Where can the electrical panel go in an ADU?

Almost anywhere that gives it the required clear working space and keeps it out of prohibited spots. For a typical 120/240-volt panel, the California Electrical Code requires a clear space in front at least 30 inches wide (or the panel's width, if wider), 3 feet deep and 6½ feet high, and it keeps breakers out of bathrooms and away from easily ignitible material such as the contents of clothes closets.

Working space rules (Section 110.26)

• Depth: at least 3 feet of clear space in front, for equipment at 150 volts or less to ground.
• Width: the width of the panel or 30 inches, whichever is greater, and the door must be able to open at least 90 degrees.
• Height: clear from the floor to 6½ feet or the height of the equipment, whichever is greater.
• Level floor: the floor or grade in the working space must be kept clear and as level and flat as practical.
• No storage: the working space can't be used for storage.
• Dedicated space: the zone the width and depth of the panel, from the floor to 6 feet above the panel or to the structural ceiling (whichever is lower), must stay free of pipes, ducts and other equipment foreign to the electrical installation.
• Lighting: the working space around an indoor panel must be illuminated.

Places to avoid

• Bathrooms. Breakers are not allowed in dwelling unit bathrooms.
• Clothes closets and other spots near easily ignitible material.
• Inside cabinets or behind appliances and counters, where the working space can't be maintained.
• Locked spaces the ADU occupant can't reach. The code requires each occupant to have ready access to the overcurrent devices protecting the conductors that supply their unit, so ADU breakers generally belong in or on the ADU, not locked inside the main house.

Indoor or outdoor

Both can work. An outdoor panel must be rated for the location, and its working space must be on stable, level ground. An exterior wall also has to work with side-yard setbacks and stay clear of the gas meter area, where utilities set their own clearance zones. For a detached ADU fed from the main house, the feeder disconnect must be at a readily accessible location nearest where the conductors enter the building, so the panel or disconnect usually ends up on or just inside the wall where the feeder arrives.

Garage conversions and existing spaces

In existing dwelling units, the code allows panels of 200 amps or less in spaces with less than 6½ feet of headroom. That can help in a garage conversion with a low soffit, but the depth and width rules still apply.

What this means for your electrical plan

The floor plan should show the panel location with its working space drawn and dimensioned, the dedicated space kept clear of ducts and plumbing, and the point where the feeder enters. Resolving this on the drawings avoids moving the panel after cabinets and mechanical equipment are placed. See how a detached ADU subpanel works, reusing garage electrical in a conversion and our electrical plans.

Sources: dgs.ca.gov, ecmweb.com, forums.mikeholt.com.