Does an ADU Need Its Own Electrical Panel or Meter?

Does an ADU need its own panel and its own meter?

An ADU needs its own electrical panel, a subpanel in or on the unit, so whoever lives there can reach their own breakers. A separate utility meter is usually your choice. One meter with a subpanel is the common, less expensive route. The bigger question is whether your main service can carry a second home.

That last part is why the electrical line in your builder’s estimate can look so large. Capacity is where the money goes.

Why the ADU gets its own panel

Picture a breaker tripping in the unit at 10 p.m. Your tenant, or your mother living out back, shouldn’t have to knock on your door and walk through your garage to reset it. The occupant needs access to their own breakers, so the ADU gets a panel of its own.

With one shared meter, that panel is a subpanel. It doesn’t connect to the utility directly. A feeder cable runs from a breaker in your main panel to the ADU, and the subpanel splits that power into the unit’s circuits. Our post on what a subpanel is and when you need one covers how they work in more detail.

For a detached ADU, a few more pieces come with it:

• The feeder runs underground in conduit, with four wires: two hots, a neutral and a ground.
• The ADU gets its own grounding electrode at the building.
• It also needs a disconnect, so the unit’s power can be shut off at the unit.

One meter or two: ADU electrical requirements for billing

Both routes work. They differ in cost, timing and who gets the bill.

Rules for a second service vary by utility, so ask yours early if separate billing matters to you.

The question nobody asks early enough: can your service carry it?

An ADU is a small house. Give it an electric range, a heat pump or mini split, a water heater and a washer and dryer, and you’ve added a lot of load to your property. New ADUs are increasingly built all-electric, so that list is the norm, not the worst case.

A load calculation for the main house plus the ADU comes first. It adds up what both homes can draw and compares that with what your service can deliver. A 100-amp main service usually can’t carry both, and many ADU projects end up needing a service upgrade to 200 amps or more. If you’re unsure where your home stands now, our guide on when to upgrade a 100-amp panel to 200 amps is a good place to start.

Garage conversions

Converting a garage feels simpler because the building already has power. Usually that’s a single circuit, and it won’t run a kitchen, a bathroom and air conditioning. Plan on new wiring and a subpanel, the same as a new build.

Start the electrical plan when design starts

A service upgrade involves the utility, and that can take weeks or longer. If nobody looks at your service until framing is done, the electrical work can hold up the whole project. Bring an electrician in while the plans are still on paper. The ADU’s electrical work is part of your building permit and gets inspected along with everything else.

Infiniti Electric is a licensed and insured contractor in Riverside, and we can run the load calculation, check your main electrical panel and tell you honestly whether you need an upgrade. To get started, contact us with your ADU plans.

More ADU panel and service questions