Most garage ADUs in San Jose need somewhere between eight and fourteen dedicated circuits, depending on square footage and whether the unit includes a full kitchen. That number drives the entire electrical plan, and getting garage ADU electrical circuits right the first time saves weeks of permit back-and-forth with San Jose's Building Division. Our team at San Jose Garage Conversions has run electrical rough-in on dozens of garage-to-ADU conversions across the South Bay, and circuit planning is consistently where projects either move fast or stall out.
A garage conversion isn't a remodel with a couple of new outlets tacked on. It's effectively a small independent dwelling, and the 2022 National Electrical Code (adopted into California's electrical code) treats it that way once a kitchen, full bath, and separate living space enter the picture. That means dedicated circuits for major appliances, GFCI and AFCI protection in nearly every room, and a load calculation that has to satisfy both the utility and the city plan checker.
This guide walks through how our team sizes garage ADU electrical circuits for San Jose projects, what tends to trip up first-time ADU owners, and how the math changes between a studio JADU and a full two-bedroom detached ADU. For readers weighing the full project budget alongside the electrical scope, our breakdown of detached garage ADU conversion costs in San Jose covers where electrical work typically lands in the overall spend.
Contents
Figuring Out How Many Circuits a Garage ADU Actually Needs
Our team starts every project the same way: with a load calculation, not a guess. Garage ADU electrical circuits aren't a fixed number — they scale with square footage, appliance load, and whether the unit shares a panel with the main house or gets its own service.
Running the Load Calculation
California electrical code requires a documented load calculation before a permit gets issued, and our electricians run this early in design rather than waiting for plan check comments to force the issue. The calculation accounts for:
- General lighting and receptacle load, based on square footage
- Small-appliance circuits in the kitchen (minimum two, 20-amp each)
- Laundry circuit, if a washer/dryer hookup is part of the scope
- Fixed appliance loads — range, water heater, HVAC condenser, dryer
- A demand factor applied per NEC Article 220, which lets the total connected load be discounted somewhat since not everything runs at once
Most 400–600 square foot garage ADUs land around 60–100 amps of calculated demand once the demand factor is applied. That number, not square footage alone, is what determines whether a subpanel upgrade or a full service upgrade is on the table.
Checking Existing Panel Capacity
Before anyone talks circuit count, our team pulls the panel schedule on the main house. San Jose housing stock runs the gamut — some homes still have 100-amp services from the 1960s, others have been upgraded to 200 amps at some point. A quick capacity check tells us:
- How much spare amperage exists on the existing panel
- Whether open breaker slots are available, or a subpanel/tandem breaker is needed
- Whether the utility service itself needs an upgrade before any garage work starts
Pro tip from our crew: pulling the existing panel schedule before design finalizes almost always saves a change order later — panel capacity, not square footage, is usually the real ceiling on what a garage ADU can support.
Fast Ways to Right-Size the Panel and Circuit Count
A few decisions made early in design prevent expensive rework once framing and drywall are in. These are the moves our team leans on most often for garage ADU electrical circuits planning.
Sizing the Panel Before Design Gets Locked
- Confirm the load calculation before finalizing the kitchen and HVAC design — appliance selection changes the math
- Default to a 100-amp subpanel for anything with a full kitchen, rather than trying to squeeze by on 60 amps
- Leave two to four spare breaker slots in the subpanel for future additions — EV charging and heat pump upgrades are increasingly common add-ons
- Route conduit for the subpanel feed during the trenching phase, even if final wire size isn't locked yet
Mapping Dedicated Circuits Room by Room
Dedicated circuits are non-negotiable for specific loads. Our team maps these out room by room rather than treating the whole unit as one generic load:
- Kitchen: two small-appliance circuits, plus a dedicated circuit for the range/oven and one for the refrigerator
- Bathroom: one dedicated 20-amp GFCI circuit
- Laundry: dedicated 20-amp circuit for the washer, 30-amp (240V) for an electric dryer if applicable
- HVAC: dedicated circuit sized to the mini-split or condenser nameplate
- Water heater: dedicated circuit if electric or heat-pump style
- General living space: split across two or three 15/20-amp circuits depending on square footage
| Circuit | Typical Amperage | Protection Type |
|---|---|---|
| Kitchen small appliance (x2) | 20A | GFCI |
| Range/oven | 40–50A, 240V | Standard |
| Refrigerator | 15–20A | Dedicated |
| Bathroom | 20A | GFCI |
| Laundry (washer) | 20A | GFCI |
| Dryer | 30A, 240V | Standard |
| HVAC condenser/mini-split | 15–30A, 240V | Dedicated |
| Water heater (electric) | 30A, 240V | Dedicated |
| General living space (x2–3) | 15–20A | AFCI |
Subpanel vs. Main Panel Upgrade: Weighing the Options
Once the load calculation is done, the real decision point is how power gets to the garage: a new subpanel fed from the existing service, or a full main panel upgrade at the house. Both approaches show up constantly in our project files, and each comes with real trade-offs.
Subpanel Advantages and Trade-Offs
- Pro: Lower cost and shorter timeline — no utility coordination required in most cases
- Pro: Keeps the main house panel untouched, which avoids disruption to existing circuits
- Con: Only viable if the main service has enough spare capacity to support the added load
- Con: Trenching from the main panel to the garage adds excavation cost, especially on detached structures
Main Panel Upgrade Advantages and Trade-Offs
- Pro: Solves capacity constraints for the whole property, not just the ADU — useful if EV charging or solar is also planned
- Pro: Future-proofs the property against additional load from a second ADU or major appliance swap
- Con: Requires utility coordination and often a temporary power shutdown
- Con: Adds several thousand dollars and one to three weeks to the timeline in most San Jose projects
Our team typically recommends a subpanel first and only escalates to a full service upgrade when the load calculation clearly demands it. Jumping straight to a 200-amp main panel swap "just in case" rarely pencils out for a single garage ADU.
Electrical Mistakes That Delay San Jose ADU Permits
San Jose's plan check process catches electrical shortcuts fast, and rework after framing is far more expensive than getting the circuit count right on paper. These are the recurring issues our crews see.
Undersizing the Circuit Count Up Front
- Skipping the small-appliance circuit requirement in the kitchen — inspectors check for this specifically
- Running general living space and kitchen loads on shared circuits to save on breaker slots
- Failing to size HVAC circuits to the actual equipment nameplate, then discovering the mismatch at rough-in inspection
- Leaving zero spare capacity in the subpanel, which forces a redesign the moment a future owner wants an EV charger
Skipping Ahead of Plan Check
- Starting electrical rough-in before the load calculation is approved — this almost always results in a rip-out
- Assuming AFCI protection is optional in living spaces — San Jose enforces this per the current electrical code, no exceptions
- Forgetting GFCI protection in outdoor, garage-remnant, or wet-location circuits
- Not coordinating panel labeling and single-line diagrams with the plan set, which is one of the most common plan check correction items our team sees
Title 24 energy compliance also intersects with the electrical scope — high-efficacy lighting requirements and controls (occupancy sensors, dimming) get reviewed alongside the circuit plan, not separately. Our design and permitting team folds this into the same electrical drawing set to avoid a second review cycle.
Circuit Planning by ADU Type
Not every garage conversion needs the same electrical scope. Our team sizes garage ADU electrical circuits differently depending on whether the project is a compact JADU, a home office/studio, or a full detached in-law suite.
JADU and Studio Circuit Counts
- Junior ADUs sharing a kitchenette with the main house often need as few as six to eight dedicated circuits
- Home office and studio conversions without a full kitchen can often run on the existing garage sub-feed with minor upgrades
- Bathroom, general lighting, and one or two small-appliance circuits usually cover the bulk of a studio's needs
- These smaller scopes are frequently where a subpanel makes the most financial sense, since load demand stays modest
Full ADU and In-Law Suite Circuit Counts
- A full detached ADU with a complete kitchen, bathroom, laundry, and separate HVAC typically needs twelve to fourteen dedicated circuits
- In-law suites built for long-term occupancy often add a second bathroom circuit and higher-capacity HVAC, pushing the subpanel toward 100 amps
- Detached structures require trenched conduit runs, which our garage-to-ADU conversion teams coordinate with the plumbing and HVAC rough-in to avoid re-trenching the same yard twice
- Full ADUs intended for rental income benefit from a dedicated water heater circuit and separate metering consideration, even when full utility metering isn't required by the jurisdiction
Frequently Asked Questions
How many circuits does a typical garage ADU need in San Jose?
Most projects need between eight and fourteen dedicated circuits, depending on square footage and whether a full kitchen is included. Our team confirms the exact count through a load calculation early in design.
Does a garage ADU need its own electrical panel?
Not always. Many projects run on a subpanel fed from the existing house panel, as long as the main service has enough spare capacity. Larger or higher-load units sometimes require a full service upgrade instead.
Is a dedicated circuit required for the kitchen range?
Yes. Electric ranges and ovens require a dedicated 40–50 amp, 240-volt circuit under the current electrical code, separate from all other kitchen loads.
Are AFCI and GFCI protection both required in a garage ADU?
Yes, in most rooms. AFCI protection is required in general living spaces, and GFCI protection is required in kitchens, bathrooms, laundry areas, and any wet or garage-adjacent locations.
Does Title 24 affect the electrical circuit plan?
Indirectly, yes. Title 24 governs lighting efficacy and controls, which get reviewed alongside the electrical drawing set during San Jose's plan check process rather than as a separate submission.
How does electrical scope differ between a JADU and a full detached ADU?
A JADU sharing a kitchenette with the main house often needs only six to eight circuits, while a full detached ADU with a complete kitchen, laundry, and separate HVAC typically needs twelve to fourteen.
Key Takeaways
- Most San Jose garage ADUs need eight to fourteen dedicated circuits, and the exact count comes from a documented load calculation, not a square-footage guess.
- A subpanel is usually the faster, cheaper path when the main service has spare capacity, while a full panel upgrade makes sense when future loads like EV charging are in play.
- Kitchen, bathroom, laundry, and HVAC loads each require dedicated circuits with proper GFCI or AFCI protection to pass San Jose's plan check.
- Circuit scope shrinks significantly for JADUs and studios compared to full detached ADUs with complete kitchens and separate HVAC systems.
