #2 AL all the time w/ a 100A for a subfeed but it still ain't right.

                  i

                  Comment


                  • #10
                    Re: subpanel questions

                    Might've messed up on my wire size, re planned it and since I only want 60 amps, I plan on using #4 copper.

                    My biggest concern was the main breaker feeding the panel, my journeyman would've corrected my wire size mistake. Thank god for good teachers

                    Comment


                    • #11
                      Re: subpanel questions

                      my sugestions is to stay with the larger wire size, even if you use (AL wire) as you may want more power down the road, and if you put in the lighter and some one swaps out the breaker for a larger in time the wire will be under sized.
                      Push sticks/blocks Save Fingers
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                      • #12
                        Re: subpanel questions

                        When adding a large load to an existing panel a load calculation should always be preformed to determine if the capacity is available at the service.

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