Electrical – What fitting do I need to ground EMT at the residential electrical panel

Your final wire size selection for the ungrounded conductors was exactly right at #2 copper. Your neutrals, however, could have been much smaller. You are allowed to calculate the total unbalanced load and in turn size the neutral accordingly. You still must apply the ambient temperature derating factor and you are required to at least match the size of the grounding conductor. For example, if your total calculated unbalanced load on the neutral was 25 amps and the ambient temperature was negligible, the ampacity table would allow for only a #10 AWG wire to carryn the neutral current, but because the neutral cannot be smaller than the grounding conductor you would still be required to use a #6 AWG. I have the tables underlined in my codebook but don't have it on hand , sorry. The minimum size grounding conductor chart chart is in article 250. Just found this on Mike Holt's website: { The grounded (neutral) service conductor must be sized to carry the maximum unbalanced load in accordance with 220.22 and must not be sized smaller than required by 250.24(B).}

The sub panel will need the ground to be separated from the neutral. The only place they are joined is inside the main breaker panel. This prevents open neutrals between the main and sub panel from sending current over the ground, and possibly electrocuting someone if a better path to ground can be found.

For the 3 way switch, I'm guessing you need to trace more wires, or you have a smart switch of some kind. You'll need to check the switches first, and then start tracing the cables on each end to see where they go. I'm guessing a second line is running just for the 3 way switch that you haven't found.