Almost every detached garage starts the same way: a single extension cord snaked across the yard for a light and a battery charger. It works until it does not. Then come the trips, the cord that has been rained on all winter, and the realisation that a workshop, a freezer, a car lift or an EV charger was never going to run off it.
Wiring a detached structure properly is one of the more satisfying jobs on a property because it turns a storage box into a usable room. It is also a permitted job with real requirements, and the decisions made at the start determine what you can do out there for the next thirty years.
Start with what the building will actually do
This is the step that costs people money when they skip it. The conductors and the subpanel get sized once. Adding capacity later means digging the trench again.
Think past today's use and total up the realistic worst case: lighting, general receptacles, and then the heavy items. A compressor, a welder, a table saw, a mini-split for heating and cooling, a second refrigerator or freezer, a car lift, an EV charger. Each of those is a substantial load, and several of them together change the answer completely.
A garage that will only ever hold a car, a light and a couple of outlets is a modest job. A garage that becomes a workshop with a welder and an EV charger is closer to wiring a small house — and the difference between those two is mostly decided in the first conversation.
Subpanel or a single circuit?
There are two ways to feed a detached building, and they are not equivalent.
A single circuit
One circuit run out to the garage, feeding a light and a few receptacles. It is the cheaper option and it is genuinely appropriate for a building that will never be more than storage. The limitation is absolute: one circuit is one circuit, and everything out there shares it.
A subpanel
A feeder run to a small panel in the garage, which then distributes several circuits locally. This is the right answer for anything resembling a workshop. It gives you separate circuits for lighting, general outlets and heavy tools, so a saw starting up does not dim the lights or trip the freezer, and it gives you a local disconnect and room to add circuits later without touching the trench.
For most people who are asking the question at all, a subpanel is the honest recommendation. The incremental cost at the time of installation is small compared to doing the job twice.
Getting the power out there
The run itself is usually the largest part of the job, and there are two routes.
**Underground** is what most people choose and what most people should choose. It is invisible, out of the weather and out of the way of vehicles. It means a trench at a required depth, conduit or direct-burial cable rated for the purpose, and a warning ribbon above the run so the next person with a shovel gets a warning. The depth requirement varies with the wiring method and whether it passes under a driveway.
**Overhead** avoids the trench but brings its own rules about clearance above the ground, above driveways and away from windows and doors. It is usually the choice when the trench would cross mature tree roots, hardscape or a septic field.
One detail worth knowing, because it surprises people: distance costs money in copper. Voltage drop over a long run means the conductors have to be sized up — a 150-foot run may need noticeably larger wire than a 40-foot run carrying the identical load. If the garage is a long way from the house, that is a real line item, and it is another reason to size the feeder generously the first time.
The requirements that catch people out
A detached building is not simply an extension of the house, and a few rules apply specifically to it.
- **A separate grounding electrode.** A detached structure generally needs its own ground rod system, bonded correctly at the subpanel. This is one of the most commonly missed items in unpermitted work.
- **Neutrals and grounds kept separate.** In a detached subpanel the neutral bar must be isolated from the ground bar, unlike the main panel at the house. Getting this backwards is a classic and genuinely hazardous mistake.
- **A disconnecting means.** There has to be a way to kill power to the building at the building.
- **GFCI protection for garage receptacles**, which has been required for a long time and catches people restoring older detached garages.
- **Damp and wet location fittings** wherever the work is exposed, including any receptacle on an exterior wall.
Lighting, while the walls are open
If the garage is unfinished, this is the cheapest it will ever be to do the lighting properly. Two things are worth doing.
First, light the space for work rather than for storage. Linear LED fixtures laid out across the ceiling give even light with no shadow under the car or across the bench — a single bulb in the middle of the ceiling puts the shadow exactly where your hands are.
Second, put switching where you will use it: at the pedestrian door and at the vehicle door, so you are never crossing a dark garage to reach a switch. Add exterior lighting on the approach while the conduit is already going that way, and consider a motion sensor on the outside fixture.
Permits, and why they matter more here than usual
This is permitted work. A trench, a feeder and a subpanel on a detached structure will be inspected, and that is a good thing for two reasons beyond the obvious safety one.
The first is insurance. Unpermitted electrical work on an outbuilding is a known reason for a claim to be reduced or refused after a fire.
The second is resale. Buyers' inspectors look at detached structures specifically because they are where unpermitted work accumulates. A garage with a properly permitted subpanel is an asset in a sale; one with a mystery feeder and no paperwork becomes a negotiating point against you.
What this looks like on the Central Coast
A lot of the detached garages and shops around Atascadero, Templeton and Paso Robles are older structures on larger lots, which means longer runs and frequently an existing feed that was added informally years ago. Two things come up again and again: a run that was never sized for what the building is now used for, and a subpanel with the neutral and ground bonded together because whoever installed it wired it like a main panel.
Both are fixable. Neither is something to leave alone once you know about it. If you are planning a shop, a lift, an EV charger or just want the extension cord gone for good, we will size it for what you actually intend to do out there, pull the permit and leave you with a building you can use.
Have a question about your own home? Good Neighbors Electric is here to help across Atascadero and the Central Coast. Call (805) 610-5530 or request a free estimate.