I am working, with full permits from the city and future planned inspections of course, as an owner builder for the following projects:

  • construction of a detached garage, where I need a 200A service for:
    • car chargers
    • I have two large welders, CNC plasma cutting, big compressor, plus other 240VAC machines through VFD's
    • 18kW tankless electric heater, as I will have a full bathroom with sink and shower
  • swimming pool, where I need a 100A service for:
    • 240VAC pump
    • 5HP swimming current generator
    • (future) heat pump
  • BBQ area, where I need a 100A service:
    • 13kW tankless electric water heater
    • (future) if I decide to put in a ADU (basically my state allows the construction of a second dwelling in the lot)

In the list above, I only included the biggest stuff, not counting regular 110V outlets and lights.

Right now, at the meter (PG&E, California) I have one single breaker, and there is a subpanel in the garage that has the breakers for the whole house.

What I would like to do is to get rid of that and have a main panel next to (or integrated with?) the meter with the capability to feed few (6? 8?) "big breakers" that will in turn feed the subpanels mentioned earlier. (please correct my terminology here if it's inaccurate). All the utilities are buried and are fed from below.

I am quite confused by the selection of panels that I can find online and struggle to find real technical data, maybe with a picture, to understand what model would satisfy my needs. I want good products, that use copper, higher end if reasonable:

  • "main" panel with few breakers
  • 2 x 100A, outdoors rated subpanels
  • 1 x 200A, indoors subpanel

How do I choose one, or at least what are the elements I need to consider to narrow the solution space?

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    Seriously consider traditional tank water heaters instead of tankless. The on-demand power for tankless is insane. If you had gas it might be a different story. But consider that the 18kW tankless heater is roughly equivalent to two car chargers! A typical 50 Gallon "regular" heater will have 2 x 4500 W or 2 x 5500 W elements only uses a 30 A 240 V circuit. Your 18kW tankless will need more than double that. Aug 30 at 22:34
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    The new garage will be about 810sq ft with a 63sq ft bathroom. House is about 2800sq ft and I don't really have much going on there. Clothes dryer is gas, furnace and water heater gas too. No Air Conditoining. I am pretty sure I never use more than 50A for the house :) Aug 30 at 23:53
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    @ThreePhaseEel oven = 9.2kW at 240VAC, range = 11.6kW at 240VAC Sep 1 at 2:20
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    @ThreePhaseEel I have three 20A, 120VAC circuits that each serve three "double" outlets. There is a circuit dedicated to the dishwasher and another dedicated to the garbage disposal. Sep 1 at 4:13
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    @FreeMan OK I applied for a permit to lay gas pipe to the garage. I did not cancel the electric tankless idea, but at least I should have an easy way to upgrade to gas later. Sep 1 at 23:28

What you're looking for is called a "ranch panel"

Here is how a "Class 320" 400A ranch panel is laid out internally.

enter image description here

The major features are:

  • Meter
  • 200A breaker that goes straight to thru-lugs. The units are sold with this breaker location unpopulated, so different breakers can be fitted for 300 vs 400A service.
  • 200A breaker that goes to:
    • a) a "mini panel" of 8 spaces, giving 4 positions for 240V breakers up to 125A.
    • b) "Thru Lugs" which carry the 200A (shared with those breakers).

And yeah, expect 400A

I know you are pretty intense about wanting to skin this under 200A, but that's not gonna happen between the tankless heaters, which provision at 100%, and the EVSEs, which provision at 125%. And the pool equipment and the machines. And the ADU. And the house.

You are required to tell PG&E about the tankless heaters, so that will bring their attention to the situation.

I would send the dedicated 200A to the garage, on account of the tankless and EVSEs. The pool and BBQ area on 100A breakers (or 90A breakers) in the regular breaker space. The house on the shared thru-lugs. The house will require a 200A panel.

If you want to put the house on a third 100A breaker, that is fine, but shop carefully -- some panels have a 125A "stab limit" for the breakers opposite each other (sharing the same stab).


While copper bus stabs are fine, copper wires in these >100A feeders is a complete waste of money. A common novice mistake is harshly judging aluminum in heavy feeder wire, because of stuff they heard that they don't fully understand.

Plan on #1 aluminum on the 100A circuits (or the more readily available #2 aluminum if you downbreaker to 90A). 250 kcmil aluminum on the garage leg because of the high use factor and it not qualifying under 310.15(B)(7). 250 kcmil is the next size larger than 4/0. 4/0 can go to the house since it does qualify.

Dollar for dollar, your wisest overspend is buying extra-extra-large service panels. Breaker spaces are dirt cheap, laughably cheap, and they save you a lot of money later when you don't run out of spaces for add-ons. You need spaces, not "circuits". "Circuits" is a useless number because most circuits do (or soon will) require AFCI or GFCI breakers.

Another good investment for the discerning buyer of quality is EMT conduit. Harder to install, easier to upgrade, and far safer.

  • It took me a while to read everything here, thank you for the answer. Class 320 Ranch Panel Dedicated through lugs 200A to the garage 100A to the Pool 100A to the BBQ (future, possible ADU) 200A shared through lugs This is for the main-meter panel. Can I ask yo a favor: do you have a model number, from a reputable manufacturer, I can lookup and see for this case? Once I decide for a model the next challenge will be to source it Aug 31 at 20:09
  • "I know you are pretty intense about wanting to skin this under 200A" actually no, I do not really feel strongly about this. In fact, is there any reason why this should matter too much? Is a 320/400A service having more monthly fees? As far as I know, energy is metered independently of the size of the service, am I wrong? Sep 28 at 20:10
  • @AlessioSangalli Sorry for missing the earlier... also the assumption. Nah if you wanted to go 400A that could solve many problems. In fact, you could install 400A equipment today and only use half of it, so you'd be 400A ready. As far as electric tariffs, I can't even begin to speculate. That's a fast-moving target, because power companies have been casting about desperately for a survivable revenue model in an age of solar, PowerWall batteries, transmission line buildouts etc... and are putting fees in the strangest places. Sep 28 at 20:33
  • Assuming there are no relevant fees from the power company, the only reason not wanting to go to 400A is that equipment (panels) are bigger and so more expensive to buy? I'm just trying to understand if there is something I should be aware of here :) Sep 28 at 20:35
  • Yeah basically.... and 400A gear isn't bad right now, but under NEC 2020, apparently the dual 200A main breaker approach is being abolished requiring 1 master disconnect... They can't legislate cheap 400A breakers into existence. So unlike panels like the above, typically under $500, you are off into industrial land for very expensive gear. Sep 30 at 5:42

Your plans are pushing the limits of Class 320(!!!!)

Your problem is that you have a lot going on -- even:

  • disregarding the pool heat pump,
  • using gas for the tankless heater in the garage,
  • presuming that only one of the welder/cutters is running at any given time,
  • leaving no room for an ADU or extra shop tools,
  • assuming that the shop tools won't be running at the same time as the BBQ area tankless,
  • and using 40A circuits for both car chargers,

we wind up with a NEC computed service load of 81766VA, or 341A @ 240VAC. This leaves us with barely enough room for a 1200ft² ADU (the maximum size permitted under the California ADU law) with gas heat and a gas dryer; giving the ADU an electric dryer instead leaves us teetering on the brink of what that service can handle!

Once you start adding extras on, like air conditioners, more shop tools, a heat pump for the pool, or bigger car chargers, or migrating some of those existing gas appliances to electric, then you'll be needing to upgrade to a CT metered service, which is significantly costlier than even single-breaker Class 320 hardware. (A 5-jaw B-Line combination transformer cabinet/socket for underground service applications runs around $2700, and that's before you add the CT rack to the picture, or a 600A enclosed main device at another $2500 or so! This compares to a Siemens MC2442B1400SDS which runs about $2500 and includes the meter base, cabinetry, a 400A main breaker, and a 24-space 400A loadcenter interior.)

Furthermore, the future plans for an Accessory Dwelling Unit throw a wrinkle into this, as normally, one'd apply NEC 230.40 exception 3 to permit the service drop and meter to feed individual service-entrance sets for each building (house, pool shed/rack, garage/shop). However, the language in the exception was recently amended to only apply to single-family dwellings, so it's unclear if the presence of an ADU makes the exception inapplicable.

So, I'd take a harder look at getting two services from the utility, or at least setting things up to facilitate that in the future. That said, Harper's "ranch panel" approach, using a Siemens MC0816B1400SCS or equivalent with the dedicated 200A breaker feeding the garage and the "mini-panel" feeding the main house from its feedthru lugs atop providing breaker space for feeding the BBQ/pool panel, is reasonable except for the fact that the 2020 NEC curtailed the "rule of six" that those panels rely on, making them no longer legal for you to install come sometime next year (when the California Electrical Code gets updated to match the current NEC).

  • Wow thanks for the analysis. California updating to the new NEC means that even projects approved before that date will have to follow the new rules? The way it goes around here, projects move at an extremely slow pace, so I might have to look into the "rule of six" Also, following everybody's advice, I decided to axe the electric tankless and I got a permit already to get gas to the garage. I will also cancel the car chargers. The only problem at this point is hot water at the BBQ area. Given the low demand, I was hoping to skip the need for a gas heater, but I might have no choice. Sep 5 at 6:16
  • @AlessioSangalli -- not sure how approvals interact with Code adoption dates in Cali -- I'd keep one car charger in the plans, but axing the second is a good move Sep 5 at 11:59
  • I spent some time trying to read up the rule of six. Is there a solution to my situation (removing at least one tank-less electric and car charger) that will be compatible with the 2020NEC? I am quite confused by the whole thing. What if I have a main breaker in each sub-panel I install, in the garage, at the BBQ area, in the house? Sep 28 at 20:21

I suspect PG&E will only allow you one drop in and one metered input, and from that meter you will feed all the subs including the house. They will either upsize the existing feed to the garage to support 200A, or run a new main to the closest place convenient for them, and you will be responsible for back feeding all the panels including the house.

Actually, 200A seems light assuming your house is 100A itself with the shop equipment, the dual chargers, water heaters, and potentially another dwelling. I had a similar project (adding a shop and upgrading to 400A and moving the mains feed to the shop and making the house a 200A sub panel) see Sizing Ground wire for 200AFeeder to House and What component do I need to add my own "Private" electric meter

I must add that I am not in CA and not familiar with PG&E requirements. Lastly, PG&E has likely has a list of approved meters they allow or you will need to be get familiar with the PG&E Greenbook, yours will have to be Bottom fed by UG cable, and pay attention to the manual bypass test requirements.

6.2.2 Test-Bypass Facilities

For single-phase residential installations, test-bypass facilities may be provided, but are not required.

(followed by a list where test-bypass equipment IS required)

  • The garage is a new construction, I am trenching right now to lay the conduits. At this point in my project I do not see a need to change the location of the meter that is conveniently on the side of the house. Can you explain why do you think it might be useful to change the location of that? I'd just like to get a main breaker panel that can handle the current (power) and can host a PG&E meter, that according to my interpretation of the Green Book is a "ring" one. Aug 30 at 23:59
  • Code is code, a 30-40 or 320 panel will be enough, we don’t size the main completely on the size of the breakers , having been an apprentice in PG&e land they will put a second meter on a detached structure but under 400 amps peak it is waste of $ for the second service
    – Ed Beal
    Aug 31 at 3:23
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    Yeah I will not need everything at the same time. I either use the welder OR the plasma cutter OR the outdoors kitchen, so I wouldn't sum up all the services. When I mentioned 100A or 200Anfor the panel is to make sure the panel can support a peak. Second service seems excessive Aug 31 at 3:40
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    instead of using > blockquote to wrap a block quote, simply use the > as intended to indicate a block quote. ;) Also, one might assume that the quote comes from the PG&E Greenbook, but making that explicitly clear would be a good idea.
    – FreeMan
    Aug 31 at 12:15

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