ADU Electrical in Santa Clara County. Sub-Panel, Feeder, and Full Rough-In.

Yes. In virtually all cases an ADU requires a dedicated sub-panel. The most common approach is a sub-panel fed from the main home's panel, sized at 60A to 100A and installed in or near the ADU. This works for attached ADUs, garage conversions, and detached ADUs within about 100 feet of the main panel, provided the main panel has sufficient capacity to support both structures. A load calculation is always required to confirm this. For larger ADUs, units well beyond 100 to 150 feet from the main panel, or projects where independent tenant billing is the goal, a fully separate service with its own utility meter and main disconnect may be the better path. Cali Rollin Electric performs the load calculation during the free estimate to determine the right approach for your project.

Usually not, and for many ADUs a city cannot require one. Under California Government Code Section 66324 (recodified in 2025 from the older Section 65852.2), a local agency, special district, or water corporation cannot require a new or separate utility connection, or charge a related connection fee or capacity charge, for an ADU created within an existing home or accessory structure. Two carve-outs apply: an ADU built together with a brand-new single-family home, and an ADU that is separately conveyed. For other ADUs, typically new detached construction, an agency may require a separate connection, but the fee has to be proportionate to the unit's burden based on square footage or drainage fixture unit values and cannot exceed the reasonable cost of providing the service. In practice you have three choices: a shared meter with the ADU on the main home's existing service, a private sub-meter that tracks ADU usage for cost-splitting, or a fully separate utility service with its own account and bill. Cali Rollin Electric handles the utility metering application and coordination on your behalf.

Yes, and the cost argument is overwhelming. Adding an EV rough-in during the ADU build costs roughly $500 to $1,200 at Cali Rollin Electric: the conduit stub, pull wire, and a dedicated circuit reserved in the sub-panel. Adding a Level 2 charger later as a standalone project, once the walls are closed and the hardscape is poured, costs significantly more. New ADU construction with an attached private garage is generally required to be EV-ready under the California Green Building Standards Code, meaning raceway plus reserved panel capacity for a future 240V charging circuit, and your plan checker confirms which section applies to your configuration. Even when it is not strictly required, the construction window is the cheapest possible moment to future-proof the parking space. Every ADU project we handle includes this conversation before the rough-in inspection is scheduled.

ADU electrical is almost never a standalone permit. Across Santa Clara County jurisdictions the electrical scope rides inside a larger ADU building permit package alongside building, plumbing, and mechanical, submitted under a second-unit or ADU application type. Building departments in the county generally ask for the same supporting documents: an ADU property owner declaration, an address assignment request so the unit gets its own address, a water and fire flow letter from the serving water provider, and Title 24 energy compliance documentation under the current California Building Standards Code. Plan submittal to permit approval commonly takes two to three months. ADU permits are ministerial by state law, so there is no discretionary hearing, which means the calendar is driven almost entirely by how complete and correct the package is at submittal. A resubmittal for an undersized feeder or a missing load calculation can add weeks. Cali Rollin Electric handles the electrical scope inside that package and works directly with your general contractor and the building department through final inspection.

The entire electrical scope, from load calculation and permit drawings through final inspection sign-off. For ADU projects Cali Rollin Electric handles the load calculation for the main home and the ADU, electrical plan drawings for the permit package, trenching coordination for underground conduit to detached units, sub-panel selection and installation, all branch circuit rough-in wiring, Title 24 and storage-ready provisions, AFCI and GFCI protection throughout, EV charger rough-in at the parking location, rough-in and final inspection coordination, trim-out and panel labeling, and the utility meter application if a separate service is desired. You do not need to manage separate electrical and panel contractors or translate between trades. We work directly with your general contractor, your ADU designer, and the building department.

There are three honest answers depending on what the NEC 220 calculation shows. If the panel is sound and just short on calculated capacity, a code-listed load management device can hold the home under its service rating so the ADU sub-panel can be added without a service upgrade. If the service itself is genuinely undersized, a 100A to 200A main panel upgrade is the real fix, and we scope it together with the ADU so it is one permit process and one utility coordination effort rather than two. If the existing panel is a Federal Pacific or Zinsco, it gets replaced regardless of capacity because that is a safety issue, not a capacity issue. We tell you which situation you are in before you commit to a scope.

Quite different, and it usually favors the garage conversion on cost. A garage conversion is typically attached or very close to the main panel, so the feeder run is short, there is often no trench at all, and the existing garage circuits can sometimes be reworked into the new unit. The catch is that garage wiring in older homes was rarely built for a dwelling: expect to add kitchen small-appliance circuits, bathroom and laundry circuits, AFCI and GFCI protection throughout, receptacle spacing that meets NEC 210.52, and interconnected smoke and CO detection. A detached ADU adds the trench, the underground feeder, a disconnect at the structure, and its own grounding electrode system, which is where the extra several thousand dollars usually goes.

An ADU is a full dwelling unit for code purposes, so it gets dwelling-unit circuit requirements rather than accessory-building treatment. That means at least two 20A small-appliance branch circuits for the kitchen counter and dining areas, a dedicated 20A bathroom circuit, a dedicated 20A laundry circuit where laundry is provided, dedicated circuits for fixed appliances such as a range, heat pump water heater, or mini-split, GFCI protection at kitchen counters, bathrooms, laundry, outdoors, and other NEC 210.8 locations, AFCI protection per NEC 210.12, receptacle spacing per NEC 210.52, and interconnected smoke and carbon monoxide alarms. Circuit count is the single biggest driver of the interior electrical price, which is why a compact studio and a two-bedroom unit sit at opposite ends of the $6,000 to $14,000 range.

The electrical labor itself is a small share of the calendar. On a typical 400 to 600 square foot unit, the feeder and sub-panel take one to two days, interior rough-in takes two to four days, and trim-out (devices, fixtures, panel labeling) takes another one to two days, with inspections in between. What actually sets the schedule is the permit package (commonly two to three months from submittal to approval), the general contractor sequence, and, if the ADU is getting its own utility service, the utility design and meter-set timeline. That last item is the one that surprises people, which is why we ask about metering at the first conversation rather than at rough-in.