Look, we’ve all been there. You’re finally ready to turn that detached garage into something useful—a workshop, a home gym, or maybe even a small rental unit. You’ve picked out the insulation, you’ve got a plan for the walls, and then it hits you: the wiring. And not just any wiring, but the code requirements that come with a detached structure. It’s the part of the renovation nobody talks about at the hardware store, but it’s the one thing that can stop your project dead in its tracks.
The most important thing to know upfront is that a detached garage is treated as a separate structure by the National Electrical Code (NEC). That means you can’t just run an extension cord from the house or tap into the main panel without serious consideration. You need a dedicated feeder, proper grounding, and often a subpanel. If you get this wrong, you’re looking at failed inspections, fire risk, or at best, a lot of rework. Here are the key takeaways you need to hang onto.
Key Takeaways:
- A detached garage requires its own grounding electrode system (ground rods) unless it’s fed by a single branch circuit.
- You must install a disconnect switch at the garage—this is non-negotiable, even if you only have one circuit.
- The feeder from the house needs to be sized for the load, buried at least 18 inches deep (or run in conduit), and protected by an overcurrent device.
- GFCI protection is required on all 120-volt, 15- and 20-amp outlets in the garage, including those for appliances like a refrigerator or freezer.
- You cannot share a neutral on multi-wire branch circuits in separate buildings; each circuit needs its own neutral conductor.
The Grounding Problem Nobody Warns You About
This is where most DIYers and even some contractors trip up. The NEC requires a separate grounding electrode system for a detached garage. Why? Because the structure is physically separate from the house, and if lightning strikes or a fault occurs, the ground path needs to be local. You can’t rely on the ground wire coming back from the house panel.
In practice, this means driving at least one ground rod (two if the resistance is over 25 ohms) and connecting it to the garage subpanel’s grounding bus. We’ve seen people skip this step, thinking the ground wire in the feeder is enough. It’s not. The inspector will flag it, and you’ll be pulling out your trenching shovel again. The exception? If you’re feeding the garage with a single branch circuit (like one 20-amp circuit for lights), you don’t need a separate ground rod. But for any real renovation—think multiple circuits for tools, outlets, and appliances—you’re driving rods.
What About the Grounded (Neutral) Conductor?
Here’s a subtle point that causes real headaches. In the main house panel, the neutral and ground are bonded together. But in the detached garage subpanel, they must be kept separate. That means no bonding screw, no jumper between the neutral and ground bars. If you bond them in the garage, you create a parallel path for current on the ground wire, which can energize metal enclosures. We’ve seen this exact mistake cause a mild shock on a metal workbench. It’s not theoretical.
The Disconnect Requirement: More Than Just a Switch
Every detached garage needs a means of disconnecting all power. This can be a simple switch at the garage entrance, a breaker in the subpanel, or a separate disconnect outside. The key is that it must be within sight of the equipment it serves. If your subpanel is in the back corner of the garage, you probably need a disconnect at the door.
We had a customer who built a beautiful workshop, installed a 60-amp subpanel, and then realized the inspector wanted a disconnect at the entrance because the panel was hidden behind a shelving unit. It was a simple fix—a 60-amp rated switch—but it cost him an extra day and a return trip. Plan for this. Put your disconnect or main breaker at the garage entrance, and save yourself the headache.
Feeder Sizing and Burial Depth: The Physical Reality
Running power from the house to the garage is the most labor-intensive part. You’ve got a few options, and each has trade-offs.
Direct Burial vs. Conduit
Direct burial cable (like UF-B) is cheaper and faster, but it needs to be buried at least 24 inches deep. That’s a lot of digging. Conduit (PVC or metal) can be buried at 18 inches, but you have to pull the wire through it, which takes more planning and elbow grease. In our experience, if you’re running a larger feeder (60 amps or more), conduit is the way to go. It’s easier to pull larger wire, and you can always add circuits later without digging again.
Sizing the Feeder
You need to calculate the load. A typical garage with lights, a few outlets, and maybe a small welder or air compressor might need a 60-amp feeder. But if you’re planning a home gym with a mini-split, a refrigerator, and a TV, you’re looking at 100 amps. Don’t undersize it. We’ve seen people run a 30-amp feeder for a workshop, then add a heater and blow the breaker every winter. The cost difference in wire is small compared to the frustration.
Here’s a quick reference table comparing feeder options:
| Feeder Size | Typical Use Case | Wire Type & Cost (approx) | Burial Depth | Key Trade-off |
|---|---|---|---|---|
| 30 amp | Lights, a few outlets, small tools | 10/3 UF-B ($1.50/ft) | 24 inches | Cheap, but limits future expansion |
| 60 amp | Workshop, welder, air compressor | 6/3 UF-B or 6 AWG THHN in conduit ($2.50/ft) | 18-24 inches | Good balance of cost and capacity |
| 100 amp | Full garage conversion with HVAC, appliances | 3/3 with ground in 1.5″ PVC ($4.00/ft) | 18 inches | Expensive, but future-proof and allows for a subpanel |
GFCI and AFCI: The Overlooked Protection
The NEC now requires GFCI protection on all 120-volt outlets in garages. That includes outlets for garage door openers, refrigerators, and even the freezer you keep out there. We’ve had customers complain that their freezer trips the GFCI during a power surge. It happens. But there’s no exception for appliances in a garage. You can either use GFCI breakers in the subpanel or GFCI outlets. The breakers are cleaner if you have multiple outlets on one circuit.
AFCI protection is trickier. For new construction, the NEC requires AFCI on most circuits in dwelling units, but detached garages are often considered “other structures” and may not need AFCI. Check your local amendments. Some jurisdictions require it; others don’t. We’ve seen inspectors ask for it in garages that are finished as living space (like a guest house). Don’t assume.
The Subpanel Debate: When You Need One
If you’re running more than one circuit to the garage, you need a subpanel. It’s not optional. The subpanel gives you local overcurrent protection and makes it easy to add circuits later. We recommend a minimum 60-amp panel with at least 8 spaces. Even if you only need two circuits today, you’ll thank yourself later.
Mount the subpanel in a clean, accessible location. Not behind a workbench. Not in a corner where you’ll pile boxes. We’ve seen garages where the panel is buried behind stored lumber, and every time the homeowner needs to reset a breaker, they have to move half the garage. Put it near the garage door or at eye level on a clear wall.
A Note on Local Codes and Climate
The NEC is a baseline, but local amendments can change everything. In colder climates, the frost line affects burial depth. In areas with high lightning activity, grounding requirements might be stricter. Always check with your local building department before you start. We’ve seen people dig a 24-inch trench only to find out the local code requires 30 inches because of frost. That’s a lot of extra digging.
If you’re in an area with frequent power outages, consider adding a generator interlock at the garage subpanel. It’s a small addition that gives you backup power for your shop or living space. We’ve done this for several customers who work from home and need their tools running even when the grid goes down.
Common Mistakes We See Repeatedly
- Bonding the neutral in the subpanel. This is the number one mistake. It causes ground loops and can energize metal surfaces.
- Using too small a feeder. Everyone underestimates their future needs. Go bigger than you think you need.
- Forgetting the disconnect. It’s easy to overlook, but the inspector won’t.
- Not driving a ground rod. Even if you think the house ground is sufficient, it’s not for a detached structure.
- Running UF cable too shallow. The 24-inch requirement is often ignored by DIYers. Don’t risk it.
When to Call a Professional
Honestly, if you’ve never wired a subpanel or run a feeder, this is not the project to learn on. The cost of a mistake—fire, shock, failed inspection—is too high. We’re not saying you can’t do it, but we’ve seen too many homeowners spend twice as much fixing their own work as they would have paid a pro upfront.
If you’re in the Bay Area, where we work, the soil can be rocky, the frost line is shallow, and the inspectors are thorough. We’ve done dozens of garage conversions, and the ones that go smoothly are the ones where the homeowner called an electrician early. It’s not about ego; it’s about getting the job done right the first time. If you’re considering a full garage conversion, talk to an experienced ADU contractor who understands both the electrical and structural requirements.
The Bottom Line
Wiring a detached garage isn’t rocket science, but it’s unforgiving of shortcuts. The NEC is written for a reason, and local codes exist to address specific conditions. Take the time to get the grounding right, size your feeder properly, and install a disconnect. Your garage reno will be safer, more functional, and easier to sell if you ever move.
And if you’re tired of digging trenches and reading code books, there’s no shame in hiring someone who’s already done it a hundred times. We’ve seen the look on a homeowner’s face when the inspector passes their work on the first try. It’s worth every penny.
People Also Ask
Yes, Romex (NM-B cable) is generally allowed in a detached garage, provided the installation follows the National Electrical Code (NEC). For a detached garage, the cable must be properly protected from physical damage. This means if the Romex runs exposed along walls or ceilings below eight feet, it typically needs to be enclosed in conduit or installed within the wall cavity. Additionally, all connections must be made in approved junction boxes with covers. For specific local amendments or requirements, consulting a professional like A1 ADU Contractor can ensure your project meets all safety and code standards. Always verify with your local building department, as rules can vary by jurisdiction.
For a garage wiring project, the most critical code is the National Electrical Code (NEC), which requires all 120-volt, 15 and 20-amp circuits in garages to be protected by a Ground-Fault Circuit Interrupter (GFCI). This includes outlets for general use, workbenches, and even the refrigerator if it is plugged into a standard receptacle. Additionally, any switches and outlets must be installed at least 18 inches above the garage floor to avoid damage from water or minor flooding. Dedicated circuits are typically needed for major appliances like electric water heaters or EV chargers. For a thorough breakdown of these requirements, A1 ADU Contractor recommends reviewing the internal article titled How To Handle Electrical Wiring In Garage Renovations. Always consult your local building department, as amendments to the NEC can vary by jurisdiction.
The National Electrical Code (NEC) requires that a detached garage have its own grounding electrode system if it is supplied by a separate feeder or branch circuit. This typically means driving a ground rod at the garage and connecting it to the grounding bus in the subpanel. The NEC also mandates that a subpanel in a detached structure must have the grounded (neutral) conductor isolated from the equipment grounding conductor; they can only be bonded at the main service panel. This prevents dangerous current from traveling on metal enclosures. For a garage conversion project, these requirements are critical for safety. At A1 ADU Contractor, we always follow these standards. For related insights, our internal article titled Adding Plumbing To Your Garage Conversion: What To Know covers these plumbing and electrical integration points in detail.
Yes, a subpanel in a detached garage typically requires a main breaker, but the specific code requirement depends on the number of disconnects and the panel's location. According to the National Electrical Code (NEC), a detached structure with a subpanel must have a means to disconnect all power at the building. If the subpanel has six or fewer breakers, a main breaker is not strictly required, as each breaker can serve as a disconnect. However, for safety and convenience, installing a main breaker is strongly recommended. It allows you to shut off all power to the garage from one point, which simplifies maintenance and emergency response. At A1 ADU Contractor, we always advise including a main breaker in detached garage subpanels to meet code and ensure safe, reliable operation.
