ADU Panel Upgrade in Sacramento
Almost everything written about ADU electrics is about the panel. The thing that actually delays Sacramento ADUs is the utility, and SMUD’s own published figure for its part of the process is four to six months from application to occupancy — running separately from the city’s planning and building timeline. If you have not started that application, you are already behind. Here is the sequence, and where the time actually goes.
Where the time actually goes
Talk to SMUD before you finish the drawings
This is the City of Sacramento’s own advice on its ADU guidance, and it is worth taking literally. The city tells homeowners it is highly advised to coordinate with SMUD early in the planning stages, to identify constraints that may dictate the site planning and layout of the ADU.
Read that again, because it is not a politeness. Where the transformer is, where the existing service runs, whether the supply is overhead or underground, and how far the ADU sits from all of it can change where the building goes on the lot. People discover this after the architect has been paid, which is the expensive order to discover it in.
The practical version: get an electrician and SMUD looking at the site before the design is fixed, not after the permit is filed. It costs nothing at that stage and it is the single cheapest hour in the whole project.
Which of SMUD’s two paths you land on decides your timeline
SMUD sorts incoming projects into two routes, and which one an ADU falls into matters more to the schedule than anything your electrician does.
- Meter and service. For work that will not require upgrades or additions to SMUD’s existing infrastructure. This is the quicker route — the one where the constraint is paperwork and inspection rather than construction.
- New SMUD construction required. For projects that need SMUD to add or upgrade infrastructure: a transformer that cannot carry the new load, a service extension to reach the ADU, conductors that need replacing. This is where months live.
Nobody can tell you from a web page which one you are on. It depends on your transformer, your existing service and where the ADU sits. It is exactly the question the early site visit answers — and it is the question to put to SMUD first, because the answer changes your whole programme.
On the quicker route, SMUD publishes two figures worth holding onto: a SMUD engineering designer is assigned within one business day of the application and fees being received, and SMUD’s own work is typically completed within seven business days of the meter panel inspection approval. Those bookends are fast. The middle is not.
Four to six months, and why it is separate from the city’s clock
SMUD’s ADU guidance puts the typical timeline from application to building occupancy at four to six months. The important word is “typical”, and the important structural point is that this runs alongside the city’s planning and building process, not inside it.
So an ADU has two queues: the City of Sacramento’s, which gates your permit, and SMUD’s, which gates your power. People plan carefully for the first and discover the second in month three.
The order that works is unglamorous: talk to SMUD during design, apply as early as SMUD will accept the application, and treat the electrician’s work as something that slots into the utility’s schedule rather than the other way round.
If you take one thing from this page: the application date, not the build date, is what determines when your ADU gets power. It is the only part of this entirely within your control, and it is free to start early.
One meter or two?
SMUD’s ADU handout states that a duplex meter installation is usually required for most ADU situations — that is, two meters in one arrangement rather than a single meter serving both dwellings.
That has consequences beyond the hardware:
- The service equipment changes. A duplex meter arrangement is not the panel you currently have with a sub-panel hung off it. It is usually a new service entrance, which is why ADUs so often turn into service upgrades.
- Billing separates. Two meters means two accounts, which is what most people building a rental actually want — the tenant pays their own power.
- SMUD’s requirements govern the physical layout. SMUD’s service specifications set minimum clearances between meter sockets, and SMUD staff make the final connection between their wiring and yours. This is not a part of the job an electrician can improvise around.
“Usually” is doing real work in that sentence. Some ADUs are served from the existing service, and SMUD decides. What you should not do is assume the cheaper arrangement and design around it.
Will the existing service carry an ADU at all?
An ADU is not an extension. It is a second dwelling, with its own kitchen, its own water heating, its own heating and cooling, and — increasingly in new Sacramento ADUs — all of it electric.
A 100-amp service gives 80 usable amps under the continuous-load rule, and a typical older Sacramento house has already committed most of that to its own air conditioning, dryer and kitchen. There is rarely a second dwelling’s worth of capacity sitting spare.
Which is why the honest answer to “do I need a panel upgrade for my ADU?” is: usually, and a load calculation is how you find out rather than a rule of thumb. The arithmetic, and the cases where a sub-panel or a smaller service increase is the right answer, are on our 200-amp panel upgrade page.
Two things worth raising with your electrician early, because both change the number:
- An all-electric ADU — heat pump space heating, heat pump water heater, induction hob — draws more from the service than a gas-equipped one, but it is also what SMUD’s incentive programmes are built around.
- An EV charger at the ADU, now or later. Adding it to the plan costs far less than adding it to a finished building, and the charger size changes the load calculation. Our EV charger page covers what each size actually needs.
The Sacramento permit path
Inside the City of Sacramento, the sequence has a gate in it that catches people out: planning approval, or an approval for concurrent review, must be obtained before you submit the building permit application to the Building Division. You cannot start with the building permit.
On the electrical side, the plan set has to include an Electrical Layout Plan as part of the complete submittal. That is a drawing, not a note on a page — another reason the electrician belongs in the project early rather than at second fix.
One more rule that frequently changes an ADU design, and is worth knowing even though it is not electrical: fire sprinklers. A detached ADU can be exempt where the main home is not sprinklered and the ADU, not counting the garage, does not exceed 1,200 square feet. For an attached ADU the exemption applies where the existing home is not sprinklered, the addition is no more than 50% of the original structure, and the total including the addition does not exceed 3,600 square feet.
Outside the city limits the counter changes. Sacramento County runs its own Building Permits and Inspection Division, and Elk Grove, Folsom, Rancho Cordova and Citrus Heights each run their own. Requirements are broadly similar; the forms and the queue are not.
What the electrical side costs
These are the ranges homeowners here commonly report and that Sacramento electricians publish on their own sites. They are context for reading a quote — not a quote, and not an offer.
| Scope | Typical Sacramento range | When this is you |
|---|---|---|
| Sub-panel to the ADU from an existing service with capacity | $1,200 – $3,000 | Rare on an older house, but the cheapest outcome when it applies. |
| Upgrade to 200A with new meter-main combination | $3,500 – $6,500 | The common outcome when the existing service cannot carry a second dwelling. |
| Service upgrade including new mast and service conductors | $5,000 – $9,000 | Overhead service where the mast is undersized or corroded. |
| Underground service, trenching, or the panel relocating | $7,000 – $14,000+ | Common where the ADU sits at the back of the lot. |
What moves these numbers on an ADU specifically is distance. A detached ADU at the back of a Sacramento lot needs a feeder run to it, and if that run is trenched under a driveway or mature landscaping, the trench is a meaningful part of the electrical bill. Walk the route before you compare quotes. The full breakdown of what moves a quote is on our panel cost page.
What SMUD does not publish — and why we are telling you
We would rather say this plainly than imply we know more than we do.
SMUD’s public ADU material gives the four-to-six-month timeline and the duplex meter expectation. What it does not publish, as of this review, is:
- A minimum service size required for a property with an ADU
- Connection or application fees for an ADU service
- A clear rule for when the existing service must be upgraded versus kept
Those three answers come from SMUD directly, for your specific address, via the application and a designer. Any page quoting you a confident number for them is guessing, and you should treat that as a signal about the rest of the page.
If the answers matter to your budget before you commit — and on an ADU they usually do — get the SMUD application in early enough that the designer’s answers arrive while you can still act on them.
Common questions
Do I definitely need a panel upgrade for an ADU?
Not definitely, but usually. An ADU adds a second dwelling’s worth of load — kitchen, water heating, heating and cooling — to a service that was sized for one house. A 100-amp service has about 80 usable amps and an older Sacramento home has generally committed most of them. A load calculation settles it; a rule of thumb does not.
Can the ADU just run off a sub-panel from the house?
Sometimes, where the existing service genuinely has capacity. But SMUD’s own ADU guidance says a duplex meter installation is usually required for most ADU situations, which generally means new service equipment rather than a sub-panel. Worth asking SMUD rather than assuming, because designing around the cheaper answer and being told otherwise is an expensive reversal.
Will the tenant get their own bill?
With a duplex meter arrangement, yes — two meters means two accounts. That is usually what people building a rental want, and it is one of the reasons the duplex arrangement is the norm rather than an imposition.
How early should I start the SMUD application?
As early as SMUD will take it. Their part typically runs four to six months from application to occupancy and runs separately from the city’s process, so an application filed when the build starts is an application filed months late. There is no penalty for being early and no way to buy the time back later.
Does the ADU need fire sprinklers?
Not always. A detached ADU can be exempt where the main home is not sprinklered and the ADU, excluding the garage, does not exceed 1,200 square feet. Attached ADUs have their own thresholds. It is not an electrical question, but it changes the design and therefore the electrical layout, so it belongs in the same early conversation.
My panel is a Federal Pacific or Zinsco. Does that change the ADU plan?
It simplifies it, in a sense — the panel is coming out regardless, so the question becomes what to put in rather than whether to touch it. It also means your insurer may already have a view. See our pages on FPE and Zinsco replacement and Zinsco panels specifically.
Find out what your service will take before the drawings are fixed
Tell us where the ADU is going and what panel you have — a photograph of the panel label is the single most useful thing you can send. We will connect you with a CSLB-licensed C-10 electrical contractor covering your address. There is no charge to you, and no obligation to proceed.
Last reviewed October 2026. SMUD timelines and requirements, permit rules and city ADU policy all change — this page is dated so you can see how current it is.
About this service. Sacramento Electrical Panel is a free referral service that connects homeowners with independent, CSLB-licensed electrical contractors. We are not a licensed contractor, we do not perform electrical work, and we do not provide quotes, estimates or contracts for electrical work. Any price you are given comes from the contractor directly, and any contract you sign is between you and that contractor.
Cost ranges on this page are general information about the Sacramento market and are not an offer or an estimate. Timelines and requirements are summarised from SMUD’s and the City of Sacramento’s published guidance and are typical figures rather than commitments to your project — confirm both with SMUD and your local building department. Always verify a contractor’s licence status and classification at cslb.ca.gov before signing anything or paying a deposit.