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I'm wiring my workshop and want to use a common ground wire for multiple circuits. I've found several answered questions here about using a common ground wire but I haven't found one for my specific situation. The wires are running in 1-1/4" PVC conduit under the slab from the breaker panel on one wall to another wall about 50 feet away. I have one 50-amp breaker feeding a 240v outlet and six 20-amp breakers feeding 120v outlets, all with THHN. The 50-amp circuit will use 6 AWG power wires and an 8 AWG ground wire while the 20-amp circuits will use 12 AWG for power, neutral, and ground. I know 12 AWG for a 20-amp circuit may be overkill but I was able to buy a few thousand feet of 12 AWG still on the spools from a local school auction for $100 so I'm going to use it :) All the wires from the conduit go to first a 6x6x4 electrical enclosure and then to the individual outlets. From other questions here, it seems that having a single ground is not a problem but I'm wondering if it's OK to tie that many circuits into the 8 AWG ground wire. I'm planning to use a ground bar to connect the ground wires in the 6x6x4 enclosure. In case the description above isn't clear, I included a diagram of what I have in mind. Please ignore the color of the lines/wires in the drawing; I'll use the correct wire colors for the installation. The conduit fill calculation is good but I've seen some posts that mention other adjustments that need to be made if there are a certain number of current-carrying wires in conduit, e.g. de-rating. Any feedback on all this would be appreciated.enter image description here

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    Where did you get the idea that “12 AWG for a 20-amp circuit may be overkill”? It’s the bare minimum (assuming copper obviously; for aluminum you’d need even bigger - #10).
    – nobody
    Nov 11, 2023 at 2:59
  • All Conduit, or some NM or SE cable? Metal or PVC? Are you familiar with MWBC configuration? Nov 11, 2023 at 4:04
  • Is this a standalone building? Because if it is, you can't run multiple circuits to there of the same type and will need to install a subpanel to get this many circuits.
    – KMJ
    Nov 11, 2023 at 6:39
  • Code reference for what I mentioned is 225.30: up.codes/s/number-of-supplies
    – KMJ
    Nov 11, 2023 at 7:21
  • Please break your multiple questions into multiple questions. You have an answer about sharing the ground already, so leave that one here. You have a humongous problem with derating by running 7 circuits in a single conduit; you can solve that problem with multiple conduits or a sub-panel, or by buying some vastly larger wire for all the circuits. Buying just enough vastly larger wire to feed a sub-panel is usually the smarter path.
    – Ecnerwal
    Nov 11, 2023 at 14:44

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Having multiple circuits share a grounding wire is A-OK

NEC 250.122(C) permits you to have multiple circuits in the same conduit or cable share a single grounding conductor:

(C) Multiple Circuits

A single equipment grounding conductor shall be permitted to be installed for multiple circuits that are installed in the same raceway, cable, trench, or cable tray. It shall be sized from Table 250.122 for the largest overcurrent device protecting circuit conductors in the raceway, cable, trench, or cable tray. Equipment grounding conductors installed in cable trays shall meet the minimum requirements of 392.10(B)(1)(c).

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