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I’m planning on upgrade my main panel. I currently have a Zinsco 100amp panel and am planning to upgrade to a 200amp panel. I’m located in Los Angeles, CA and have already got the spot from the power company. My panel needs to move about 15 feet closer to the front of the house. The existing and future location of the panel is such that they are on an exterior wall on the side of the garage. The back of the panels can be accessed from inside the garage. The garage walls and ceiling are drywalled, but I don’t mind cutting holes and re-patching as needed.

My main dilemma is how to run the circuits from the existing panel to the new panel. There are ten 15 or 20 amp circuits, one 50 amp and one 60 amp circuit. I have gotten multiple opinions on how to relocate them while using the existing Zinsco panel as a junction box and splicing the wires in this box. One opinion is to extend each circuit individually with Romex to the new panel through the ceiling of the garage (it’s closed with drywall, but there is space on top). Sounds like this would mean there would be about 15 Romex wires running. Alternatively, one consideration was to run three 1” EMT conduits along the inside of the garage wall and pulling individual wires through the conduits. Lastly, there was another consideration to connect both boxes with a large EMT conduit such as 2” and running all the wires through this conduit. One concern I had about this last option was that the wires may get too hot in just one conduit.

Any suggestions would be greatly appreciated! I also don’t know if all of these options are up to code or not.

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    One alternative might be to make the old panel a subpanel of the new one, at least as an initial cut-over stopgap. Though I put my new panel where the old one was specifically to avoid having to worry about rerouting existing circuits, and put a smaller secondary at the middle-back of the house for planned new circuits.
    – keshlam
    Dec 25, 2022 at 4:39
  • Can you use a meter-main at the new location then replace the existing panel with a new subpanel in the current location? Dec 25, 2022 at 5:07

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I like @mmnassehkatz comments Here is my two cents worth. I see two approaches:

  1. Install the new panel wherever, run Romex or conduit to the old panel, which you will have gutted and be using it strictly as a junction box...If conduit, paying attention to fill capacity, etc.

  2. There are pretty strict rules on the length from the meter base to the main panel as they are considered "unfused conductors" But if you use a meter / main, it's no longer an unfused conductor allowing you to feed the old panel location. So this idea means you'd install a meter/main with the main feed wires going to the location of the old panel. You'd rip out the old panel, replace it and of course reconnect everything including the main feeds. This way, you may be able to avoid a bunch of splices.

I've helped friends and relatives do it both ways: The advantage of a new location for the new panel is you can wire everything ahead of time and just have the PoCo transfer service after inspection and no pressure. Doing an in-place replacement means no power until you're done, unless you have a generator.

The advantage of an in-place replacement is no new wires to run except from the new meter/main, but again, no power while you're working on it.

Lastly, congrats on replacing the old Zinsco panel, they are junk.

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  • You’ve all been extremely helpful! I’m thinking the method the works best in my situation is option #1. Assuming I use EMT to connect the now junction box to the new panel, would I need to run ground wire(s) between the two boxes? Certainly the new panel will be grounded with stakes and to the water main.
    – Jay
    Dec 25, 2022 at 5:50
  • If you employ a meter / main, technically the main panel becomes a sub panel, meaning you'll have to isolate the ground from the neutrals, IE: don't bond the ground and neutrals in the panel fed by the meter/main. Personally I think it's stupid, but it is what it is and it's a code requirement. ..........Yes, option #1 gives you time to install everything before transferring power to the new panel. If you like my answer, I'm going to make a shameless plug: Please give me an Up-Vote, Moma needs a new pair of shoes! LOL Take Care and DIY on. Dec 25, 2022 at 5:58
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There is no requirement to have "the circuit panel with all your breakers in it" outdoors.

There is a requirement to have the main breaker outdoors, and historically the cheapest way to do that was to use an "All-in-one" panel on the outside of the house. California is covered with these. Since this requirement went in nationally, "Meter-mains" are now popular and affordable. That allows just the meter and main to be outside, with the "panel with all your breakers" to be inside.

And that is valuable because "all-in-one" panels are notorious for having too few breaker spaces for a house. As manassehkatz discusses, the "X spaces Y circuits" number is pretty worthless because most modern breakers can't be double-stuffed.

So an option is to have a meter-main outside then a short conduit connecting to a regular panel on the interior. That panel doesn't need a main breaker but there's no harm if it has one.

Or the location of this panel could be anywhere. Outside where the original panel was, or even inside the wall at that same site.

The only issue is that a panel requires a working space of 30" wide x 36" deep (stand-back distance) that must be kept clear at all times.

Now on interconnecting conduits, there are indeed thermal limits specified in 310.15(B)(7) but it involves a little bit of math. For circuits 15-20A, it's very simple - no more than 4 circuits per conduit of any size. Thus, the "1 fat conduit" idea doesn't work.

For 30-40A circuits, up to 3 circuits in a conduit is fine. Beyond that you have to do the math. The important thing is that for most wires you are derating off the 90C thermal rating of the wire, even though you are usually using the wire at 60C thermal rating.

  • 10 AWG copper is 40A @ 90C.
  • 8 AWG copper and 6 AWG aluminum is 55A @ 90C.
  • 6 AWG copper and 4 AWG aluminum is 75A @ 90C.

Also, here's a time-saver - in 120V/240V split-phase service, ALL circuits count as 2 wires even if they are "2 hots and a neutral". Thus:

  • 2-3 circuits have an 80% derate off the above number.
  • 4 circuits have a 70% derate.
  • 5-10 circuits have a 50% derate.

So for instance 10 AWG copper being one of 4 circuits in a condit, that's a 70% derate off 40A, giving 28A. If the load is actually 28A you're fine. Otherwise you'll need to use larger wire or fewer cables in conduit.

Likewise #12 wire (30A @ 90C) being one of six circuits, gets a 50% derate to 15A. It can only be used for 15A circuits.

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The "wires may get too hot in just one conduit" concern is in fact very real. There are multiple rules involved, but essentially if you run more than a few circuits in one conduit then you have to derate the wires, which results in having to use bigger wires, that cost a lot more than just running additional conduits. There is an exception for 24" or less, but you are way beyond that.

I do wonder a bit about having to move 15' away from the old panel.

My new panel right edge is just inches to the left of the old panel location left edge. In my situation, the move was required due to working space (the laundry sink is ~ 20" from the front of the old panels) but was practical anyway because it allowed doing the work a circuit at a time instead of ripping off the old and putting everything in the new all in one day, which based on the problems we found along the way would not have been a good idea.

But back to your panel. Why did the utility tell you it needs to be 15' away from the current location? If the new meter will be in a meter main then it should not be an issue at all - just run a big circuit from the meter main to your new panel at the old location (and don't use a 42-space meter main). If the new meter will be at the new location and they want the main panel right next to it, it might be cheaper to put a small panel next to the meter and run just a couple of big loads (e.g., 50A and 60A) directly to it plus a big feed to a new panel at the old location. The new panel at the old location would be a subpanel, not a main panel, but you could use a big "main" panel and just remove the neutral-ground bond.

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    Thanks for your reply! The reason I need to move it is that the existing panel is about 16 feet from the front corner of the house. The power company requires that the new panel be 18” from the front corner of the house. I already bought a 24 space 42 circuit Siemens main panel I was planning on using. But your idea of making it into a new main breaker at the new location and a sub panel at the existing location also seems like a good option!
    – Jay
    Dec 25, 2022 at 3:03
  • Keep in mind that a 24-space main panel is closer to a 24-circuit panel, because many circuits require GFCI or AFCI which are not available in half-size breakers. In my case, I didn't need any of those breakers as all the circuits in the new panel were existing circuits from the old panels and everything all in essentially the same space. You may have an issue if the 15' extension makes everything "new". Depends on local rules. If your circuit count is right (~ 10 120V, 2 240v) even at 24 spaces you should be OK. I'd put that in the "old" spot and same or smaller at the meter. Dec 25, 2022 at 3:12
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    But to complicate matters, the panel needs to be semi-flush because a flush mount panel would stick out too far. I’d prefer to not have to cut the stucco for two panels. Do you think running each circuit as a Romex is feasible…and up to code?
    – Jay
    Dec 25, 2022 at 3:12
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    Thank you! I’d be running the Romex in the small crawl space in the garage (can’t actually crawl in there but it’s more than big enough to run wires). As long as that’s considered up to code, that may be the simplest option vs running multiple EMT conduits between the panels and pulling individual wires in the conduits.
    – Jay
    Dec 25, 2022 at 3:36
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    I hardly ever comment on DVs but who and why was this answer DV'd? IMHO it's very fine answer. I think SE should require an explanation from the person DV'ing an answer Dec 25, 2022 at 3:52

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