ADU builders
ADU electrical panel upgrade: do you need one?
By the HyreADU research desk. Last checked .
The short answer
An ADU electrical panel upgrade is needed only if a load calculation says the existing service cannot carry the house and the ADU together. There is no rule that an ADU needs a set number of amps. A licensed C-10 electrician or an electrical engineer runs the calculation under the California Electrical Code.
What decides it
The rating of your existing service, the house’s current load, the ADU’s planned appliances, and whether heating, cooking and water heating are electric. The calc adds them up under the code and compares the total with the service.
Why gas no longer saves panel space
Since the 2022 Energy Code took effect on 1 January 2023, a newly constructed single-family building that uses gas for heating, water heating, cooking or drying must still install a dedicated 240-volt circuit and reserve breaker space for each, so it can switch to electric later.
That applies to a newly built detached ADU, not to a conversion. See ADU electrical service upgrades.
Panel, subpanel or service upgrade
Often the answer is a subpanel in the ADU fed from the main panel. If the total load is too high, the service itself is upgraded, which involves the utility. Ask your electrician which one the calc supports, and get the utility’s requirements in writing.
What to do next: read the questions to ask an ADU builder, check what decides ADU cost, then tell us about your project. Matching is not live yet, so we reply with information, not a quote.
Get ADU optionsQuestions
Does every ADU need a 200 amp panel?
No. The load calculation decides.
Can the ADU have its own meter?
That is a utility and permit question. See ADU utility connection.
Who can do the load calculation?
A licensed C-10 electrical contractor or an electrical engineer.
Does an EV charger change the answer?
Yes, any added load goes into the calculation.
Sources
- California Energy Commission, 2022 Energy Code update summary. Checked September 5, 2026.
- California Energy Commission, 2025 Building Energy Efficiency Standards. Checked September 5, 2026.
- California Building Standards Commission, current codes. Checked September 5, 2026.
- PG&E Electric Rule 16 (service extensions). Checked September 5, 2026.
HyreADU is a publisher. It does not design, permit or build ADUs, has no partner builders, and gives no legal, tax or engineering advice. Rules vary by state and city; California rules are labeled as such.