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Community and Q&A

Service Feeders for All-Electric House

andrew84092 | Posted in Mechanicals on

Planning a 400A two-pack pedestal meter/main combo to feed two all-electric houses (1 now, 1 in the future). Tried 3 electricians, none returned my call, so decided to DIY.
Attached is my schematic.  Conduit is so pricey right now that I am contemplating using direct-bury, jacketed MC cable for current house (3” conduit for future house). Voltage drop for aluminum 250MCM, 240v, 200A, 224f one-way run is an acceptable 3.69%.
Any thoughts or suggestions? Thank you

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  1. walta100 | | #1

    Will you want separate meters/ power bills for the two houses?

    Will you start construction on both houses in the next 12 months?

    With my utility if the meter is on the house the home owner buries the empty conduit from the transformer to the meter and the provides the wire as needed for no cost.

    Most locations require any solar to connect within a few feet of the meter so the fire department can shut all the power down from one point. Be sure you understand your local requirements.

    Why would the solar have a sub panel?

    Understand direct burry cables have a much higher failure rate than conduit cables.

    I think the second house should have its own meter and service sooner or later the two houses are very likely to have different owners and be unsaleable. Even if that never happens people will end up arguing about why the bill is so high and thinking the other people are running up the bill.

    Seems to me there is at least some chance the second house will never get built any thing you spend now could be wasted money.


  2. andrew84092 | | #2

    Thanks Walta. Some good points here.
    Utility do not pay for any part of the connection. I even pay for the transformer upgrade. Would cost more to have the utility bring the supply to electric meters on the houses (stricter trench specs., etc.). It was their idea to do a pedestal meter and it makes sense for the site.
    The second house will use the second meter slot on the 400A panel. (Until the second house gets built this meter slot could be used to separately meter the ADU). No timetable for when second house gets built. Want to plan for it, but not over-plan.
    Want to put a separate 100A sub-panel close to where the solar inverter will be and also to run lights and outlets for the main house (don’t want lots of romex cables breaching the garage-house barrier).
    Good thought on the solar disconnect, I will need to check into that.
    I am hoping that direct bury armored MC cable will be as reliable as conduit. It comes in its own aluminum conduit after all. It’s also approved for direct encasement in concrete and indoors.

  3. Expert Member
    Akos | | #3

    Up north it is common to run a big O-pipe (corrugated drainage pipe) and run any services through that. The O-pipe doesn't count as conduit so you still have to use cable rated for direct burial (ie USEB cable) but now it is protected and make replacing or upgrading it a breeze if ever needed. Same for water/phone/cable service.

    If you are in net metered land, a standard 200A panel allows for only 7.6kW of solar because of busbar current limits. It doesn't matter that the solar is on a 100A subpanel, the limit is at the main panel. If you want more solar, I would get one of the solar ready panels which has a dedicated connection for PV.

    I would also check with your local code 250mcm aluminum seems small for such a long run.

  4. Expert Member
    BILL WICHERS | | #4

    I can see a few issues here. The first is that your grounding electrode conductor (GEC) to those plates at the service needs to be sized based on the total cross sectional area of the conductors serving the pedestal. For a 400A service, that is likely to be 450+ kcmil, which means you need #2 copper ground wire here (and I'd recommend either solid or 7 strand wire here, not 19 strand). If you're over 500kcmil or equivalent area, then you need a 1/0 GEC. I would require the wire be connected to those plates by exothermic weld (cadweld or equivalent), and not any mechanical clamp. The same would go for any underground splices in the GEC. The reason for that is that cadweld is forever, mechanical connections tend to loosen and corrode over time. If this were my installation, I would put in several copper clad rods instead of plates, and cadweld them all in a row. Code allows for 20 feet of copper wire buried 30" or more as your ground too, although I'd add at least two 5/8" copper clad rods to the wire (8 foot rods need 16 foot spacing).

    It's good to have additional ground rods at seperate structures if they are far away from the main ground. Your ufer ground takes care of that, and your #4 copper wire is OK here. I would recommend solid wire here. BTW, the reason for the solid or low-strand count wire for grounds is because it has less total surface area per unit conductor cross sectional area, which means it holds up better over time in corrosive enviornments.

    3.69% volt drop is not acceptable. You need to be under 3% on feeders, which would include your meter-to-house run here. You are allowed up to 5% for the entire path from the source to the most distant outlet or appliance. You need to up your wire size.

    I strongly recommend conduit and XHHW conductors here. PVC conduit is spendy, but HDPE duct is not as expensive. Run UL listed (required for power use) HDPE conduit here instead, ideally schedule 80. This material will come on a roll, so it won't need any splices along the route. I would use black with a red tracer here, but you have some options just DO NOT USE YELLOW -- yellow is reserved for gas and oil lines.

    I would not recommend MC cable here, regardless of it being rated for underground use or not. Any nicks in the jacket and that aluminum arbor will rapidly rot away in most soil chemistries. I wouldn't expect you to see any cost savings over wires in conduit, either. It will surely be a whole lot more difficult to install!!!

    LBs have only two connections. An LB has one end and the back as the fittings. What you need here is a large junction box, which would need to be elevated above ground, not buried. You can get small cable vaults too, which are usually made of precast concrete, which is probably a better option here. Hubbell (Quazite) is one manufacturer, but there are many others. This type of box can be installed in the ground with the cover flush with grade, and you can make your electrical connections inside, or just pass through and use it as a pull box (which is a better option here, although you can splice into the ground to at least save a little money with that conductor -- you don't need to run seperate ground conductors for each service, you can use one conductor sized for the larger of the two services and just splice into that).

    I recommend HDPE pipe for the data runs too, to save a little money. You can get it with internal ribs that is a little easier to pull through too (reduced friction with the cables), but that usually costs more and isn't very common. Black PE water pipe rated for potable water use is probably cheaper than PEX for water lines.

    Walter is correct that there are some code requirements regarding disconnection of solar systems. I don't work with those much, so I'm not as familiar with those requirements and won't comment on them aside from mentioning that they are something you need to consider. Note also that excess solar production over the load on the first house would be seen by the meters as billable power for the second house, so you can't "share" that system as you might have been expecting.


  5. andrew84092 | | #5

    Akos/Zephyr7: All very helpful. I am so happy that I have not already purchased that MC cable.

    The Utility Company are going to use 350MCM feeders to the main panel. I don’t think this size is even rated for 400A (I guess they are not bound by the NEC).

    Whether it’s 350 or 400MCM I think you are correct, I need #2 copper wire for GEC at the 400A pedestal. Also appreciate the other practical points on grounding.

    I will make the switch to conduit/XHHW. If I add the JB/pull-box maybe I can use 2” HDPE (count=2) subject to conduit fill requirements. Don’t think I can use a single 3” conduit as this would make the future house pull too difficult?

    I think that I should upgrade the 200A feeder wires from 250MCM, although my main disconnect has max 300MCM lugs. If I went up to 350MCM (2.97% VD) then maybe I could splice on a reducer at the terminations? I believe that I can downsize the neutral 2 sizes (4/0 neutral for 300MCM)?

    And big O-pipe to run water and internet through, genius!

    I obviously need to give more thought to the solar tie in and disconnect.

    Many thanks,

  6. Expert Member
    BILL WICHERS | | #6

    The utilities aren't really bound by the NEC, they have a different set of design standards (NESC), and they also do everything under "engineering supervision", which can get around a lot of things.

    You may be able to swap out the lugs on your panel, otherwise what I would do is to use compression barrel splices in a nearby junction box to adapt the wire down to a size that will fit the lugs. I don't like mechanical splices for this sort of thing, compression is much more reliable. You can use heat shrink tube to insulate the finished splices, ideally with two layers.

    You would need at least 2.5" conduit for the 300MCM wiring. I would use 3". It will be easier to pull the cables in a slightly larger conduit. You'll want to use lube though for this long of a run. You'll find that wires pull easier in HDPE pipe than they do in PVC conduit though, since polyethylene is more slippery.

    It's prefered to have the neutral sized the same as the two "hot" conductors here, although you'd probably be OK from a code standpoint sizing the neutral from the ampacity chart alone and not allowing for volt drop (which would allow for a 4/0 neutral on a 200A service). This may be frowned on by your locality though, and they may want you to show the calculations. You'll have to decide if the cost savings is worth the hassle, and it's probably only a few hundred dollars worth of savings.


    1. andrew84092 | | #9

      More sound advice here, see no reason not to adopt it.

      I agree about compression. I’ve made many compression lugs on marine DC cables up to 2/0. Even cut through one after using the hydraulic crimper - the strands get fused together, cold-welded, amazing to look at.

      Thanks again,


  7. walta100 | | #7

    Looks to me like the garage needs its own 200 Amp panel if the two car chargers are 60 Amps each and the heater draws 50 Amps. That puts you with a 320 Amp meter feeding twin 200 Amp panels with the solar connecting at the same point just after the meter.

    Just so you are clear most solar installs use “net metering” and when the grid goes down all solar production also shuts down, there are a few exceptions with batteries or generators but they tend to get expensive so the dedicated sub panel does not really have any benefit unless you are going small backup generator with auto transfer to key circuits.

    If you are ever going to want a generator speak now or forever hold your peace.


  8. exeric | | #8

    I concur with some of what Walta just said (comment 7). Transfer switch assemblies can almost be thought of as an electrical subpanel. But I think it might make more sense to put a Reliance transfer switch unit INSIDE the house, either the kitchen or a utility room. As was said, if you go for grid tied solar panels, they can't supply emergency power. However, several solar panels can be dedicated to backup power at minimal expense as long as they are tied in with the Reliance transfer switches. It is most convenient to use them, and to get the most use out of all your solar panels, if the transfer switches are located inside the house. It would make the most sense to only have them power the essentials: lights, refrigerator, microwave, ceiling fans, a few kitchen electrical outlets, and possibly a 120 volt heat pump water heater. Anything more would require too big an investment in batteries and too many solar panels dedicated to emergencies.

    Whether this would make sense depends somewhat on which part of the country you live in. Here in the West we expect outages in summer due to fires or rolling blackouts. Solar panels can handle that shortfall in a pinch. In colder climates where outages occur mostly in winter you might have to invest in a gas generator to supply the heavier loads and lower PV output at that time of year. Then it's not worth the trouble to put manual transfer switches indoors since the generator still has to be outdoors.

  9. andrew84092 | | #10

    Walter/Eric: Thank you, I understand your comments. I will have to make 200A work, even with 2 EVs, I will put in load-shedding devices if I have to.

    My plan was to use the 12K Sol-Ark inverter with battery input and grid-tied. This has a dedicated feed for an essential loads panel, it is only 50A but functions like a UPS. You can install a manual transfer switch to move essential loads back over to grid (if you are working on the solar system). You could also replace with an automatic transfer switch to move essential loads to the grid if the Sol-Ark unit goes down while you are away.

    I think I will back-feed the solar into the garage panel and make sure I get a 225A bus. With 200A main breaker I believe this will allow me 70A of back-feed (120% rule). I might need to move the 100A house panel into the garage, this then becomes a 50A essential loads panel (combined with a transfer switch) and everything else gets moved over to the 200A panel (except for the ADU).

    I think I need a new schematic.

    1. exeric | | #11

      The Sol-Ark is known and liked by many people as an all-in-one solution. It repurposes existing solar panels for both grid-tied and back-up use. That functionality doesn't come cheap though, either in complexity or cost. I tend to worry about that. I suppose that reveals my own natural inclinations more than anything else. You should be fine going that route.

  10. andrew84092 | | #12

    Thanks Eric. Yes, those are the trade offs. I also like KISS, but you have to like the functionality …

  11. Andrew_C | | #13

    Wow. Some of the users of this website are unbelievably generous in sharing their hard won experience and knowledge. Sometimes I'm astounded.

  12. andrew84092 | | #14

    Here is the new schematic with Sol-Ark and transfer switch. I didn’t realize that I can have a private electric meter can in my state, so I added that for the ADU, makes much more sense.

  13. Expert Member
    BILL WICHERS | | #15

    If you want to plan for a generator, I'd strongly recommend getting an ATS for the service and not one of the smaller manual subpanel-like units. It's much more convenient to have everything switch over with an ATS. Load shed kits can help to lock out excessively large loads (EVs and electric heaters) to keep the generator within ratings. Note that if you go with an ATS here, you could actually get by with a "regular" one (not service rated), since you have that remote main disconnect. I would still use a service rated one here though, because having that local main breaker to shut everything off -- even if only for testing -- will be a lot easier than walking a few hundred feet to the main and back any time you need to do anything.

    You might try a commercial panel for that garage subpanel. The Siemens commercial panels that take bolt-on breakers have 250A bus standard, which might be good for you. They aren't all that more expensive than "regular" panels. I would make sure to get one with copper busbars though, since there is almost no cost difference between their copper and aluminum busbar options, and copper is better.

    BTW, EV chargers and electric heaters will have breakers sized according to the "80% rule", so a "60A" circuit will actually likely max out at a bit under 48A. The actual load will depend on the car though, since it is the charger in the car that will actually determine how much current is pulled through that "charger" on the wall. You need to size the feeders to that subpanel with the EV chargers and heaters according to the 80% rule too, but once you get to the 200A main panel, the EV chargers and heaters are only a portion of the total load, which helps you out in terms of total sizing with continuous vs non-continuous loads. The code defines "continuous" as 3 hours or more, which will typically include EV chargers, and should apply to heaters as well.


  14. andrew84092 | | #16


    I’ll look into that 250A bus panel, that could be perfect if I were to parallel a second Sol-Ark in the future.

    Yes, 80% rule, 50A breaker and wiring required for a 40A continuous load device (my current EV charger).

    I agree about benefits of whole-house ATS but a large generator is not part of the design and the whole-house switchover does not really play well with the Sol-Ark where essential loads are always UPS protected and fed from the inverter.

    The Sol-Ark does have a 40A input (and a gen-start output) for a small generator. A MTS is part of the design, this feeds the essential loads panel (ELP). But, it is a big disadvantage to have to decide upon and then hard-wire your essential branch circuits.

    For some time, I have been thinking about doing two side-by-side surface mount 125A main house panels above a wiring gutter (in the utility room). Leave enough length in all branch circuit feeder cables so they can be easily moved between panels in the future. One panel is the ELP, the other is remainder of main house loads panel.


    1. Expert Member
      BILL WICHERS | | #19

      You have to size the wire for the breaker. If it's 40A load, 80% rule says 50A breaker, and ampacity chart says that needs #6 copper wire if NM cable, or #8 copper if in conduit.

      I would use 200A panels, not 125A panels. You can parallel several 200A panels off of one 200A feeder if you want to, because the remote breaker provides overcurrent protection. If you want to be able to rearrange circuits between the panels, I would run a trough over the top of the panels (or underneath), connect all the wires to the trough, then connect the trough to each panel with several 2" close nipples, or chase nipples if the trough doesn't interfere with the cover on the panels. This way you can reroute the wiring in the trough and not have to physically move the cable itself outside of any enclosures. This is pretty commonly done commercially when you have a row of several panels.

      Note that with the commerical panels, you can put a main breaker in a panel, then lugs at the other "end" of the busbar at the same time, and use those lugs to feed a second main-lug panel. The one main breaker works for both panels. I've done this before when I needed more than 42 spaces in a panel.

      BTW, when you get your panel(s), try to get some that have the same number of spaces as circuits. This would mean they'd say something like "40 circuit, 40 space", not "40 circuit, 30 space". The "40/30" panel would need ten skinny breakers. Try to avoid using skinny breakers if at all possible.


      1. andrew84092 | | #25

        “I would use 200A panels, not 125A panels. You can parallel several 200A panels off of one 200A feeder if you want to, because the remote breaker provides overcurrent protection”

        I had not realized this as a code-legal possibility, but it makes perfect sense. Use a simple splitter box to turn a single 200A feed into 2 or 3.

  15. Deleted | | #17


  16. andrew84092 | | #18

    Updated schematic shows the gutter concept

  17. walta100 | | #20

    Given that you are paying for the 225 feet of main cable you may want to consider going with a 208 3 phase service that will allow you to use smaller gage wires to power the same loads If 3 phase is available.

    I still suspect the fire department will require a solar disconnect very close to the power meter.


    1. Expert Member
      BILL WICHERS | | #22

      That only works if you have three phase loads (which usually means motors). For single phase loads, you really don't gain anything, and you potentially introduce some complexities on the neutral, which is why you are not permitted to reduce the size of the neutral conductor in many cases. For typical single phase residential loads, three phase doesn't really offer any advantages, but it does mean you need a commercial three phase panel, and three phase breaker, all of which add $$$ to your installation.

      If you were thinking "run three phase 480v", you could actually get 480 volt single phase service, and run much smaller wire, but you'd be paying for your no-load transformer losses all the time. Those losses will gradually cancel out the savings on copper in the form of increased electric bills over time.

      You may be able to solve the entire "solar disconnect" issue by putting a "safety switch" (a big shutoff switch) on your house. Such a device can then be used as a shutoff to keep fire department people happy, and it doesn't have to do over current protection, which keeps it cheap.

      A remote shutoff should work too. I think there are some requirements for those, which implies they are acceptable, but I've never installed one so can't give any real specifics here.


  18. andrew84092 | | #21

    Thanks Walta, I considered 3-phase, but it’s not available. I need to confirm about that solar disconnect. It would be a hefty extra expense to route another set of feeders 450ft there and back, really a deal killer. I wonder if they would allow a low voltage switch that trips a relay in the garage?

    1. Expert Member
      BILL WICHERS | | #23

      Look into EPO (Emergency Power Off) systems. These tend to be large contactors (fancy way to say "big relay") that are remotely operated. These are what kill the power to things like wood shops when someone hits the big red "OFF" buttons on the wall. You see these in school shops all the time.


    2. exeric | | #24

      You wouldn't need to run the solar disconnect (technically the solar AC disconnect) 450 ft. In a typical solar installation, there is a "combiner" that takes all the parallel power lines from the solar panels, either raw DC or 240v ac from microinverters. This combiner can be integrated with other functions so the SolArc might function as that combiner. I don't know. Typically, the combiner has its own CB for each branch coming into it before they are joined up. This stops the failure of one of the solar branches coming in from tripping off all of the solar.

      After that the separate lines are combined into one 240v output circuit - hot, neutral, and grd. That output should go to the AC disconnect switch that is separate and visibly placarded as such. Only the "hot" wires, red and black, go through the 2-pole switch. Then the wires go from the output of that switch to the main panel right at the house. The AC disconnect box should be no more than a few feet from the main panel right at the house. All you're doing is interrupting a circuit that would already be there with a disconnect switch.

      Again, I'm guessing that the Sol Ark might function as a combiner in this case. Because the Sol Ark is essentially uninterruptible if grid power disconnects you may need a separate AC disconnect for that power that gets turned back on. I'm not sure how it would work in such a system. I'm sure there will be documentation from the manufacturer that prescribes best practices in such a case. You should go by that for such a special case.

      1. andrew84092 | | #26

        Thanks Eric. I’m working my way through the Sol-Ark manual. You have correctly identified the issues (including the UPS, which is a second AC output from the Sol-Ark which would also need to be disconnected). The SOl-Ark has a Rapid Shut Down input, I just have to verify with the City whether the shut-down button has to be near my pedestal meter or whether its OK on the side of the house. Either way it’s going to be a low amperage circuit so should work out.

  19. andrew84092 | | #27

    Thanks to BIll’s input, I’ve also rethought the panel layout a little and with just one more 200A SE transfer switch I can provide a lot more current and future flexibility. It’s still a work-in-progress but I will post it again, maybe it can also help someone else out

    1. andrew84092 | | #28

      Attached is, I think, the optimal strategy (for me). It provides a whole-house backup in addition to the UPS backup. Load management when in whole-house backup mode (200A transfer switch set to backup power) would be done manually by selectively energizing circuit breakers (e.g. the garage door breaker).
      Whether this optimal strategy survives the budgeting process is another matter.
      Thank you again for all the useful comments, really made me think it through.

      1. andrew84092 | | #29

        Not sure attachment was added, so I’ll reattach

        1. Expert Member
          BILL WICHERS | | #30

          You will probably need a contactor to lock out the solar setup so that it doesn't "see" power on it's input that is coming from it's own output when the ATS is in the "emergency" position.

          Your 100A ATS looks odd. It is customary to show ATSes in diagrams as being connected to the "normal" source, which is usually the utility. That 100A looks to have the UPS output connected as the normal source? Is that really what you want? I could see this ATS as acting as a sort of "transfer if the UPS function of the solar system fails, but otherwise power the critical loads from the UPS function all the time" sort of setup, so maybe you intended it this way?

          You will need to be careful with this system while running on UPS. The reason is that your ground-neutral bond is at the remote meter pedestal, but when the UPS is connected where is the ground-neutral bond? Is there one? You have two code rules you have to follow here: one is that there MUST be a ground-neutral bond at the first disconnect, which is the 200A breaker in that remote meter pedestal. The second issue is that there can be ONLY ONE ground-neutral bond in the system, which should be at that main disconnect. If you have a situation where you would have multiple bonds simultaneously connected, that's a problem. Commercially, we deal with this by using ATSes with "neutral throwover", which means they have an extra pole in the switch to switch the neutral. I just installed one of these this past saturday, and it's because when the system goes to generator, the bond is at the breaker in the generator. The reason for that site is that the facility has a 1,200A 480V feed, and code requires a GFI on 480V circuits over 1,000A. The four pole ATS with neutral throwover is required to allow for the proper functioning of that GFI. In your case, the UPS could be the issue. You need to be careful here.

          I would also recommend you re-draw your diagram in left-to-right format, so the service starts in the upper left, then works towards the right, which branch circuits coming down from top to bottom. That is more conventional, and much easier to read. Your diagram is a bit of a clustered circle type of arrangement, which is much more confusing, which makes it easier to miss details.


          1. andrew84092 | | #31


            Your first paragraph: You are absolutely correct, didn’t catch that, maybe because my diagram has now become a confusing mess (initial drawing was based on site orientation and it just grew from that).

            Your second paragraph: Yes, that is how Sol-Ark is intended to work, normal position is for critical loads to be fed full-time from the UPS (and pass-through) 50A Sol-Ark output. The 100A transfer switch is just there in case the Sol-Ark fails (or for maintenance).

            Neutral bond: absolutely, I understand the concept, have to make sure it gets implemented in whatever 200A transfer switch I choose (and I’m thinking it would be a manual switch, I still have the UPS output and don’t want the 50A breaker tripping when house not occupied).

            I will redraw based on your input (and convention).


          2. Expert Member
            BILL WICHERS | | #32

            If you go looking for a transfer switch with neutral throwover, keep in mind that a regular "three pole" switch isn't really right for a residential transfer switch with a switched neutral. In a proper transfer switch with neutral throwover, the contacts in the neutral switch mechanism break last (after the two hots are disconnected), and make first (connect to the other side before the two hots connect). This is done so that you never energize the hots without the neutral being connected. This is very important for safety and for proper voltage for your equipment. Don't cheap out here.


  20. andrew84092 | | #33

    Thank you. I see the necessity of this. There are now many “boxes” on my diagram that are over $1000 each (some much more). For me it’s the ultimate functionality, now it has to pass the cost-benefit and within-budget tests …
    But first, it’s the pedestal meter base (scheduling this with Utility today) and a temporary 50A service down to the house construction site. For this I am planning on using 190ft #6-3C w/Gnd Cu (rated for underground conduit and inside) with an RV-type remote pedestal panel (total circuit VD 3.86%). Copper is pricey, but I can repurpose the #6 inside the house.

    1. Expert Member
      Akos | | #34

      What you have sketched up seems too complicated, I would look at simplifying it. Never mind the install cost, somebody needs to configure and fix this down the road. When it comes to this type of install, KISS is your friend.

      If your utility power is reliable, an ATS is overkill espeically if you have battery backup. Plug in generator with manual transfer.

      For net metered solar, you want your PV on grid tie inverters. Going through MPPT to battery, battery to grid adds extra conversion losses. Plus your can't go with micro inverters which makes the all too common partial shading losses much worse.

      The best bang for your dollars is a grid tied battery inverter that can do frequency shifting and micro inverters that can properly curtail in response to that. You still need a way to disconnect from the grid to run during a power outage, most inverter manufactures now offer a solution for this.

      Our code allows for the disconnect to be at a distance from the meter as long as the unfused feeder is bellow ground and outside of the house. I would put the disconnect at the house to simplify install.

      If your PV rules require a PV disconnect at the meter the more reason look at micro inverters as usually an RSD is not required for those.

  21. andrew84092 | | #35

    Thank you Akos, I understand your critique.

    Sol-Ark does have a new one box hybrid inverter solution, the 15k. It’s not quite 15k in cost, more like $8k!, but it looks impressive. It has 200A pass-through, so the one-box doubles as your main ATS, with inputs: generator, battery, PV (both DC and AC coupled, ie micro inverters). I’ll attach their schematic to show the general idea. It gives me the functionality, although I would need to add some load shedding.

    Having said all that, for what this is going to cost I have my doubts as to whether it’s all worth it. And yes, it’s tempting just to add an MTS and generator.

    And putting the service disconnect on the side of the house does seem to make things easier. I checked with the Inspector and he said that’s fine. It is the Utility who wants it at the meter pedestal.

    1. exeric | | #37

      "And putting the service disconnect on the side of the house does seem to make things easier. I checked with the Inspector and he said that’s fine. It is the Utility who wants it at the meter pedestal."

      Are you sure that "service disconnect" and "solar AC disconnect" aren't being confused here? It seems to me all you would need is a general service disconnect at the meter. This would not interfere with having a separate AC solar disconnect right by the main panel at the house. Both disconnects would be manual and are there simply to comply with safety requirements when any automatic features go ka-blooey. (technical term.)

    2. exeric | | #38

      Referring to my #37. There is always a main breaker in the main panel that is at the house. In our jurisdiction they allow that breaker to serve as the main service disconnect. If your jurisdiction does not allow that then you might need another separate service disconnect at the house to satisfy both your inspector and the utility. I'm thinking that one of the different agencies is confused over this problem as it would clearly be redundant to have to have both.

      1. andrew84092 | | #39

        Well, there certainly is confusion. But I’ve talked to Inspector and Fire Chief. And yes, it’s fine to have the solar disconnect down at the house, still awaiting an answer as to whether it can be inside or has to be on outside wall of house.

    3. Expert Member
      Akos | | #40

      "It is the Utility who wants it at the meter pedestal"

      I would double check with the utility. There is a big difference between the tech liking a disconnect at the meter vs the disconnect must be at the meter. Asking for a link to the relevant rules is a good way to filter these. They will have a PEng stamped document outlining the connection requirements. Usually utility requirements end at the meter base, after that it is the jurisdiction of the electrical inspector.

      DC couple PV with string combiners works well for something like a ground mounted array in a field with no trees or shading. Even there, with snow it is better to split the top and bottom of the array. For a roof setup with plumbing vents, chimneys, dormers and trees you want micro inverters. More efficient and less issues with shading.

      Most micro inverters will not sync to a generator reliably, so if you need to run on a genny a lot, a DC coupled system is better.

  22. andrew84092 | | #36

    I was just looking through the other schematics for the 15k and noticed that you cannot have both AC-coupled PV and Gen inputs at the same time. The AC-coupled uses the Gen breaker. So if you want a generator you are limited to DC-coupled solar (or more boxes).

  23. Expert Member
    BILL WICHERS | | #41

    If the cable from the meter to the panel is more than 6-10 feet (I forget the exact length since I don't do much residential, but it's in this range) you have to have an OCPD at the meter, then use 4 wire (hot/hot/neutral/ground) cable from there to the main panel. This is a code requirement.

    OCPD means "OverCurrent Protection Device". It can double as the disconnect, but disconnects don't necassarily have to be OCPDs. An OCPD is a fuse or circuit breaker here, a disconnect is just a switch (or a pullout fuse block). This is an important distinction. In mmy example earlier, you can have the OCPD at the meter base where it is required, and use a SAFETY SWITCH (a big switch) as a disconnect at the house to keep within the rules for solar stuff or any other requirement for a shutoff within some distance of a structure. The OCPD can also act as an additional shutoff if you also have a safety switch, so no problem if you need multiple disconnects BUT -- you're not supposed to have more than 6.

    So what this means is you MUST have the OCPD at the pedestal, to protect the long run of wire from there to your main panel. This can also be a service disconnect, but it's not very convenient due to the distance. This is why I'd recommend putting a second disconnect at the house, which could be a main breaker in the panel, or could be a switch on the house somewhere. Either works for the purpose of shutting off all power to the structure.

    BTW, for your temporary run during construction, don't waste money on copper cable. Use aluminum SER cable, which is what everyone uses for temporary stuff like this. SER cable has hot/hot/neutral insulated wires of the same size, and a slightly smaller uninsulated ground wire. It's commonly used for permanent runs from OCPDs at meter bases to panels, but it's also commonly used as a big "extension cord" for temporary power stuff during construction. The usual way to run it is to support it on 2x4 "poles" with caution tape hanging from it. It's cheaper than copper, and it will work just fine. I would use #2 aluminum SER here, which should keep voltage drop reasonable. I would put an OCPD at the meter of 100A or less to protect the wire. You can use a regular ol' panel at the construction site, but if it's outdoors it needs to be drip tight. Most people use one of the 8-20 space panels for this. Remember that the outlets it feeds on the jobsite are supposed to be GFCIs! I would also drive in at least one ground rod at the job site and tie it into the ground bar on this panel (which also needs to tie back to the main ground at the pedestal), since you have such a long run of wire from the main ground to the jobsite.


  24. andrew84092 | | #42

    All extremely helpful, thank you. I was wondering about the giant extension cable, I guess they are used at outdoor events all the time.

    I hear you on benefits of micro-inverters. And a large battery bank does not really make any economic sense for me, unless that large battery bank happens to be located in an EV and the manufacturer allows you to draw from it.

    1. Expert Member
      BILL WICHERS | | #43

      Portable power cable is usually a mix types SO and W flexible/portable power cable, sometimes with color-coded "camlock" connectors which are seperate connectors for each wire in the cable. The cable itself is usually black. This type of cable is nice and flexible, but also VERY expensive (comparatively), and isn't really needed on a "once and done" type of setup like temporary power on a construction site. SER cable is normally a light gray in color, and it's fairly stiff. You wouldn't normally see SER used on something like a fair or outdoor festival that needs to setup and tear down their equipment lots of times every season. Different materials for different uses here.

      The primary reason to use SER is that it's the cheapest thing that will work. Remember that when your project is done, and not even "all the way done" -- just enough for permanent power to go live, all that SER cable is either going to be given away to your electrician for possible use on a future project, or set to the scrap yard where the aluminum will ultimately be stripped out and reprocessed. There is no need for anything fancier than necassary here since it's going to get torn out in a relatively short time.


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