I have a Siemens MC30 meter combo panel. I need to separate the meter from the service panel to allow a whole house generator transfer switch between the two. The only way I know to attack this is to

  1. install a new, separate meter
  2. turn off electrical service
  3. replace the service panel
  4. install the transfer switch
  5. pass the inspection
  6. restore service, which may well involve running new underground service cables.

Does anybody have any ideas which avoid moving the service entry location to the meter (and avoiding rerunning connectors to the transformer pad) and minimizing the down time?

  • 3
    Replacing the meter with a solo will involve the power company coming out and removing the service drop. That is the only way to de-energize the meter pan, and working on it energized is not an option. They will not reinstall the service wire until they see permits and inspections done on the new meter pan. Consider a simple generator interlock, which easily retrofit into many panels. May 24, 2021 at 20:26
  • 1
    Is there a reason you want to do whole house transfer instead of moving the standby loads to a subpanel? What loads are you trying to run off the generator? May 24, 2021 at 23:26
  • 1
    I cannot find anything on a Siemens MC30 and I suspect it actually has a different model number. Typically Siemens meter-main-combo panels have complicated model numbers which inside their figures also mention main breaker ampacity and number of breaker spaces. E.G. M2440B1200 would be a believable model number for a 24-space 40-circuit 1-phase 200-amp panel. See where 24, 40, 1, and 200 are all apparent in the model number? May 25, 2021 at 4:05
  • 1
    Can you post photos of the labeling on the inside door of your existing meter-main? May 25, 2021 at 11:44
  • 1
    The load calculation for the whole house - Water heater, heat pumps, appliances, lighting, is about 20KW considering transient effects. Hence the 22KW generator. Utility is Duke Energy - Carolinas
    – AKG
    May 28, 2021 at 12:55

4 Answers 4


Will this be an automatic transfer switch or a manual one? If manual, you might be able to relocate a couple of breakers to make room for a mechanical interlock, there are many available and are code legal. They prevent the main breaker and the generator breaker being turned on at the same time. If a portable generator, you'll need a generator inlet to connect to. If a permanently installed generator, it'd be hardwired to the generator breaker. This assumes it's not a split bus panel, in which case, this wouldn't work AND BE DANGEROUS.

If an ATS... IF and this is a big IF! I couldn't find detailed images of your meter panel combo, but IF (THE BIG IF!) the feed from the meter is wires and not a bus, it might be possible to run conduit to the ATS and rewire it to put it "in front" of the breakers. Technically then the breaker part of the meter/ breaker combo becomes a sub-panel and you'll have to isolate the grounds from the neutrals, which might require some re-wiring.

What you're attempting is a pretty big deal, and my advice is only a suggestion. Probably Harp will weigh in with one of his "novels" and give better advice than me, but this is a starting point.

As much as I hate to say this on a DIY site, you may need to call a pro.

  • @brhans Thanks for the edit. But I have no idea why the dash was appended to the end of each paragraph. That's never happened to me before that I know of and I surely didn't enter them myself. Weird. and yes, I misspelled bus! Thanks May 24, 2021 at 18:10
  • Thank you all for your helpful comments. (a) I was planning on a ATS to spare my wife any decisions or interventions in a power outage when I am not available. Also, this is a 22KW Generac, so I believe I will need a separate meter base anyway. (b) I have attached some image links in the second comment above. The meter - panel connection is shown in this image: <img src="akgreen.com/images/panel4.jpg" width="300" height="400"> Your suggestion is excellent, but I cannot modify the meter base to allow egress for the connectors (per NEC) (c) I've called several pros - not impressed
    – AKG
    May 25, 2021 at 20:12

Generator interlock. That was easy

First, if you just want a manual transfer switch, these can be easily installed as a generator interlock in the vast majority of panels. This is simplicity itself: install a breaker in a particular location in the panel and backfeed it. Install an interlock, a simple see-saw mechanism that assures only one: the generator breaker OR the utility breaker, can be on at once.

Such interlocks typically cost under $100 (as low as $30 in Siemens' case).

Otherwise, install a second meter pan

Use a modern "meter-main". Also install riser, weatherhead and service entrance cabling. Then, call the power company and have them move your service drop over to the new weatherhead.

Here's the problem. The power company won't install this unless they see that you pulled the proper permits from the city and got everything inspected. In turn, the City will want to see what you're doing with your new panel. So now, you're "in it" for installing a whole new service panel, *and having the house 'down' while all this happens. We're into thousands of dollars at this point, much of that in hotel bills!

"Generator subpanel" is the least bad option

assuming you want an ATS. Because the generator subpanel doesn't require the power company to get involved. You can move circuits one at a time, at your leisure, without taking house power down for days (most of which will be sitting around waiting for inspections and the power company).

This also permits a smaller generator, since a generator under an ATS must be sufficiently large for all the loads to be served. With a generator subpanel, you can pick a subset of your loads, so you're not having to install a yellow Cat generator only because of loads you're not even that attached to.

  • Thank you for your comment. Right: I'm going to look at putting in a 100A breaker and generator interlock. Easy Peasy. Second meter pan is sort of what I'm trying to avoid as you observe. I have the permit, though, and can't install this without an inspection and wouldn't anyway. I'll think about a generator subpanel, but I already have the 22KW generator on site.
    – AKG
    May 25, 2021 at 20:27
  • I'm back with an update. After researching leads from this forum, it is pretty clear that separating my Siemens MC panel into a separate meter base and service panel to add the ATS will be a real bear. I have decided to go with a manual transfer switch and mechanical interlock as suggested in comments. I'd like to use a Siemens QN2150 breaker for the generator circuit. <img src="akgreen.com/images/breaker_opts.png" width="300" height="400">. Alternative is Siemens Q2125. Needs to fit <img src="akgreen.com/images/panel5.jpg" width="300" height="400"> Will the QN2150 fit?
    – AKG
    Jun 19, 2021 at 13:14
  • The qn2150 goes in a large main breaker slot. The 125 goes in a branch breaker slot. Jun 20, 2021 at 2:50
  • Monica, thank you for the reply. I was trying to include an image of both and the panel; did not know images cannot be included in comments. I interpret "branch breaker slot" to mean a panel position where one normally installs a 20A breaker, or in this case, a 240V double breaker. My confusion results from a Siemens QN2150 spec sheet which describes it as a "Branch circuit breaker for a Siemens Single Phase Load Center". If correct, then it will have to install in 4 slots, spanning both busses. Can that be correct?
    – AKG
    Jun 21, 2021 at 15:40
  • The spec sheet is here: downloads.siemens.com/download-center/…
    – AKG
    Jun 21, 2021 at 15:40

With help from many of you, I have completed installing a 22K Generac standby generator, powered by propane, and tested it. As noted above in my May 25 post, my service panel is a Siemens meter-combo unit, and the ensuing discussion resulted in the conclusion that my plan to use an ATS wasn't possible without extensive and expensive work to separate the service panel from the meter base. So, I opted to for manual control. This created a number of challenges:

  1. what breaker to use in the service panel to bring the generator online [Harp helped to settle on the QN2150, sourced via Amazon]
  2. Where to find a generator/main interlock overlay for my breakers [after ordering the wrong one twice, I finally found the EPSBPK07 on Amazon and it did the trick
  3. how to "fake" the transfer switch control wiring that keeps the generator's battery charged.

I ended up installing a dedicated 15A circuit in my panel to supply the 120VAC charge the generator would normally be getting from the transfer switch when the generator is off-line. This was an educated guess on my part - nobody from Generac would give me a clue that that was an option. So, its done and it works. All of the above begs the question: why DIY? I asked a local dealer for a quote. For an ATS turnkey system, the price tag was $12000. If I did all the fuel and electrical work myself, the quote was $9000. The generator shipped to me from Grainger was $6000; breakers, connectors, and miscellany maybe $500. Yes, I had to sacrifice the ATS design, but I can live with that. If anyone wants exact details and pictures of the installation, I'll be glad to supply them. As an addendum, requested by ThreePhaseEel, the load calculation for the whole house is 18KW, and I want the generator to carry all of it. I still have future barn and shop loads to think about, hence the choice of the 22KW. I have been living for the last 25 years with a 5500W generator powering "selected" circuits, and I decided enough of that.

  • I broke this up a bit to improve readability, please feel free to edit some more into some paragraphs to help others be able to digest the torrent of words.
    – FreeMan
    Oct 21, 2021 at 22:12
  • What loads in your house do you want to run on standby power? Are there loads in your house you don't want to run on the generator, for that matter? Oct 22, 2021 at 1:44

Hard to say without a lot more info (pictures of the existing installation, how big and how full is the existing panel, how much really needs to be on the transfer switch, etc.) but one option may be:

  • Add a new large panel, selected with generator interlock, etc. in mind, next to the existing panel. Run multiple conduits between the two panels. If they are close enough (24"?) then you have to be concerned with conduit fill but not multiple-circuit derating. One conduit is for the main feed from the existing panel. The others will be for loads moved from the existing panel.
  • Put a double-breaker in the existing panel large enough to handle all expected loads and connect it to the new panel. If the existing panel is full, transfer at least one circuit to the new panel now to make space.
  • Install the generator feed/interlock in the new panel.
  • Transfer other circuits as time permits, up to the full load of the panel (max determined by feed from main panel and by generator capacity). If existing circuits don't have enough wire to reach to the new panel, you can extend them in the existing panel (wire-nut to appropriate color/size wire).

This will allow you to leave some loads (e.g., clothes dryer, electric oven) on the old panel and not have to worry about turning them on during an outage and overloading the generator.

  • Thank you for your comment. I will have to think it through, but perhaps I have added useful information in prior comments, also pictures. But lets say I add a new large panel next to the current one. See panel4 image. <img src="akgreen.com/images/panel4.jpg" width="300" height="400"> I will have to check whether it is OK to extend connectors to a new panel.
    – AKG
    May 25, 2021 at 20:21
  • The biggest factor with adding another panel is usually space. You need space on the wall to put it and you need space in front of the panel for access. May 25, 2021 at 22:28

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