Wiring a Detached Garage or ADU in Southern Maine: Trenching, Subpanels, and 2026 Code Rules
Planning a detached garage, workshop, or accessory dwelling unit in Saco, Biddeford, Portland, Scarborough, Kennebunk, Gorham, Windham, or Westbrook? Electrical planning should happen before excavation and framing begin.
The short answer is yes: you can make the process straightforward when the feeder, trench, subpanel, and future loads are planned together.
Maine’s 2026 electrical code applies to electrical installations beginning on or after July 1, 2026. That means a new garage or ADU started now should be reviewed under the 2026 National Electrical Code (NEC), Maine amendments, and local requirements.
Our team at Downeast Electrical Services helps homeowners plan new construction wiring so the work is safe, practical, and done once instead of being opened up again later.
Important: Electrical requirements can vary by project classification and local Authority Having Jurisdiction (AHJ). Always confirm the final requirements with your local inspector and a licensed electrician.
Step 1: Decide what the building needs before you trench
A detached garage used only for lights and a few receptacles has different electrical needs than a workshop or ADU.
Before choosing a feeder size, make a list of current and future loads, including:
General lighting and receptacles
Garage door openers
Mini-splits or heat pumps
Electric water heating
Kitchen appliances in an ADU
Laundry equipment
Air compressors and welders
Table saws or other workshop equipment
A Level 2 EV charger
Outdoor lighting and receptacles
Future tools or equipment
This list helps your electrician complete a load calculation for the main service and the detached building. A panel with open breaker spaces is not necessarily a panel with enough capacity.
For example, an ADU with electric heat, an electric range, water heating, and an EV charger may require significantly more capacity than a storage garage. Planning for those loads early can help you avoid a second trench, a larger excavation, or a service upgrade later.
Our service upgrade and panel services can help determine whether your existing electrical service can support the project.
Step 2: Plan the underground feeder and trench
Most detached buildings receive power through an underground feeder from the home’s main service or another approved source.
A common modern approach uses individual feeder conductors rated for wet locations inside PVC conduit. Direct-buried cable may also be possible, depending on the design and local approval.
Typical trench depths
Under NEC Table 300.5, common minimum cover requirements are:
Direct-buried cable: typically 24 inches of cover in a yard
PVC conduit with feeder conductors: typically 18 inches of cover in a yard
Rigid metal conduit: may require less cover in some locations
Under a residential driveway: requirements can vary by wiring method and location
“Cover” means the distance from finished grade to the top of the cable or conduit. It does not mean the depth to the bottom of the trench.
For example, if the conduit requires 18 inches of cover and the conduit is approximately 2 inches in diameter, the trench bottom may need to be about 20 inches below finished grade. The final depth depends on the wiring method, surface above the trench, and local requirements.
Call Dig Safe before excavation
Before trenching, contact Dig Safe by calling 811. Existing electrical, gas, water, telecommunications, and other utilities must be located before excavation begins.
Your electrician or excavation contractor should also consider:
The shortest practical route
Driveways and future hardscaping
Drainage and grading
Frost and soil conditions
Utility crossings
Conduit size for future capacity
A pull string for possible future conductors
Installing a slightly larger conduit while the trench is open can be a practical investment. It does not automatically provide more electrical capacity, but it can make future work easier if the service and panels can support it.
Step 3: Install the detached-building subpanel correctly
A detached garage or ADU will generally have a subpanel supplied by a feeder. A new feeder typically includes four conductors:
Two ungrounded conductors, often called the hot conductors
One grounded conductor, or neutral
One equipment grounding conductor
The detached-building subpanel must be configured correctly:
The neutral bar is isolated from the panel enclosure.
The equipment grounding bar is bonded to the enclosure.
The equipment grounding conductor connects back to the source equipment.
Neutral and ground are not bonded together again in the detached subpanel.
A grounding electrode system is installed at the detached building when required.
Depending on the site and building design, the grounding electrode system may include ground rods or a concrete-encased electrode.
This is one of the most important reasons to use a licensed electrician. Incorrect neutral and grounding connections can create objectionable current on metal parts and cause inspection or safety problems.
Step 4: Treat an ADU as a separate dwelling unit
Maine’s Electricians’ Examining Board has stated that an ADU is considered a multifamily dwelling for electrical purposes, even if it is described as an in-law apartment or guest suite.
That classification affects the design.
An ADU should have circuits dedicated to the loads within or associated with that unit. In practical terms, this usually means:
Separate lighting and receptacle circuits
Dedicated kitchen appliance circuits
Dedicated bathroom and laundry circuits
Clearly identified panel spaces
Overcurrent devices that occupants can access as required
No casual sharing of circuits between the main house and ADU
The electrical panel does not always need to be physically inside the ADU, but access and circuit arrangement must satisfy the applicable code and local inspector.
If the building includes both a garage and an ADU, your electrician can help determine whether one properly sized feeder and coordinated panel arrangement is appropriate, or whether separate service or metering should be considered.
Step 5: Plan AFCI and GFCI protection under the 2026 code
The 2026 electrical code in Maine includes important safety requirements for new construction wiring and altered circuits.
AFCI protection
AFCI protection helps detect dangerous arcing that can occur when wiring is damaged, loose, pinched, or improperly connected.
In an ADU, expect AFCI protection on many new or altered 120-volt, 15- and 20-amp circuits supplying outlets in areas such as:
Bedrooms
Living rooms and family rooms
Kitchens and dining areas
Hallways and closets
Laundry areas
Dens and similar living spaces
AFCI protection may be provided by an AFCI breaker, an approved AFCI device, or a dual-function AFCI/GFCI breaker, depending on the circuit and installation.
GFCI protection
GFCI protection is commonly required for receptacles and equipment in areas where people may encounter moisture or grounded surfaces.
In a detached garage or ADU, carefully plan for GFCI protection at:
Garage receptacles
Outdoor receptacles
Kitchen countertop receptacles
Bathroom receptacles
Laundry areas
Receptacles near sinks
Unfinished basements or crawl spaces
Certain outdoor HVAC equipment
The 2026 rules also expand attention to receptacles near indoor sinks. In addition, Maine’s temporary exception involving certain listed outdoor HVAC equipment expired on September 1, 2026. If your project includes a new mini-split, heat pump, or outdoor condenser, ask your electrician how the current rule applies to the specific equipment and installation date.
Our ductless mini-split services can be coordinated with your garage or ADU electrical plan.
Step 6: Make room for an EV charger
The 2026 NEC includes an EV-ready outlet requirement for new one- and two-family dwellings. However, Maine guidance classifies ADUs as multifamily dwelling units, so the requirement may not automatically apply to every ADU built on a single-family property.
Local building, zoning, or development requirements may also affect the answer. Confirm the project classification with your town before construction.
Even when an EV-ready outlet is not required, installing future-ready wiring can be a smart choice. A typical Level 2 charger may need a dedicated 240-volt circuit, often in the 40- to 50-amp range, depending on the charger.
Planning should include:
The charger’s installation instructions
Available service capacity
Feeder and subpanel capacity
Conduit routing to the parking area
Weather protection
EV-listed receptacles where required
GFCI protection for EV charging receptacles
Load management if multiple high-demand loads are present
A hardwired charger may have different requirements than a plug-in charger. The manufacturer’s instructions, equipment listing, NEC requirements, Maine amendments, and local inspection practices all matter.
See our EV charger installation services before ordering equipment.
Step 7: Get permits and schedule inspections
A new feeder, detached-building subpanel, garage wiring, or ADU electrical system generally requires an electrical permit before work begins.
Depending on the municipality, the permit may be handled through the town or through the Maine Electricians’ Examining Board. Our electrical permitting service includes submitting permit information to local municipalities and providing required documents. Additional drawings or municipal requirements may involve extra services.
A typical project may include:
Planning and load review
Permit application
Dig Safe notification
Trenching and conduit installation
Rough electrical inspection before walls are closed or the trench is backfilled
Panel and device installation
Final inspection
Energizing the new building after approval
Do not cover the trench until the inspector has confirmed whether an inspection is required. Taking photographs before backfill can also be helpful for your project records, but photographs do not replace an inspection.
A simple Southern Maine planning checklist
Before construction starts in Saco, Biddeford, Portland, Scarborough, Kennebunk, Gorham, Windham, Westbrook, or nearby communities:
Confirm which code edition applies based on the installation start date.
Contact the local code office or electrical inspector.
Call Dig Safe before excavation.
Decide whether the feeder will use direct-buried cable or conduit.
Plan the trench based on required cover, not just trench depth.
Complete a load calculation for the house, garage, and ADU.
Keep the detached-building neutral isolated from ground.
Install the required grounding electrode system.
Plan AFCI and GFCI protection before ordering panels.
Reserve capacity for an EV charger, workshop, or future mini-split.
Arrange rough and final inspections.
Use a licensed electrician familiar with Maine requirements.
The bottom line
A detached garage or ADU is much easier to wire when the electrical system is designed before excavation and framing.
The key points are:
PVC conduit commonly requires 18 inches of cover in a typical yard.
Direct-buried cable commonly requires 24 inches of cover.
A detached-building feeder generally uses four conductors.
The subpanel neutral must remain isolated from the equipment grounding system.
ADUs need dedicated circuits and appropriate occupant access to overcurrent devices.
AFCI and GFCI protection should be planned from the beginning.
EV-ready requirements depend on the dwelling classification and local rules.
Permits and inspections are part of doing the work safely and correctly.
If you are comparing electrical companies in Maine or looking for experienced electricians in Maine for a garage, workshop, or ADU, Downeast Electrical Services is here to help. We can review your plans, explain the practical choices, and help make your project seamless and hassle-free.
Contact Downeast Electrical Services to discuss your Southern Maine project before trenching begins.
Stay tuned for more informative blog posts from us.
Frequently asked questions
How deep should an electrical trench be in Maine?
For a typical residential yard, direct-buried cable commonly requires 24 inches of cover, while feeder conductors installed in PVC conduit commonly require 18 inches of cover. The measurement is taken to the top of the cable or conduit. Driveways, roadways, and special locations may require different depths.
Does a detached garage need its own subpanel?
A detached garage commonly receives power through a feeder connected to a subpanel in the garage. The design depends on the building’s loads, distance, service capacity, and local requirements. The neutral and equipment grounding system must be configured correctly.
Does an ADU need a separate electrical panel?
An ADU needs circuits dedicated to the loads serving that dwelling unit, and occupants must have the access required by code to the applicable overcurrent devices. A separate panel is often the clearest solution, but the final arrangement should be reviewed by a licensed electrician and the local inspector.
Is EV-ready parking required for every ADU in Maine?
Not automatically. The 2026 NEC includes an EV-ready outlet requirement for new one- and two-family dwellings, while Maine guidance classifies ADUs as multifamily dwelling units. Local building or zoning requirements may differ, so confirm the project classification with your municipality.
Do I need a permit to wire a detached garage?
Yes, a new feeder, subpanel, and building wiring generally require an electrical permit before work begins. Permit procedures vary by municipality and project type.
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