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I am upgrading from 100 amp service to 200 amp at my house. Our county allows homeowners to do this project. I have enough space to build the new service next to the old service and have the power company do the meter move all in one visit instead of trying to order a "work along" (pull the meter in the morning and hopefully put it back in the evening).

I have a lot of old cloth-sheathed cable and I really don't want to touch it. Instead of moving each individual wire from my old panel to the new, someone suggested running a few 2 inch conduits between the old box and the new box, pulling out the guts of the old box and using it as a junction box.

Any issues or downsides with doing that?

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  • I just went through this (except I hired my electrician rather than do it myself). Thought we'd have several old circuits not reach the new panel but in the end only one needed an extension. One 4" box next to the new panel is a lot nicer than having to leave in one of the old panels as a big junction box (which we initially thought might be necessary). Based on the experience, I'll caution you that the last few steps may take more time than you expect, particularly if you are reusing the old service entrance cable hole in the wall for new cable because then you can't do that part before the Sep 1, 2022 at 4:59
  • meter pull. Pepco (probably most utilities) will let you put the meter back in, and then you call them back to finish up but you aren't left without power. Sep 1, 2022 at 5:01
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    How about make the old 100 amp panel into a sub-panel? (Assuming you don't have a reason to trash the old panel). You can leave old circuits you don't want to touch in the old panel. The main thing is that you have to separate grounds from neutrals in the sub.
    – DoxyLover
    Sep 1, 2022 at 5:20
  • There is water coming in through the old service entrance cable, so I am getting rid of everything from the old weather head to the inside. I should probably remove the guts of the old panel since they have likely gotten wet. The newest NEC (not adopted, but good to look at) requires an outdoor service disconnect, so every panel is now a subpanel.
    – yakatz
    Sep 1, 2022 at 11:52

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First and foremost, ANY time you put a panel next to another panel, you should always connect a number of (at least 3) pass-thru conduits between the two panels.

As convenience pass-thru's for just such applications.

They should be metal and either EMT or RMC. The reason is metal handles your grounding for you. (it also doesn't emit poison gas in a fire). So you won't need to tie the panel grounds together.

It doesn't matter if the conduits are less than 2 feet long, but if more than 2' long, then only 4 circuits are allowed per conduit. That, plus ease of installation, is why I'd rather have several small conduits rather than one huge one.

Second, as long as there isn't anything wrong * with your original panel, you don't really need to remove all the circuits and demolish it. You can simply wire it as a subpanel of the new panel. Again, those convenience pass-thru's make easy work of this, though you would need one 1" conduit to pass through #3 copper for 100A (or if you want to save about $20, 1-1/4" conduit to pass through #1 aluminum wire, which is fine.)

Even if there is something wrong* with your old panel, you can simply use the box as a giant splice box for wires. In that case, for each circuit you must pass through hot and neutral using THHN wire through one of the pass-throughs. And you must take measures to positively identify (for all future maintainers) which neutral is with which hot(s) - colored electrical tape or heat shrink will suffice, or simply use heat shrink to bundle them.

Note that with THHN individual wires, a white #14 to #6 wire can only ever be neutral, and using black, blue or other color tape on it is not allowed to make it a hot. Thus, e.g. blue and green bands of tape on a white could simply mark it as a mate to the black with blue and green.

The only thing is, you can't leave the old panel with gaping open holes in it. Those would need to be blanked over either by 30 of the approved blank cover plates, which are flimsy, or by metal plates of >= thickness riveted on, provided the latter meets the approval of the inspector (no reason why not, as long as it's competently done). Or you could leave all the breakers in to fill the holes, but at that point why not just use them for breakers and avoid disturbing all that stuff?

* Unless they are Zinsco or Federal Pacific, which are not safe and cannot be made safe. Challenger can be made safe by replacing the faulty Challenger Type C/A breakers with Eaton Type BR/C/A. Pushmatic is a fine panel.

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  • Old panel is Square D, but might have gotten wet.
    – yakatz
    Sep 1, 2022 at 12:08
  • @yakatz The breakers themselves are not inspectable internally, and are suspect and must be junked. However for the empty panel, any damage will be completely obvious. If it looks OK, it's OK. Once it's de-energized, if you really wanted to be fastidious, you can even pull out the entire bus assembly (the whole thing) and clean it up with soap and water and an old toothbrush. Rinse it thoroughly is all. Don't try to disassemble the bus assembly unless you're sure you can get it back together. Sep 1, 2022 at 18:15

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