Portland requires that an accessory dwelling unit have electrical circuits completely independent of the main house, sharing no loads with it, and the homeowner exemption that normally lets you do your own electrical work does not apply to an ADU at all. Those two rules catch more Portland ADU projects off guard than anything else, and both come straight from the city’s own ADU code guidance rather than from a contractor’s opinion.
Whether you are converting a basement, finishing a garage, or building a detached unit in the back yard, the electrical scope is bigger than most people budget for. Here is what the city actually requires, how a detached unit gets fed, when an ADU forces a service upgrade, and the one place the arc-fault rules work differently than they do on a normal panel job.
What Portland requires for ADU electrical
| Requirement | What it means in practice |
|---|---|
| Fully independent circuits | The ADU shares no loads with the main dwelling. Nothing in the ADU may be fed from a circuit that also serves the house, and vice versa. |
| Separate service or panel preferred | The city recommends the ADU be served by its own service or panel. Sharing the main panel is allowed only where a separate one is not feasible. |
| Shared panel must be accessible to both | If the main panel does serve both units, it has to sit in a common area with direct access from both units. A panel inside the main home’s living space does not qualify. |
| Licensed contractor, no exceptions | The homeowner exemption for doing your own electrical work does not apply to creating or altering an ADU. |
| Separate permits per structure | Detached buildings are permitted separately, and an ADU needs building plus trade permits including electrical. |
Does an ADU need its own electrical panel or service?
Portland’s guidance is that a separate service or panel is recommended, and that where that is not feasible the panel serving the main dwelling may be approved to serve both. So it is a preference rather than an absolute, but the fallback carries a condition that rules out a lot of houses.
That condition is access. A shared panel has to be located in a common area with direct access from both units. In practice this is where a lot of basement conversions run into trouble, because the existing panel sits inside what is about to become private living space for one unit or the other. A tenant cannot be expected to knock on the owner’s door to reset a breaker, and an inspector will not sign off on an arrangement where they would have to.
Separate panel for the ADU
A dedicated subpanel or service for the unit. Satisfies the independence requirement by design, keeps the tenant’s breakers reachable, and makes any future metering conversation simpler.
Sharing the main panel
Permitted where a separate panel is not feasible, but only if the panel sits in a common area both units can reach directly, and only if no circuit serves both units.
Whether a separate utility meter is involved is a separate question from the panel, and it is worth settling with the utility early rather than assuming. Metering policy is set by the utility, not by the electrical code, and it can affect how the service is laid out.
Planning an ADU in the Portland metro?
We handle the electrical scope, the load calculation, and the permit. Same-week scheduling for most projects.
Can I do the electrical work myself?
No, and this one is unusually clear-cut. Portland’s ADU code guidance states that all new electrical work shall be conducted by a licensed electrical contractor, and that exemptions allowing homeowners to perform electrical work on their own homes do not apply to work for the creation or alteration of an ADU.
That is worth understanding rather than just accepting, because the reasoning tells you something about the whole project. Oregon’s homeowner exemption applies to a residence that is not intended for sale, exchange, lease or rent. An ADU is very often built precisely to rent, which puts it outside the exemption by its nature. Combine that with the city’s explicit rule and there is no version of an ADU where the electrical is a DIY job.
This differs sharply from ordinary work on your own home. Replacing a receptacle or a light fixture in the house you live in falls under the Oregon maintenance exemption and does not even require a permit. The moment the work is creating or altering an ADU, none of that applies.
What “completely independent circuits” actually means
The requirement is that the ADU’s circuits share no loads with the main dwelling. It sounds simple and it is the single most common thing that fails inspection on conversions, because existing wiring rarely respects the line you are about to draw through the house.
Typical problems on a basement or garage conversion:
- A circuit that feeds both areas. One bedroom circuit upstairs that also picks up a basement outlet. That circuit has to be split.
- Shared lighting. A stairwell or hallway fixture wired into what will become the ADU’s circuit, or the reverse.
- The laundry or water heater. Anything the two units would both draw from needs a decision, and shared use generally is not acceptable.
- Smoke and CO alarms. Interconnection and power source requirements need to be worked out deliberately across two units rather than inherited from the old layout.
Realistically this means tracing existing circuits before design, not after demo. It is a large part of why an ADU conversion’s electrical scope routinely comes in above what homeowners expect, and why a walkthrough beats a phone quote.
Feeding a detached ADU
A detached unit in the back yard adds a feeder, a trench, and a disconnect to the scope.
The feeder and the trench
The feeder is sized from a load calculation for the unit, not from a rule of thumb. It typically runs underground from the main service or panel to the ADU. Minimum cover under the electrical code depends on the wiring method:
| Wiring method | Minimum cover |
|---|---|
| Rigid metal conduit or intermediate metal conduit | 6 inches |
| Nonmetallic raceway listed for direct burial, such as PVC | 18 inches |
| Direct burial cable without a raceway | 24 inches |
| 120V or less, GFCI protected, 20A or less branch circuit | 12 inches |
Cover is measured from the top of the conduit or cable to finished grade, so the trench itself has to be deeper than the number in the table. Oregon does not amend the minimum cover table, so these are the values that apply here. Trenching is also where a back yard job gets expensive in ways nobody plans for: mature root systems, existing irrigation, a concrete patio, or a sewer line in the path.
The disconnect at the ADU
A detached structure needs a disconnecting means for the conductors entering it, installed at a readily accessible location nearest the point of entrance. That is often a main breaker in the ADU’s subpanel, or a separate disconnect ahead of it. It is not optional, and it is a common miss on owner-designed plans.
Will an ADU force a service upgrade?
Sometimes, and a load calculation is the only honest way to answer it. Adding a full second dwelling means adding its heating, cooking, water heating, laundry and general load onto whatever service already exists. On a Portland home still running 100 amps, that frequently does not fit.
Before committing to the ADU budget, get the load calculation done. If the service needs upgrading, that is a substantial line item and you want it in the plan rather than discovered mid-project. Our Portland panel upgrade cost guide covers what that work runs and what drives the price, and the panel permit guide covers the permitting side.
The arc-fault rule that works differently for ADUs
This is a genuine exception worth flagging, because it runs opposite to what applies on a normal panel job.
On an existing Oregon home, replacing a panel does not require adding AFCI protection to existing circuits, and Oregon did not adopt the provision requiring AFCI when a receptacle is replaced. Those exemptions are real and they save homeowners money on ordinary upgrades.
Portland’s ADU guidance is explicit that when a new occupancy is created within existing space, the circuits are not considered “existing” and must have arc-fault protection. So a basement or garage conversion does not inherit the exemption that a straight panel swap enjoys. Budget for AFCI protection on the ADU’s circuits from the start.
The distinction is intent rather than hardware. Swapping equipment on circuits that already existed is one thing. Creating a new dwelling unit is new work, and new work is held to current requirements.
What Oregon does not require
Two items sometimes appear on ADU quotes that Oregon has not adopted, both from the article covering feeders to separate structures:
- Emergency disconnects. The requirement at 225.41 is listed as not adopted by the State of Oregon.
- Surge protection. The requirement at 225.42 is likewise listed as not adopted by the State of Oregon.
Neither is a bad thing to install if you want it. Surge protection in particular is cheap insurance on a unit full of electronics. The point is that in Oregon they are options rather than code obligations, so they should appear on a quote as choices you agreed to.
Permits, charges and sequence
An ADU needs building permits plus trade permits, electrical among them. Portland lets you combine the applications under one permit number or file the trade permits later, and detached structures are permitted separately from the main house.
Two budget items catch people out. System development charges can be substantial, and Portland offers an SDC waiver if you covenant not to use the ADU as a short term rental for ten years. That is a real decision with a long tail, so weigh it before you sign rather than at the counter. Second, the electrical scope on a conversion is usually larger than the visible work suggests, because of the circuit separation described above.
A workable sequence looks like this: load calculation and electrical scope during design, permits filed with the electrical scope already understood, service upgrade first if one is needed, then rough-in, inspection, finish, and final inspection. Getting the electrician involved during design rather than after framing is what keeps the service question from becoming a change order.
Frequently asked questions
Does an ADU need its own electrical panel in Portland?
Portland recommends that an ADU be served by a separate service or panel, and allows the main dwelling’s panel to serve both where a separate one is not feasible. If the panel is shared it must be located in a common area with direct access from both units. Regardless of which arrangement is used, the ADU’s circuits must be completely independent and share no loads with the main dwelling.
Can I do the electrical work on my own ADU?
No. Portland’s ADU code guidance states that all new electrical work shall be conducted by a licensed electrical contractor, and that the exemptions allowing homeowners to perform electrical work on their own homes do not apply to the creation or alteration of an ADU. Oregon’s homeowner exemption also excludes property intended for lease or rent, which most ADUs are. This is different from ordinary work on your own residence, where maintenance such as replacing a receptacle is exempt.
What does “circuits completely independent” mean for a basement conversion?
It means no circuit may serve both the ADU and the main house. On conversions this is the most common inspection problem, because existing wiring rarely follows the new unit boundary. Circuits that pick up outlets in both areas have to be split, shared stairwell or hallway lighting has to be resolved, and anything both units would draw from, such as laundry or a water heater, needs a decision. Tracing the existing circuits during design rather than after demolition is what keeps this from becoming a change order.
How deep does the feeder to a detached ADU have to be buried?
It depends on the wiring method. Under the minimum cover requirements, rigid metal conduit or intermediate metal conduit requires 6 inches, nonmetallic raceway listed for direct burial such as PVC requires 18 inches, and direct burial cable without a raceway requires 24 inches. A 120-volt or less GFCI-protected branch circuit rated 20 amps or less requires 12 inches. Cover is measured from the top of the conduit or cable to finished grade, so the trench is deeper than the listed number. Oregon does not amend this table.
Will building an ADU mean upgrading my electrical service?
Often, and only a load calculation answers it. An ADU adds a second dwelling’s heating, cooking, water heating, laundry and general load to your existing service. On a Portland home still running 100 amps that frequently does not fit. Get the load calculation done during design so a service upgrade is a planned line item rather than a mid-project surprise.
Do ADU circuits need AFCI protection even though panel swaps do not?
Yes, and this is an important exception. On an existing Oregon home, replacing a panel does not require adding arc-fault protection to existing circuits, and Oregon did not adopt the provision requiring AFCI on receptacle replacement. But Portland’s ADU guidance states that when a new occupancy is created within existing space, the circuits are not considered existing and must have AFCI protection. A conversion is treated as new work, so budget for it.
Does a detached ADU need its own disconnect?
Yes. Conductors entering a separate structure require a disconnecting means installed at a readily accessible location nearest the point of entrance. In practice this is usually a main breaker in the ADU’s subpanel, or a separate disconnect ahead of it. It is a frequent omission on owner-drawn plans and it will be caught at inspection.
Building an ADU in the Portland metro?
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