Okay, I have a main panel that is a 1978 2-wire system with combined neutral/ground bar and a 100amp main disconnect breaker. I'm Replacing it with new 200-amp service and all load wiring has been updated and includes ground wiring. The easiest transformation is to add a room and convert the exterior wall where the old panel is to an interior wall and simply put the new panel facing the new room to meet code and avoid a j-box. The old panel is also in a kitchen cabinet. The meter box is on the exterior opposite the original panel box but is being relocated to a new ext. location.

I installed a temporary power pole main disconnect with 2-2-2-4 SER to run 25' in schedule 40 from the disconnect to the old panel until the room is built. To convert it to a subpanel, do I remove one of the existing ground/neutral bars and replace it with an insulated neutral bar and put all load neutrals on the insulated bar plus the #2 neutral wire from the disconnect and all grounds to the ground bar? I'm assuming the 2-2-2-4 SER Al is rated to enter the house to the panel.

Other than the #4 ground wire from the new disconnect to the old panel, does the subpanel also need a #6 bare copper ground from the ground bar to a copper ground rod? I already have 2 ground rods at the main disconnect on the temp pole.

Lastly, there is already a 4-wire subpanel that I had previously wired from the original panel to a workshop and put a ground to a copper rod at that subpanel. If I have my wiring description above correct, is any of this going to affect the wiring arrangement at the existing subpanel of the workshop?

Thanks for any advice/recommendations.

  • What make and model is the existing panel? In many cases, the neutral bar is part of the panelboard interior assembly and can't be "removed and replaced" the way you describe.... – ThreePhaseEel Jan 21 '20 at 0:33

I believe you are very close to being in good shape. Yes, to do it properly, the existing 100 amp panel must have the neutral "floated" (insulated) and not bonded to the ground. All neutrals must go to the neutral busbar and all grounds must be connected to the grounding busbar. Since you have 4 wire from the temporary service, you no longer need the ground rods for the 100 amp service. In fact, I think it's probably not even allowed anymore. Your connection assumptions are correct. Will you be gutting the old panel and basically turn it into a big j-box? That's what I've done in the past and inspectors are fine with it. Being in a cabinet may force the issue going forward.

Regarding the other sub-panel in your workshop, if you have 4 wire feed to it, it's the same drill as your other soon-to-be subpanel...float the neutral and use separate wires for neutral and ground. You shouldn't need a local grounding rod there either anymore. I understand the code, and the rationale for not sharing neutral and grounding in a sub-panel, but not why you can't have local grounding. Maybe someone with more knowledge than me can answer that.

  • If it's a separate building, the OP still needs a grounding electrode system there.... – ThreePhaseEel Jan 21 '20 at 0:34
  • "Will you be gutting the old panel and basically turn it into a big j-box?" I'm building a garage and the new meter box, riser and weatherhead will end up there, with new wiring buried in sch. 80 and returning to the new room 200 amp panel. I will simply gut the original panel box and remove it completely. The new panel will take its place facing into the new room instead of the cabinet and the wiring will be long enough without having to use a j-box. – Mark Ferris Jan 21 '20 at 0:41
  • Will you be gutting the old panel and basically turn it into a big j-box? I plan to gut it and replace it with the new 200amp panel facing into the new room. The wiring will be plenty long enough that I won't need a j-box at all. That should satisfy the code of getting the panel out of the kitchen cabinet and having the required free space in the new room surrounding the new panel with all new breakers. The new panel naturally has the isolated neutral and separate ground, with a new 200amp main breaker. Thanks for the help from everyone. – Mark Ferris Jan 21 '20 at 0:53
  • OK, I get it now. The new panel is replacing the existing one in the same place, but opening on the other side of the wall. Great solution. When you get your new panel, I strongly suggest the "plug on neutral" (PON) panels. With those, you don't need all the pig tails for GFCI & AFCI breakers because there are neutral bus bars that clip on the breaker, just like the hots. ... makes for a much neater panel. Check with your local code/inspectors to see what will need to be GFCI & esp. AFCI protected in your remodel/addition. The rules are complicated. – George Anderson Jan 21 '20 at 2:19
  • Question for ThreePhaseEel: In my neck of the woods (Washington State), they really want outbuildings serviced by 4-wire without a local grounding system. At least I think that. I know that sub-panels in the same building must be 4 wire. I'm going to call the inspector to clarify. I've never seen the logic in not allowing local grounding for sub-panels as long as the neutral is floated. I might be wrong, I'll let you know. – George Anderson Jan 21 '20 at 2:27

Your plan sounds right. Separating the grounds. And 4-wire from main to any subpanel. Using aluminum wire for service and feeder is also wise.

You actually need two ground rods at each building. Unless the one passes the magic test for 25 ohms. But you can't test it, and the cost of hiring it done is more than a second rod. End of the day ground rods are for protecting you and yours, so they're cheap insurance.

You still need the ground wire; that's for returning human-generated current, which is much lower voltage than lightning and ESD, but far too high current for dirt to carry.

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