ADU Electrical Panel Requirements and Costs in California

ADU Electrical: Getting the Power Right

Every Accessory Dwelling Unit needs a reliable, code-compliant electrical system. Whether you are building a new detached ADU, converting a detached garage, or creating a Junior ADU, the electrical panel and wiring infrastructure are among the most important systems in the project.

The electrical panel is the heart of your ADU's power distribution system. It receives electricity from the utility service and distributes it through individual circuits to every outlet, light, appliance, and system in the unit. Getting the panel size, configuration, and installation right is essential for safety, code compliance, and the long-term functionality of your ADU.

This guide covers everything California homeowners need to know about ADU electrical panel requirements, including how to determine the right panel size, the difference between a subpanel and a new service, typical costs, Title 24 energy code compliance, and tips for working effectively with your electrician.

Subpanel vs. New Service: Which Does Your ADU Need?

The first major decision in your ADU electrical planning is whether to install a subpanel fed from your existing main house panel or to establish a completely new electrical service for the ADU. Each option has distinct advantages, cost implications, and situations where it makes the most sense.

Option 1: Subpanel Fed from Existing Main Panel

A subpanel is a secondary electrical panel that receives its power from the main house panel through a dedicated feeder circuit. The subpanel then distributes power to the ADU's individual circuits.

When this works:

• Your existing main panel has adequate capacity (typically 200 amps or more)
• The ADU's electrical load is 60 to 100 amps
• The distance between the main panel and ADU is reasonable (under 100 feet)
• Your utility provider allows subpanel connections for ADUs

Typical cost: $2,500 to $6,000 for the subpanel, feeder circuit, and installation.

Option 2: New Electrical Service (Separate Meter)

A new electrical service means a completely independent connection from the utility to the ADU, with its own meter, main disconnect, and panel. This is essentially treating the ADU as a separate building from an electrical standpoint.

When this is required or recommended:

• Your existing main panel cannot support the additional ADU load
• The ADU has high electrical demands (electric cooking, electric water heater, EV charging)
• The distance between the main panel and ADU exceeds 100 feet
• Your utility provider requires a separate meter
• You want separate utility billing for rental purposes

Typical cost: $5,000 to $15,000 for the new service, including meter installation, panel, and utility coordination.

Factor	Subpanel	New Service
Typical cost	$2,500 - $6,000	$5,000 - $15,000
Separate meter	No (shared with main house)	Yes
Separate billing	Not directly (sub-meter possible)	Yes
Main panel capacity needed	Must have spare capacity	Independent
Installation timeline	1-2 days	2-6 weeks (utility coordination)
Best for	Budget projects, garage conversions	Rental ADUs, high-demand units

How to Size Your ADU Electrical Panel

Proper panel sizing ensures your ADU has enough electrical capacity for all current and future needs. An undersized panel will trip breakers frequently and may not pass inspection, while an oversized panel wastes money on unnecessary capacity.

Load Calculation Method

Your electrician will perform a load calculation per the National Electrical Code (NEC) Article 220 to determine the required panel size. Here is a simplified version of how this calculation works for a typical ADU:

Load Type	Typical Wattage	Notes
General lighting and receptacles	3 watts per sq ft	600 sq ft ADU = 1,800W
Small appliance circuits (2 required)	1,500W each	3,000W total
Laundry circuit	1,500W	Required if laundry hookup provided
Electric range	8,000 - 12,000W	240V circuit
Electric water heater	4,500W	240V circuit
HVAC (mini-split)	2,000 - 4,000W	240V circuit for most units
Washer/dryer	5,000 - 6,000W	Electric dryer on 240V
EV charger (optional)	7,200W (Level 2)	240V, 40A circuit

Common Panel Sizes for ADUs

60-amp panel: Suitable for small ADUs and JADUs with gas cooking, gas water heating, and minimal electrical loads. This is the minimum size that most jurisdictions will accept.

100-amp panel: The most common choice for standard ADUs with all-electric systems. Provides enough capacity for electric cooking, electric water heating, mini-split HVAC, and general household loads.

125-amp or 200-amp panel: Required for ADUs with high electrical demands, such as those with EV charging, electric dryers, and multiple high-draw appliances.

For most California ADUs built in 2026, a 100-amp panel is the recommended starting point. California's electrification requirements and Title 24 energy standards increasingly favor all-electric systems, which require more electrical capacity than gas-assisted designs.

Required Circuits for Your ADU

California building code and the NEC specify minimum circuit requirements for dwelling units. Here is a breakdown of the circuits your ADU will need:

Required Circuits

• General lighting circuits: At least one 15-amp or 20-amp circuit for every 600 square feet of living space
• Kitchen small appliance circuits: Minimum of two 20-amp circuits dedicated to kitchen countertop outlets
• Bathroom circuit: One 20-amp GFCI-protected circuit dedicated to the bathroom
• Laundry circuit: One 20-amp circuit dedicated to the laundry area (if washer/dryer hookups are provided)
• Refrigerator circuit: One dedicated 20-amp circuit (recommended but not always code-required)
• Dishwasher circuit: One dedicated 20-amp circuit
• Garbage disposal circuit: Can share with dishwasher or have its own 20-amp circuit
• Range/cooktop circuit: 40-amp or 50-amp 240V circuit for electric range
• HVAC circuit: Dedicated circuit per manufacturer requirements (typically 20-amp or 30-amp 240V)
• Water heater circuit: 30-amp 240V circuit for electric water heater

GFCI and AFCI Protection

California follows the 2023 NEC, which requires extensive GFCI and AFCI protection throughout dwelling units:

• GFCI protection required: All kitchen outlets, bathroom outlets, laundry area outlets, outdoor outlets, and any outlets within 6 feet of a water source
• AFCI protection required: All 15-amp and 20-amp branch circuits in living areas, bedrooms, hallways, closets, and similar spaces

AFCI breakers cost more than standard breakers ($30 to $50 each vs. $5 to $10), so this requirement adds to the overall panel and circuit cost. However, AFCI protection significantly reduces the risk of electrical fires caused by arc faults in wiring.

Title 24 Electrical Requirements

California's Title 24 energy code has specific requirements for electrical systems in new construction, including ADUs. Key requirements that affect your ADU electrical design include:

Solar Ready

New ADUs must be "solar ready," meaning the electrical system must include provisions for future solar panel installation. This includes a reserved space on the electrical panel for solar circuit breakers and conduit from the panel to the roof area. The actual installation of solar panels is not required, but the infrastructure must be in place.

EV Ready

Under California's CALGreen code, new ADUs must include at least one EV-ready parking space with a 240V, 40-amp circuit run to the parking area. This requirement adds $500 to $1,500 to the electrical scope but ensures the ADU is ready for electric vehicle charging.

Energy-Efficient Lighting

All lighting in new California ADUs must be high-efficacy (LED or equivalent). Recessed can lights must be airtight rated (IC-AT) to prevent air leakage through the ceiling. Dimming capability is required in specific locations, including the kitchen, living room, and bedroom.

Complete ADU Electrical Cost Breakdown

Electrical Component	Cost Range
Subpanel (60-100 amp)	$1,200 - $3,000
Feeder circuit to ADU	$1,000 - $4,000
Main panel upgrade (if needed)	$2,000 - $4,500
Rough-in wiring (all circuits)	$3,000 - $8,000
Fixtures and devices	$1,000 - $3,000
EV ready circuit	$500 - $1,500
Solar ready provisions	$300 - $800
Smoke/CO detectors (hardwired)	$200 - $500
Total electrical budget	$5,000 - $15,000

For a new electrical service with a separate meter, add $3,000 to $8,000 for the utility connection, meter base, and coordination with the electric company. This brings the total electrical budget for a separately metered ADU to $8,000 to $23,000.

Frequently Asked Questions About ADU Electrical

Can my ADU share the main house electrical panel?

Yes, if your existing main panel has adequate spare capacity. Most 200-amp main panels can support a 60 to 100-amp subpanel for the ADU. Your electrician will perform a load calculation on the existing panel to determine if it can support the additional ADU load. If the main panel is only 100 or 150 amps, you may need to upgrade it before adding the ADU subpanel.

Do I need a separate electrical meter for my ADU?

California state law does not require a separate meter for ADUs. However, some homeowners choose to install one for accurate tenant billing. Your utility provider (such as LADWP or SCE) may have specific requirements. A separate meter adds $3,000 to $8,000 to the project but simplifies tenant billing and allows the ADU to have its own utility account.

How much does it cost to upgrade my main panel to 200 amps?

Upgrading your main panel from 100 or 150 amps to 200 amps typically costs $2,000 to $4,500, including the new panel, breakers, utility coordination, and permit. This upgrade is often necessary when adding an ADU subpanel to an older home with a smaller main panel.

What size wire do I need for the ADU subpanel feeder?

The wire size depends on the amperage of the subpanel and the distance from the main panel. For a 100-amp subpanel within 50 feet of the main panel, #2 AWG copper or 1/0 AWG aluminum wire is typically required. For longer runs, larger wire sizes may be needed to account for voltage drop. Your electrician will calculate the exact wire size based on your specific installation.

Are solar panels required on my ADU?

Solar panels are not required on the ADU itself, but the ADU must be "solar ready," meaning the electrical infrastructure must support future solar installation. This includes reserved breaker space in the panel and conduit from the panel to the roof area. If the main house already has solar panels, the system may need to be expanded to offset the ADU's energy consumption, depending on local requirements.

What happens if my ADU electrical system fails inspection?

Common reasons for failed electrical inspections include missing GFCI protection, incorrect wire sizing, improper grounding, and missing AFCI breakers. Your electrician will make the necessary corrections and schedule a re-inspection. Re-inspection fees are typically $50 to $150. Working with an experienced electrician who is familiar with current code requirements minimizes the risk of failed inspections.

Electrical Panel Sizing Guide for California ADUs

Choosing the right panel size for your ADU is critical. An undersized panel limits what you can power, while an oversized panel wastes money. Here is a practical guide to help you determine the right electrical panel size for your ADU project.

ADU Size	Recommended Panel Size	Typical Usage	Estimated Panel Cost
Studio / JADU (under 500 sq ft)	60 to 100 amps	Basic lighting, outlets, small appliances, mini-split HVAC	$1,200 to $2,500
One-Bedroom (500 to 750 sq ft)	100 to 125 amps	Full kitchen, washer/dryer, central HVAC, water heater	$2,000 to $3,500
Two-Bedroom (750 to 1,200 sq ft)	125 to 200 amps	Multiple circuits, EV charger ready, full appliance package	$2,500 to $4,500

When calculating your panel size, account for all major electrical loads including HVAC systems, kitchen appliances, water heaters, and any planned future additions like EV chargers or hot tubs. California's Title 24 energy code may also require specific provisions for solar readiness and energy storage, which affect your panel sizing decisions.

Smart Home Wiring Considerations for Your ADU

Modern ADUs benefit greatly from smart home wiring, and planning for it during construction is far less expensive than retrofitting later. Here are the key smart home wiring considerations California homeowners should address during the electrical planning phase.

• Run Cat6 Ethernet cable to every room. Even with strong Wi-Fi, hardwired connections provide faster and more reliable internet for streaming, video calls, and smart home hubs. Install at least one Ethernet drop per room plus additional drops near your entertainment center and home office area.
• Install smart switch wiring. Many smart switches require a neutral wire in the switch box. Make sure your electrician runs neutral wires to every switch location, as older wiring practices sometimes skip this step.
• Pre-wire for security cameras. Run conduit or low-voltage wiring to exterior locations where you might want security cameras. Include at least two to four camera positions around your ADU for complete coverage.
• Plan for a smart home hub location. Designate a central closet or cabinet area with power, Ethernet, and ventilation for your networking equipment and smart home hub. This keeps equipment organized and accessible.
• Include USB outlets in key locations. Install combination outlets with built-in USB-A and USB-C ports in the kitchen, bedroom, and living area. These eliminate the need for bulky charging adapters.
• Wire for smart thermostats. Most smart thermostats require a C-wire (common wire) for power. Have your HVAC installer and electrician coordinate to ensure proper wiring to your thermostat location.

Investing in smart home wiring during construction typically adds $1,500 to $4,000 to your electrical budget but can significantly increase your ADU's rental value and appeal to tenants who expect modern connectivity.

Frequently Asked Questions About ADU Electrical Panels in California

Can my existing main panel support a new ADU?

It depends on your current panel's capacity and how much of it is already in use. Many older California homes have 100-amp or 150-amp main panels that may not have enough spare capacity for an ADU. Your electrician will perform a load calculation to determine if your existing panel can support the additional circuits. If not, you may need to upgrade your main panel to 200 amps or install a separate meter and panel for the ADU. California law now allows ADUs to share the existing electrical service without requiring a main panel upgrade in many situations.

How much does it cost to run electrical service to a detached ADU?

Running electrical service from your main house to a detached ADU typically costs $3,000 to $12,000 depending on the distance, whether you trench underground or run overhead, and the amperage of the service. Underground runs are more expensive but required in most California jurisdictions for new construction. Factor in the cost of trenching, conduit, wire, a new subpanel, and the electrician's labor. Longer distances and larger wire sizes increase costs proportionally.

Does California require solar panels on new ADUs?

California's Title 24 energy code requires solar readiness for most new ADUs, but the actual solar panel requirement depends on the ADU's size and type. ADUs under 750 square feet are generally exempt from the solar mandate, but your electrical panel must still be solar-ready with adequate space for future solar circuit breakers. ADUs over 750 square feet may need to comply with the full solar requirement. Check with your local building department for the specific requirements that apply to your project.

What is the difference between a subpanel and a separate meter for an ADU?

A subpanel connects to your main house's electrical panel and shares the same utility meter, meaning all electricity usage appears on one bill. A separate meter gives the ADU its own utility account, allowing tenants to pay their own electricity bills. Separate meters cost more to install ($2,000 to $5,000 more) but are highly recommended for rental ADUs because they simplify billing and eliminate disputes over utility costs. Your local utility company will need to approve and install the separate meter.