How do I fix the AC unit to be connected properly to its circuit? How should the AC Unit/Garage/Subpanel be setup? Maybe I can separate the neutral and ground, then ground by connecting to the garage ground wire? If you want to note any other changes to make, you can do so.

Notes: The "Junction Box" is where the current electrical meter is located. A new meter pole was installed in the corner of the property. Thus, the old meter will become the "Junction Box". The "Main Panel" will have a bonded neutral and ground. The "House Main" will have a separated neutral and ground. The "House Main" will be grounded through the SER coming from the "Main Panel". The "Garage" is detached from the house and has an Ufer ground.

Line diagram

  • 1
    Are the house and garage separate structures, or two parts of the same structure? Oct 4, 2016 at 22:24
  • Separate structures.
    – Andy
    Oct 4, 2016 at 22:27

1 Answer 1


Given that you are feeding two separate structures, I see two problems with your setup so far:

  1. The house is relying on the grounding electrodes at the pole, which improperly multiplexes the equipment grounding conductor from the panel to the house with the grounding electrode conductor for the house. This is easily fixed by driving and connecting a ground rod or grounding to an underground metal water pipe at the house, using #4 bare copper or equivalent Bare Armored Ground cable if you prefer.
  2. The neutral and ground need to be separated at the garage subpanel, and a ground wire needs to be run from the main panel . This requires pulling the bonding screw or strap from the panel (it'll be green on more modern ones), installing an extra ground bar to the panel (ground bar kits are available for all panel types in current production, just ask your local electrical supply house; if you can't find one, post here with information/photos of the panel and we can help), and moving the ground wire connections over to the new ground bar, as well as pulling a #8 (or larger) bare or green THHN/THWN through the existing conduit to serve as a new ground wire -- it will connect to the combination ground/neutral bar in the main panel and the new ground bar in the garage panel. (You have plenty of room in the conduit, by the way -- roughly 680mm^2 used to 1660mm^2 available by the 40% fill rule for more than 2 conductors, and the new wire puts you at roughly 710mm^2 used.)

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