ADU Electrical Requirements in San Diego, CA

ADU electrical requirements in San Diego catch more homeowners off guard than any other part of the backyard-unit process. The framing, the roofline, the finishes — those are the parts everyone plans for. What usually gets discovered late, sometimes after the walls are already up, is that the existing electrical panel cannot legally or safely support a new unit without changes that go well beyond running a few extra wires.

San Diego has one of the highest concentrations of ADU permit activity in the state, and the electrical scope is where a large share of those projects stall in plan check. Getting the panel, the meter, and the load calculation right the first time is the difference between a smooth build and months of back-and-forth with San Diego Gas & Electric (SDG&E) and the city’s Development Services Department.

Does an ADU Need Its Own Electrical Panel?

Not always — but more often than homeowners expect. A common assumption is that an ADU can simply tap into the main house’s existing panel the same way a new bedroom addition would. Sometimes that’s true, especially for a small junior ADU (JADU) built inside the existing footprint of the home, where the added load is modest and the main panel already has spare capacity. For a detached ADU, though, the added load from HVAC, a kitchen, a water heater, laundry, and general household use is usually enough to push the property past what the existing service can support.

Whether the ADU needs a dedicated subpanel, an entirely separate service, or can share the existing panel comes down to one thing: the load calculation. Skipping that step and guessing at panel size is one of the most common — and most expensive — mistakes in ADU planning.

JADU vs. Detached ADU: Why the Electrical Scope Is So Different

A junior ADU converted from existing space inside a single-family home — a garage conversion or a converted bonus room, for example — typically draws from the main house’s existing panel with only minor additions, since the JADU shares walls, plumbing runs, and often a kitchenette rather than a full kitchen. A detached, full-size ADU is a different project entirely from an electrical standpoint. It’s effectively a second small house on the same lot, which means it needs its own complete circuit layout: dedicated circuits for the kitchen, laundry, HVAC, and general lighting and receptacles, sized and permitted the same way a standalone home would be.

This distinction matters most when homeowners are comparing cost estimates. A JADU electrical scope and a detached ADU electrical scope can differ by thousands of dollars, and comparing a quote for one against a quote for the other leads to a lot of confusion during the bidding process.

SDG&E’s Separate Meter Rule for New ADUs

This is the part that surprises the most people. SDG&E’s Service Standards and Guide sets a firm cap: a new dwelling unit meter combined with the existing meter cannot exceed 225 amps maximum on a single-phase, 120/240-volt residential service. In practical terms, that limits how much can be added to a shared service before a separate connection becomes necessary.

SDG&E’s guidance for new construction, which explicitly covers ADUs, duplexes, and granny flats, treats an ADU as its own service point in most cases. If the ADU sits within 150 feet of the main home, the new meter is typically installed next to the existing panel. Beyond that distance, it’s installed separately, closer to the unit itself — which usually means trenching for new underground conductors.

None of this is optional paperwork. It determines where the meter goes, how much conduit and trenching the project needs, and how much the utility coordination alone will add to the timeline.

There’s an important exception worth knowing about: SDG&E does allow shared service from the main home’s panel under certain conditions, most commonly for a junior ADU or a unit built solely for family use rather than as a rental. If a homeowner is trying to avoid the cost of a separate meter, this is the path to ask an electrician about early — before the floor plan and utility application are finalized, not after.

How Much Amperage Does a San Diego ADU Actually Need?

Sizing varies with square footage, appliance load, and whether the unit is fully electric (which most new California ADUs are required to be, per Title 24 energy standards). The chart below shows the amperage ranges electricians commonly design to for San Diego ADUs, based on unit size and load.

Notice that even a small ADU rarely gets by on the bare minimum. Most electricians recommend sizing a bit above the calculated minimum so the panel has room for a future EV charger, a heat pump, or added kitchen appliances without another service upgrade a few years down the road.

Load Calculations: The Step Homeowners Skip

The load calculation is what actually determines panel size — not a rule of thumb, not what the neighbor installed, and not what a contractor “usually” uses. It follows the National Electrical Code’s method for calculating combined loads on an existing dwelling (NEC 220.83), which accounts for the main house’s existing demand plus everything the new ADU will add: HVAC, water heating, cooking, lighting, and general receptacle load.

This is also where a lot of ADU budgets get their first real surprise. A property that looks like it has “plenty of panel” on paper can come up short once the ADU’s full load is added in, especially in older San Diego neighborhoods where the main house is still running on a 100-amp or 125-amp service from decades ago.

“The number one thing we tell ADU homeowners is: don’t finalize your floor plan before the load calculation is done. We’ve walked into projects where the panel was already boxed into a wall, and moving it added weeks to the schedule that could have been avoided with one conversation upfront.”

— Razmik, Electricians Service Team

The Permit Path Through the City of San Diego

ADU electrical work in San Diego is reviewed by the city’s Development Services Department alongside the rest of the building permit, not as a separate afterthought. State law requires the city to approve or deny a complete ADU application ministerially, generally within 60 days, which has sped up a process that used to take much longer. That timeline only holds, though, if the electrical plans — panel location, service size, meter placement, and load calculations — are complete and accurate on the first submittal.

Detached ADUs, particularly those requiring new trenching or a separate utility connection, may also need a right-of-way permit before the building permit can move forward. Skipping ahead on construction before that utility coordination is finalized is one of the more common causes of delay on San Diego ADU projects.

Properties within San Diego’s Coastal Overlay Zone add another layer to plan around. ADU electrical work itself isn’t usually the sticking point in the Coastal Zone, but the overall project timeline and setback rules can shift how and where a detached unit — and its electrical service — gets sited on the lot. If your property falls inside that zone, it’s worth confirming with Development Services early, since a redesign after the electrical rough-in is scheduled is far costlier than catching it during the plan-check stage.

Common Mistakes That Delay San Diego ADU Electrical Permits

A few patterns show up again and again in San Diego ADU projects that stall in plan check or run into unexpected change orders mid-build:

• Finalizing the floor plan before the load calculation. Panel and meter locations get locked into the design before anyone confirms the main house can actually support the added load.
• Assuming the existing panel has room. A 100-amp main panel that comfortably runs today’s household often has little to no spare capacity once an ADU’s full load is added.
• Underestimating trenching distance. If the ADU sits more than 150 feet from the main service, the separate-meter path usually means a longer, more expensive trench run than homeowners initially budget for.
• Not asking about shared service eligibility early. Some family-use JADUs qualify for shared service from the main panel, but that has to be established before the utility application is submitted, not requested afterward.
• Leaving EV charging and solar out of the conversation. Sizing the panel for today’s load only, with no room for a future charger or solar tie-in, often means paying for a second service upgrade a few years later.

What ADU Electrical Work Costs in San Diego

Costs vary widely depending on whether the project needs a simple subpanel or a full separate service with trenching. Panel upgrades in San Diego County generally run from the high hundreds into the low thousands for the electrical work itself, with larger service changes and separate-meter installations — including trenching and utility coordination — adding significantly more. Homeowners should get a firm, itemized quote before committing to a floor plan, since moving a panel or extending a trench route after the fact is far more expensive than planning around it from the start.

Rebates can sometimes help offset part of an ADU’s electrical scope, but only in specific circumstances — a panel upgrade tied to a larger electrification project like a heat pump water heater or heat-pump HVAC system may qualify for incentives, while a standalone panel upgrade generally does not. Program availability and amounts change often, so it’s worth checking current eligibility before assuming a specific rebate will apply.

It also helps to separate the electrician’s scope from the general contractor’s scope when comparing quotes. Some ADU cost estimates bundle panel work, trenching, and meter coordination into one line item; others break it out separately. Ask specifically what’s included — permit fees, utility coordination time, and final inspection follow-up can otherwise show up as surprise add-ons partway through the project.

Planning Ahead for EV Chargers and Solar

California’s Title 24 energy code pushes most new detached ADUs over 400 square feet toward solar-ready wiring, even when solar panels aren’t installed on day one. That typically means leaving conduit pathways and panel space available for a future system rather than closing everything up during construction.

The same logic applies to EV charging. Even homeowners who don’t currently own an electric vehicle are increasingly asking their electrician to rough in a dedicated circuit for a future Level 2 charger while the walls are still open. It’s a small add during construction and a much bigger, more disruptive retrofit later.

Why This Isn’t a DIY or Handyman-Level Job

Every step described here — the load calculation, the meter placement rules, the permit sequencing with the city, the utility coordination with SDG&E — depends on getting the electrical scope right the first time. Unlicensed or unpermitted electrical work on an ADU doesn’t just risk a failed inspection; it can hold up the entire project, since the city won’t sign off on a unit with electrical work that doesn’t match approved plans.

A licensed San Diego electrician who has coordinated ADU projects with SDG&E before can usually spot a sizing or placement problem during the design phase, long before it becomes an expensive change order mid-construction.

If you’re planning an ADU anywhere in San Diego, getting the electrical load calculation and panel plan settled early is the single most effective way to keep the project on schedule. Our team works directly with homeowners on electric panel upgrades and can also handle the EV charger wiring many ADU owners add during the same build.