Many single-family homes have detached garages, workshops, pool equipment buildings and storage structures, often called accessory buildings. Some larger homes may have separate guest houses and similar buildings located on the same property. Other names for these are guest suites, mother-in-law apartments, in-law suites, granny flats and casitas (in the Southwest). However, they are all considered by municipalities, building codes and the National Electrical Code to be “accessory buildings.”

As the cost of homes and property increases, more accessory buildings are being added to new and existing homes. They vary from very small and modest to very large and ornate structures.

Before attempting to add one of these to an existing property, check the building and fire codes as well as municipal and homeowner association rules and restrictions to ensure they can be added. They may be prohibited due to property lot size, distance from property lines, adjacent buildings and other similar limitations, especially if they are additions to existing buildings on the property.

The 2020 and 2023 NEC

There are also additional rules and requirements for one- and two-family dwellings in the 2020 and 2023 NEC that may affect the installation of accessory buildings. In the 2020 NEC, new Section 230.85 was added to require all service conductors for one- and two-family dwellings to terminate in an emergency disconnecting means, which was required to have a short-circuit current rating equal to or greater than the available fault current and be installed in a readily accessible outdoor location. The purpose of this emergency disconnecting means was to provide ready access for first responders, such as firefighters, so the power could be shut off to the dwelling unit from an exterior location. 

In addition, each emergency disconnecting means was required to be marked as one of the following:

“(1) EMERGENCY DISCONNECT, SERVICE DISCONNECT

“(2) Meter disconnects installed per 230.82(3) and marked EMERGENCY DISCONNECT, METER DISCONNECT, NOT SERVICE EQUIPMENT

“(3) Other listed disconnect switches or circuit breakers on the supply side of each service disconnect that are suitable for use as service equipment and marked as follows: EMERGENCY DISCONNECT, NOT SERVICE EQUIPMENT.”

Until this was added to the 2020 NEC, first responders and utility company personnel did not have outdoor access to safely remove power to the structure, so often turning power off meant entering the dwelling. In the 2020 NEC, this requirement only applied to the one- and two-family dwelling electrical service and did not apply to a dwelling supplied from a feeder.

In the 2023 NEC, Section 230.85 has been revised with more attention to the NEC Style Manual. New subsection (A) covers general requirements for dwelling unit emergency disconnects, with the location to be at a readily accessible location on or within sight of the dwelling unit. The disconnecting means must have a short-circuit current rating equal to or greater than the available fault current and, if there is more than one disconnecting means provided, the disconnecting means must be grouped in one location.

A new subsection (B) has been added requiring each disconnecting means to be a service disconnect; a meter disconnect integral to the meter-mounting equipment not marked as suitable only for use as service equipment installed in accordance with 230.82; or other listed disconnect switch or circuit breaker marked suitable for use as service equipment, but not as only for use as service equipment, installed on the supply side of each service disconnect. A new (C) has also been added stating that where service equipment is replaced, all requirements of 230.85 will apply to the new service.

New subsection (D) deals with identification of other isolation disconnects for other energy sources not adjacent to the emergency disconnects to have a plaque or directory identifying the location of all other isolation switches. The marking requirements provided in the paragraph above are now a new 230.85(E).

Section 225.41 has been added to cover emergency disconnect switches for one- and two-family dwelling units supplied by feeders. The text is similar to 230.85 and requires any accessory buildings that qualify as dwelling units to have emergency disconnect switches. The new Section 225.41 would not apply to buildings or structures that do not qualify or fall within the definitions of a one-family dwelling (a building that consists solely of one dwelling unit) or two-family dwelling (a building that consists of two dwelling units). 

These dwelling units must also fit within the definition of a dwelling unit as follows: “A single unit, providing complete and independent living facilities for one or more persons, including permanent provisions for living, sleeping, cooking, and sanitation.”

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