Accessory dwelling unit (ADU) electrical requirements in California tie together panel sizing, sub panels, load calculations, Title 24 energy code, and in many cases separate metering. Getting that package right is what keeps your project safe, code compliant, and ready for the next decade of electrification.
You may also hear ADUs described today as “all-electric.” While gas appliances are still permitted in many jurisdictions, most new ADUs are being designed with electric space conditioning, cooking, and heat pump water heating. This shift is driven less by prohibition and more by practical factors like energy code compliance, utility coordination, and the added cost of extending new gas service to a detached unit.
With so many more backyard homes coming online, inspectors, utilities, and local jurisdictions are applying electrical rules more consistently and with more scrutiny. This guide walks through what those requirements actually look like for a homeowner. We will cover the big picture rules statewide, how they get interpreted in San Diego, and where panel upgrades and separate meters come into play. Then we will show how Snap ADU handles electrical design, permitting, and utility coordination so you are not stuck translating technical bulletins on your own.
Note that these requirements will vary for each jurisdiction and utility authority, but this article focuses on San Diego Gas & Electric (SDGE). SDGE provides natural gas and electricity to San Diego County and southern Orange County in southwestern California.
- Quick Start: ADU Electrical Requirements in California
- Why Many New ADUs Are Designed All-Electric
- Understanding Load Calculations for ADUs
- Electric Panels for ADUs in San Diego
- Electrical Service Upgrade for an ADU: When is it required?
- Existing power source: Underground vs. overhead power lines?
- What is the process with SDGE for your ADU work order?
- Cable & Internet Service for Your ADU
- ADU electrical checklist for California homeowners
- Descriptions on Electrical Drawings for ADUs
- Reach out to experts for your unique situation
Quick Start: ADU Electrical Requirements in California
If you only read one section, make it this one. These are the headline requirements that drive most electrical scopes on new ADUs in California:
Load calculation
A licensed electrician must perform a formal load calculation that adds up all appliances and circuits, converts wattage to amps, and confirms that both the main service and any subpanels can handle the peak demand without nuisance tripping or overheating.
Panel capacity
Most ADUs end up with 100 to 200 amps of capacity allocated, often via a 125 amp subpanel, to support HVAC, kitchen, laundry, and future loads such as EV charging.
Title 24 & Solar Requirements
Many new detached ADUs must include a solar PV system sized according to state formulas, and all new single family homes that include an ADU must meet energy storage system ready requirements (e.g. identifying four backed up circuits and ensuring panel equipment can support 60 amps of backup capacity).
Read more about Title 24 requirements. Read more about ADU solar requirements.
Metering & Utility Coordination
Utility providers increasingly push new ADUs toward separate metering, which changes panel layout, trenching, and project costs. In SDG&E territory, new ADUs typically involve a Builder Services application, review of panel locations, and often service upgrades.
The same consideration can apply to gas service. If a project includes gas appliances, the utility may require a new gas meter for the ADU, which introduces additional application timelines and installation costs. Designing the ADU as all-electric can eliminate that step entirely, reducing coordination with the utility and simplifying the construction schedule.
Local Code Details
Requirements for outlet spacing, GFCI and AFCI protection, and high efficacy lighting come from the National Electrical Code as adopted by California, then interpreted by your city or county. Each city handles electrical requirements differently as far as their processing sequence. For example, San Diego requires you to obtain a right-of-way permit for any electrical work to be performed before it will issue the building permit for the ADU. This means proper planning is crucial to avoid months of delays.
It is important to note that fuel-type rules are evolving. Court decisions and policy changes have shifted how some cities regulate natural gas, so requirements can change over time. Most jurisdictions today allow either fuel source, but energy standards and utility logistics often make electric systems the more straightforward option for ADUs.
The rest of the page breaks these points down and shows how electrical requirements affect real ADU projects in San Diego County.
Why Many New ADUs Are Designed All-Electric
Recent updates to California’s energy standards (Title 24) increasingly favor high efficiency electric systems such as heat pump HVAC and heat pump water heaters. While these standards don’t universally ban gas appliances, they make mixed fuel designs harder to model for compliance in some climate zones.
In addition, adding gas to a new ADU often requires a separate gas meter, new utility coordination, and trenching—costs that can outweigh the price difference between gas and electric equipment. Because of this, many design teams and builders now default to all-electric layouts as the simplest path through permitting, energy modeling, and construction.
For example, on recent projects we have confirmed that electric heat pump tank water heaters meet energy code requirements while avoiding the need to extend new gas infrastructure.
Understanding Load Calculations for ADUs
Early in the ADU planning process, it’s essential to perform electrical load calculations for both the main house and the ADU. San Diego Gas & Electric (SDGE) requires load calculations for the entire property, even if there are separate meters. This ensures that the proper size wire and amount of amperage are supplied to the property, which is then distributed to individual units. The power is separated once on the property, not before it arrives. This is why evaluating the existing panel and determining if an upgrade is needed is relevant and necessary. These calculations help ensure that the combined electrical demand of the main house and ADU can be adequately supported, avoiding potential issues with power supply and safety.
All-electric ADUs place more demand on the electrical service up front, which is why accurate load calculations are especially important when systems like heat pump HVAC, electric dryers, and induction ranges are included.
As part of our Feasibility Study, SnapADU evaluates the load calculations for your property with the addition of the ADU.
How many amps does an ADU require?
A standard accessory dwelling unit will draw approximately 80-100 amps of power. For our ADUs, which are typically all-electric, we generally install a 125-amp sub-panel. This provides a little extra room, accounting for any future electrical demands that might arise. Moreover, this allows us to de-rate 25 amps specifically for solar accommodations.
Our standard specification includes an electric heat pump water heater, typically located within the ADU laundry area. These systems are highly efficient, meet current energy code expectations, and avoid the need for combustion venting or extending gas piping to the unit.
What about an electrical vehicle (EV) charger?
Our scope of work includes preparation for a future EV charger if the client wishes to install one. This is the minimum requirement of the CEC. We will provide a conduit from the sub panel on the ADU to the location of the future EV charger and cover this with a termination box or blank cover plate. If the client wishes for us to install a 240V plug and wire back to the sub panel, this will be an additional $800-$1,200 depending on the distance from the panel.
Electric Panels for ADUs in San Diego
An ADU typically requires a separate electrical panel, which is typically located on the primary residence adjacent to the meter serving the primary unit (not on the ADU itself). This is because SDGE requires that all meters serving a property be grouped together when possible.
From this separately metered panel, a sub-feed is run to a sub-panel located on the exterior wall of the ADU. In cases where the ADU is situated more than 150′ from the primary residence, a separate meter panel may be installed directly on the ADU itself. Additionally, a separate service line from the electrical main will need to be run to the ADU.
In the early years of ADU adoption, there was inconsistent enforcement of separate metering, meaning some ADUs were allowed to be connected to the existing meter on the primary residence. As of March 2023, SDG&E has confirmed that all new accessory dwelling unit construction requires a separate electric meter.
However, if the existing electrical service and panel size that exists on the property can accommodate the additional load from the proposed ADU, SDGE is unable to enforce this requirement. It is then up to the discretion of the homeowner whether a separate meter is installed.
How much does a separate electrical meter for the ADU cost?
Installing a separate electrical meter for your ADU typically costs around $15,000. This cost includes coordination with SDGE and local building officials, trenching and installation by an electrician, providing and installing separate electrical meters, and patching stucco or siding on the main home as needed. If your existing main electrical panel can’t accommodate an additional meter, it will need to be replaced with a new multi-meter main service panel.
Additional considerations such as upgrading the existing weather-head, installing underground conduit, relocating the main service panel, and work in the public right of way are not included in the base cost. Additional costs may arise if SDGE adds requirements after their representative evaluates the site, which can take 2-4 months.
Clearance & Separation Requirements for Electrical Panels
SDG&E requires a clear, unobstructed wall area behind the electrical panel. According to their guidelines, the wall area behind the meter panel must be free of obstructions, including water pipes, hose bibs, sewer cleanouts, drain spouts, electrical conduits, and similar items. A minimum clearance of 36 inches of level working space is required in front of the electrical meters for safe access and maintenance. See diagram below, taken from page 230 of the current set of SDGE guidelines.
These clearances are something a utility specialist should evaluate early in the ADU process so that all necessary planning can take place in plenty of time. Conflicts with meter locations are common, and it’s important to plan ahead.
What if I don’t install a separate meter on the ADU? Will anyone notice?
We recently heard from a homeowner who did not install a separate meter on her new ADU. A few months later, she had to have SDGE visit her property about a different matter on her main house. When they investigated, they also called out that she had not installed a separate meter for her ADU and would be required to do so.
In many cases, an ADU project will require both a separate meter for the ADU and an upgrade to the service size. The scope of work involved to accomplish both of these upgrades involves many of the same processes as far as required skills & labor (e.g. removing existing panel and replacing with a new one). The only thing that is different when increasing the service size is that the new panel will be larger than the existing one that was removed.
When you already have an existing 400A single meter panel, you will still need to replace the panel with a 400A dual meter panel.
Electrical Service Upgrade for an ADU: When is it required?
The required size of your electric service for the property is determined by several components, including the main service panel, service size, and service conduit. We’ll explain what these terms mean and how they relate to a potential upgrade to your electric service. We’ll also discuss the circumstances under which you may need to upgrade your electric service and the steps involved in doing so.
First, let’s establish terminology:
- Main Service Panel (MSP) – The primary panel, typically located on the PDU, which houses the meter bubble and accepts the SDGE service. Service panels come in 100A, 125A, 150A, 200A, 225A, and 400A.
- Service Size – The amperage being brought to the MSP by SDGE. This service drop is typically 100A, 200A, or 400A.
- Service Conduit – The conduit which houses the underground service wire. This conduit connects the MSP to the SDGE transformer, handhole, or vault at the street.
All of these components are proportional to the service size:
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- 100A service size means 100A MSP and 2” conduit.
- 200A service size means 200A MSP and 3” conduit.
- 400A service size means 400A MSP and 3” conduit.
Situations that apply when upgrading service
- When upgrading from 100A to 200A and service is 2” underground conduit, it is likely that it will require an upgrade to 3” conduit. SDGE will always need to field the site to determine if a conduit upsize is needed.
- When upgrading to 400A, the conduit will typically need to be upgraded because 400A requires 3” conduit. Unless the existing service is 200A and it was installed after 2015, in which case the conduit may already be 3”.
If the existing service size needs to be upgraded and the service is underground from the main panel to the connection point at the street, one of several outcomes will happen:
- Existing conduit size is adequate for the new upgraded service and we do not need to touch anything but the panel.
- Existing conduit is undersized for the new upgraded service and we need to replace the conduit from MSP (main service panel on PDU) to an SDGE handhole/transformer/vault that exists:
- in an easement on the client’s property. In this case, there is no work that needs to be performed in the right of way (ROW).
- across or down the street from the client’s property. In this case, ROW work will be required to install a new upsized conduit to said handhole/transformer.
Other unusual scenarios with conduit upgrades
There’s also important context to note on conduit upgrade requirements. Sometimes the underground service is not in conduit at all and is SIDA, DBC cable – “direct-burial cable.” Because the DBC cable is stubbed up into the panel with a 90deg conduit sweep through the foundation and into the wall, we cannot tell the difference between SIDA and conduit. This information can only be obtained through an SDGE service order request. If the underground wire is determined to be DBC by SDGE, any change/upgrade to the MSP will trigger a conduit upgrade.
All of this information is what SnapADU has gathered from recent service upgrades. These rules are always changing. While there is an SDGE Service Standards & Guide, many of the requirements and the parameters are largely set by the planner assigned to the project, so each case will be different. This is yet another reason it is so crucial to work with an experienced contractor on your ADU build so your team can find workable solutions – and advocate for you – in these complex scenarios.
Why should your ADU contractor upgrade your existing main electrical panel?
An upgrade to your existing Main Service Panel can occur for a variety of reasons. This includes undersized, unsafe, too few breaker slots, or need for a solar-ready panel. Whatever the cause it is best to have your ADU contractor manage the scope of work for several reasons.
- Coordination with the utility provider which has long, long lead times, typically 6 months at a minimum. We initiate a work order for every project as soon as a sales proposal is signed and begin coordination with them so that there is no delay caused by the long lead time.
- The utility provider does not allow duplicate service orders on the same property. Since the ADU contractor immediately requests a work order, any other provider would not be able to do so.
- Every ADU requires its own, stand-alone Sub Electrical Panel (“sub-panel” for short) which needs to be of the correct capacity and model to accept the electrical circuits from the ADU as well to connect to the Main Service Panel.
While it can take six months or more to complete the work from application to re-energization, the physical work onsite typically take only two days, for which power is out for only several hours on average. Costs for an upgrade will range widely depending upon the reason for the upgrade and proximity to the High Power Transmission Lines.
Existing power source: Underground vs. overhead power lines?
Before starting the construction of an ADU, it’s crucial to assess the existing power source & type for two reasons:
- Determining the best location for the ADU should factor in any potential interference with the existing power source, which will have to either be avoided or be rerouted.
- Upgrading the electrical service (if necessary) will vary in complexity & cost based on the type of power line.
There are two ways that power can service your property: underground power lines or overhead power lines.
Underground lines
One of the most common issues that can arise is the presence of underground power lines running through the area where the ADU is planned to be built. In such cases, it’s essential to map out the location of the underground power lines early on in the feasibility process to either avoid or plan a move if needed.
Overhead lines
Overhead electrical service drops that intersect the proposed ADU, or do not meet clearance requirements need to be relocated. This typically costs between $2,000 and $3,000 if no work to the existing service panel is needed.
In some cases, the new overhead connection for the electrical service drop must be located on the proposed ADU. In such instances, temporary power must be established on the property in order to supply power to the primary residence until the new permanent service connection can be made on the newly constructed ADU. This adds an additional $4-5K for temporary power to the main home.
The presence of these lines can make it challenging to move large equipment and materials, which can delay the construction process. To avoid this issue, it’s important to identify the location of the overhead lines and plan the construction around them.
Also note their are some nuances in each jurisdiction with overhead lines. In Encinitas, overhead service greater than 200 amps needs to be undergrounded from the nearest pole, for all structures greater than 500 sqft.
SDGE outlines clearances over buildings & structures that must be maintained. Notably, we would be looking at the “service drop,” meaning just the one wire from the power pole to the primary dwelling. See the image below specifying the 8′ minimum vertical clearance requirement from a structure.
High voltage power lines
High voltage power lines are typically carried on tall metal towers or wooden poles that are erected along a path known as a right-of-way (ROW) or easement. In the context of high voltage power lines, an easement grants the utility company the right to install and maintain power lines, transformers, and other equipment on the property owner’s land. You can never encroach on a utility easement; building a structure too close to the power lines can interfere with the proper functioning of the lines or pose a safety risk.
As you may have guessed by the depth of content in our blog articles, we work on ADU electrical and utility issues every single day and continue to build out our understanding of the triggers for additional work, when to push back, and how to advise our clients to best proceed. If you’d like to talk about your project, reach out to schedule a free discovery call.
What is the process with SDGE for your ADU work order?
SDGE will need to be involved in processing the work order for a utility upgrade. This timeline begins when all of the requested documentation is submitted to the SDGE service order request team. This point is called “AFS” = Applicant Final Submittal.
From SDGE as of 2025, below are the Current Project Request Timelines (once the AFS date is acquired).
Current SDGE Project Request Timelines
Service Orders (approximately 8-10 weeks) A service order is when there is a nearby source to meet your energy needs.
Work Orders (approximately 26-30 weeks) A work order is applicable when there is no viable source creating the requested fuels to meet your projects needs. Further process explained below on how this breaks down:
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- Preliminary Design (18-20 weeks): This is when the backbone of the work and research is done. The design team is creating distribution that meets the needs of your project. Once the preliminary design is completed it will be published to you for review and signatures.
- Final Design (6-8 weeks): During this time frame the Planning Team is reviewing the project and applying the allowances is applicable
Start your SDGE Work Early
It’s imperative to begin the SDGE process as early as possible in your ADU project planning. Delays in utility upgrades can significantly impact your ADU timeline, so understanding and initiating this process at the outset can help mitigate potential setbacks. By aligning with SDGE’s timelines and requirements from the start, you can ensure a smoother progression of your ADU construction, avoiding unnecessary delays and ensuring your project stays on track.
Also be aware of nuances with things like your ADU address. SDGE will require your ADU address information to initiate service.
See the handout SDGE – Builder Services Additional Dwelling Unit (ADU) Checklist
Cable & Internet Service for Your ADU
While most of our blog focuses on electrical panels and utility meters, another common question is how to get cable or internet service to the ADU. Homeowners are often surprised when providers like Cox or Spectrum initially flag an ADU as “unserviceable,” even if the main house already has service.
Pro tip: Confirm with your ADU builder or electrician that a conduit is in place, accessible, and has a pull string before scheduling the cable company. This small step can save weeks of back-and-forth, so plan the infrastructure correctly from the start.
Here’s how it typically works:
Conduit to the panel
During construction, we run a conduit from the ADU back to the Primary Dwelling Unit (PDU), where the main service panels are mounted on the exterior wall. Cable companies are expected to connect their line to the PDU (either overhead or underground) and then transition into the conduit we’ve stubbed near the electrical meter panels.
Pull string required
One of the biggest hang-ups is that Cox techs often arrive without a way to fish cable through long conduit runs. If there isn’t a pull string already in place, they may declare the property “unserviceable.” To avoid this, we recommend ensuring the conduit has a pull string before the service call. Some installers use a “mouse and vacuum” trick to pull the string—yes, literally sucking a string through the conduit with a shop vac.
Service location
In most cases, the cable provider does not need to go inside the main house to establish service for the ADU. They will connect at the exterior PDU and then pull cable through the conduit. Getting cable to your ADU is usually straightforward once the conduit and pull string are set. The rest is persistence (and sometimes patience) with your provider’s field techs.
ADU electrical checklist for California homeowners
Before you submit for permits, you should be able to answer all of the following:
- Panel and meter strategy
- What is the existing main service size for the property?
- Will the ADU use a new subpanel, or will you upgrade the main panel with a dual meter and feed the ADU from there?
- Load calculation
- Has a licensed electrician completed a written load calculation that accounts for HVAC, water heating, kitchen, laundry, EV charging, and general lighting and receptacles?
- Have you “value engineered” the ADU design based on the load calculation? In other words, if the calculation is close, could you remove 1-2 elements from the ADU or main home to avoid the upgrade requirements and keep your existing panel?
- Title 24 and solar
- Does your ADU trigger solar requirements, and if so, what system size is being used in the energy model? Did you check for solar exemption under 1.8 kw?
- Has your design identified the four or more branch circuits that will be ESS ready for a future battery?
- Site and utility coordination
- Have you confirmed clearances to overhead lines, transformers, and gas risers per SDG&E standards?
- Does your site plan clearly show panel, meter, and trench locations for SDG&E review?
- Code details inside the ADU
- Are GFCI and AFCI devices specified correctly for kitchens, baths, bedrooms, and exterior outlets?
- Does your plan meet high efficacy lighting requirements and control locations under Title 24?
If any of these boxes are unclear, that is where your design build team should step in. Homeowners should not have to interpret panel busbar ratings, ESS fact sheets, or utility handbooks on their own.
Descriptions on Electrical Drawings for ADUs
You may see the following descriptions on your electrical drawings for your accessory dwelling unit:
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- Sub panel – The main electrical panel dedicated to your ADU, distributing electricity to various circuits within the unit. This panel is separate from the primary residence’s electrical system, allowing for independent control and functionality.
- Solar – Connections for the ADU’s solar power system. This includes wiring and components that integrate solar panels with your electrical system, helping offset energy costs and supporting renewable energy use.
- ESS panel and j-box for ESS – The ESS (Energy Storage System) panel and junction box are designed for integrating a future battery storage system. The ESS panel manages the storage and distribution of solar or backup power, while the junction box facilitates safe and organized wiring connections.
- LV Can – Short for Low Voltage Can (or known as a low voltage box), this is a central hub for low-voltage connections such as internet, TV, and smart home devices. It provides an organized location for running wires and managing low-voltage systems within the ADU.
- Data – Refers to COAX (coaxial cable) connections used for delivering cable TV or internet services. Coaxial cables are primarily used by service providers for high-speed data and television signals.
- TV – Denotes the outlet and brush plate box used to conceal and organize the cables connecting a television to power and data sources. This creates a clean and tidy appearance for wall-mounted TVs. While both “Data” and “TV” deal with connectivity, Data (COAX) refers to the physical cable that delivers internet and TV signals from a service provider to a modem, router, or device. On the other hand, TV refers specifically to the outlet and connection point where a television plugs into power and receives its signal, which may include HDMI, COAX, or other connection types, depending on the setup.
- RJ45 – Refers to Ethernet connections used for wired internet networking. RJ45 cables are essential for high-speed, reliable internet connections in your ADU and can support streaming, gaming, and other data-intensive activities.
Reach out to experts for your unique situation
All information included in this blog is based on our past design/permit/build experiences and our best understanding of local and state regulations as of this time. It may be the case that the regulations in your area differ from those stated here, or that local interpretation will vary. With our clients, we do our best to identify the most likely scenarios and interpretations so that we can accurately advise on budget and scope. In the end, we don’t want anyone to be surprised… at least not by the costs or process (though it’s a good thing to be surprised by how smoothly things go and how great the ADU looks after it’s completed!).
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