Before You Finalize ADU Plans: Electrical Load and Service Planning in Sacramento County

For an ADU, electrical decisions should be made before the floor plan and equipment selections are locked. ADU electrical planning in Sacramento County should start with a load calculation, a review of the existing electrical service, a plan for how power will reach the unit, and early utility coordination when the project affects the service. Those decisions can change panel size, trenching, meter placement, equipment locations, and the overall construction scope.

At TNT Electric Co., we work on residential electrical systems throughout Sacramento and Citrus Heights, including electrical panel upgrades and electrical planning for new construction and remodels. Looking at the electrical side early gives the designer, homeowner, contractor, and electrician a much clearer picture of what the ADU will require before construction begins.

Start ADU Electrical Planning in Sacramento County With the Load

An ADU adds an entirely new set of electrical loads to a property. Square footage matters, but it doesn’t tell the whole story.

The equipment going into the unit has a much larger effect on the electrical design. An all-electric ADU with electric water heating, cooking, HVAC, laundry equipment, and several dedicated appliance circuits will have different requirements from a small unit with a lighter electrical load.

That is why equipment decisions should happen early.

An electrician needs to know what the ADU is expected to power. That usually means reviewing the planned HVAC equipment, water heater, cooking appliances, laundry setup, kitchen equipment, lighting, receptacles, and any larger dedicated loads.

Future plans matter too. If the property owner expects to add EV charging near the ADU or expand the electrical system later, it makes sense to account for that while the project is still on paper.

A load calculation puts numbers behind those plans. It evaluates the existing electrical demand and the additional load the ADU will place on the property. From there, the electrician can determine whether the current service is adequate or whether the project requires changes elsewhere in the system.

An Open Breaker Space Doesn’t Mean the Service Has Enough Capacity

Homeowners sometimes look inside the main panel, see an unused breaker position, and assume there is room to power an ADU.

Breaker space and electrical capacity are different questions.

The panel might have open spaces while the home’s calculated electrical load is already approaching the limits of the service. The opposite situation also occurs. A panel can run out of physical breaker positions even though the service still has usable capacity.

The main breaker rating alone doesn’t settle the issue either. A 200-amp service isn’t automatically sufficient for every ADU project, just as an existing 100-amp service doesn’t automatically mean an upgrade will be necessary. The decision depends on the property’s calculated load and the electrical equipment being added.

TNT Electric evaluates electrical demand as part of panel and subpanel planning. Our subpanel installation service also notes an important distinction: adding a subpanel creates additional distribution and circuit space, but the subpanel still receives its power from the main electrical system. It doesn’t increase the property’s total service capacity by itself.

That distinction matters on an ADU project. If the existing service doesn’t have enough capacity for the additional load, adding another panel doesn’t solve the underlying capacity issue.

Decide How the ADU Will Receive Power

Once the expected load is understood, the next question is how electricity will reach the unit.

An attached ADU presents a different electrical layout from a detached structure at the back of a lot. Distance from the main service, existing utility equipment, underground routing, overhead lines, and the proposed location of the ADU all affect the design.

For some projects, a feeder from the main electrical system to a subpanel at the ADU may make sense. Other projects involve changes to the property’s service or metering arrangement that require coordination with the electric utility.

The route matters too.

A detached ADU may require underground conduit between structures. The electrician and project team need to know where that route can reasonably go before landscaping, concrete, drainage features, or other site improvements make the path more complicated.

SMUD specifically advises customers planning ADUs to address electric-service questions early because the location and design of the unit affect how service can be provided. Its current Design & Construction Services guidance also directs ADU projects to utility planning resources intended to reduce redesigns and project delays.

Waiting until the ADU is framed to settle those questions leaves far fewer options.

Coordinate the Electrical Plan With the Site Plan

Electrical planning shouldn’t happen separately from the site plan.

The electrician needs to understand where the ADU will sit in relation to the existing house, electrical service, driveway, fences, utility equipment, and accessible working areas. A proposed panel location that looks reasonable on a floor plan might create problems once the actual site conditions are considered.

Detached units deserve particular attention because power has to travel between structures. The shortest route isn’t always the route that works best once existing utilities and other site constraints are considered.

Meter and panel locations also need to stay accessible for the required work and future service. Moving electrical equipment later in the design process can affect conduit lengths, feeder sizing, excavation, wall layouts, and coordination with other trades.

This is one reason we prefer to review the existing electrical system before the ADU plans are treated as final.

Permit Requirements Depend on the Property’s Jurisdiction

“Sacramento County” can describe the geographic area without identifying the agency that will actually review a project.

A property inside the City of Sacramento, Citrus Heights, or another incorporated city follows that jurisdiction’s permitting process. Sacramento County’s Building Permits & Inspection Division handles projects in unincorporated areas.

For projects under Sacramento County jurisdiction, the County states that ADUs require permits and that construction projects submitted on or after January 1, 2026 must follow the current 2025 California Building Standards Code. The County also offers shelf-ready detached ADU plans, but those plans are specifically for properties in unincorporated Sacramento County.

A preapproved or shelf-ready building plan also doesn’t mean every property has identical electrical conditions. The existing service, utility connection, panel location, and site layout still need to work for the individual property.

Before finalizing the electrical scope, confirm which building department has jurisdiction over the address and which utility serves the property.

Set Major Equipment Choices Before the Electrical Plans Are Finished

Changing an appliance after electrical plans are complete sometimes creates more work than homeowners expect.

Suppose an early ADU plan assumes one type of water heater, but the final equipment has a substantially different electrical requirement. The circuit, breaker, conductor sizing, panel schedule, and overall load calculation may need another look.

The same issue applies to HVAC systems, ranges, dryers, and other higher-demand equipment.

You don’t necessarily need final model numbers for every light fixture before an electrician begins planning. Larger electrical loads are different. Their specifications directly affect circuit and service calculations.

Before the electrical design is finalized, try to settle:

• The heating and cooling equipment
• Water-heating type and electrical specifications
• Cooking equipment
• Laundry equipment
• Any planned EV charging on the property
• Other equipment that requires a dedicated or higher-amperage circuit

That information gives the electrical plan something concrete to work from instead of relying on assumptions that may change later.

What Should You Have Ready for an ADU Electrical Review?

The electrician doesn’t need a completed building to start evaluating the project. In fact, earlier is usually better.

Bring whatever plans exist, even if they’re preliminary. A site plan is especially useful for a detached ADU because it shows the relationship between the new structure and the existing house.

It also helps to gather:

• A preliminary floor plan and site plan
• Information about the existing main electrical panel
• A list of the larger appliances and mechanical equipment planned for the ADU
• Approximate locations for the ADU panel and major equipment
• Any future electrical projects already being considered for the property
• Information about existing overhead or underground utility service, if known

Don’t remove the panel cover or inspect energized equipment yourself to collect information. A photo of the exterior panel and its visible labels is enough to start the conversation. The electrician can inspect the electrical system directly when needed.

A Subpanel and a Service Upgrade Solve Different Problems

This distinction is worth resolving before an ADU budget is finalized.

A subpanel distributes power to additional circuits. It works well in many additions and detached structures because the new area gets its own convenient electrical distribution point.

A service upgrade addresses the amount of electrical capacity available to the property.

Some ADU projects need a subpanel without a service upgrade. Another property may need service work because the calculated load exceeds what the existing system should support. The layout and existing equipment determine the actual scope.

Treating every ADU as though it requires the same electrical package can lead to unnecessary work in one house and inadequate planning in another.

The calculation comes first. The equipment choice follows from what the project actually needs.

Plan the Electrical Scope Before Construction Starts

The best time to discover that an ADU affects the main service is before excavation, framing, and finish work are underway.

Early electrical planning lets the project team determine the expected load, evaluate the existing panel and service, choose a practical distribution method, and identify utility coordination that belongs in the schedule.

If you’re planning an ADU in Sacramento, Citrus Heights, or a nearby community, contact TNT Electric Co. while the project is still in the planning stage. We can review the existing electrical system and planned loads so the electrical scope reflects the ADU you’re actually building. TNT Electric Co. is a licensed electrical contractor based in Citrus Heights and serves Sacramento and surrounding communities.