The Definitions That Matter
| Term | Working Definition | Regulatory Consequences in Maine |
|---|---|---|
| Dwelling unit NEC Art. 100 |
One or more rooms providing complete, independent living: permanent provisions for living, sleeping, cooking, and sanitation. | Triggers the dwelling-unit GFCI list 210.8(A), the broad AFCI list 210.12(B), receptacle spacing, and small-appliance circuit rules. |
| One-family (single-family) dwelling | A building consisting solely of one dwelling unit. | The only category where Maine's owner-occupant licensing and permit exceptions apply §1102-D · §1201-A(13); licensed electricians are exempt from the state permit here too. |
| Two-family dwelling | A building consisting solely of two dwelling units. | Still "residential" for most NEC purposes (e.g., outdoor emergency disconnect at services), but the owner-DIY exception does not apply — it's limited to single-family. |
| Multi-family dwelling | A building containing three or more dwelling units — the Maine triple-decker, converted Victorians, apartment blocks. | Licensed electricians and permits, full stop. Adds house loads, meter banks, service identification plaques 230.2(E) as amended, and dwelling-unit protection rules inside each unit. |
| Commercial / other occupancies | Everything that isn't a dwelling: retail, offices, restaurants, schools, healthcare, industrial. | Different GFCI regime 210.8(B) as ME-amended, targeted AFCI (dormitories, hotel guest rooms), engineered load calcs, and often design-build coordination with architects and fire marshals. |
Two Maine-specific wrinkles: the Board amended the "Dormitory Unit" definition, tightening which group-sleeping arrangements fall under dormitory AFCI rules — relevant to college towns and seasonal worker housing. And the licensing statute's exemptions repeatedly hinge on "single-family dwelling," so a camp with a rented ell or a house with a legal accessory apartment can silently move a project from DIY-permissible into licensed-only territory.
Mixed-Use and Edge Cases
Store below, apartments above
The classic Main Street block is both worlds at once: commercial rules in the storefront, dwelling-unit rules in the apartments, and building-level questions (services, meters, fire alarm) that need a contractor comfortable in both.
Home occupations
A workshop or home office inside your single-family home stays residential. Convert the barn into a customer-facing salon and the wiring in that space is commercial-occupancy work — and outside the owner-DIY exception.
Short-term rentals
A whole-home STR you don't occupy isn't "your bona fide personal abode." Owner-exemption arguments fail here; treat it like any other rental — licensed work only.
Rule of thumb
If anyone other than your own household sleeps, works, or shops under the roof, plan on a licensed electrician and a permit. The exemptions are drawn tightly around the owner-occupied single-family home.