Running power from your home to a detached garage requires careful planning and a correctly installed subpanel. This approach improves safety, code compliance, and convenience when you need electricity for tools, lighting, or a small workshop.
Use this guide to understand key choices, local code expectations, and best practices for adding a subpanel to a detached garage.
| Phase | Key Task | Typical Time | When to Call Pro |
|---|---|---|---|
| Design | Load calculation, feeder sizing, route planning | 1–3 hours | Large motor loads, long runs, limited space |
| Permits & Inspection | Apply, label, schedule, corrections | 1–7 days | Code uncertainty, municipal review |
| Installation | Trench or conduit, feeder pull, panel mounting, wiring | 4–8 hours | Low voltage experience, complex raceway |
| Testing & Cleanup | Verify GFCI/AFCI as required, test loads, restore site | 1–2 hours | Unstable readings, persistent faults |
Planning the Feeder and Breaker Size
Calculate Loads and Select Conductors
Start by listing every device you expect to run in the garage, including tools, lighting, and any small appliances. Add up the running watts and identify any large loads like a table saw or air compressor that start at high inrush current.
Use the total load to size the feeder conductors and main breaker in the subpanel, ensuring they match or exceed the requirements of your local electrical code and the main panel's spare space.
Routing and Protecting the Circuit
Choose Conduit or Direct Burial for Long Runs
For a flexible and serviceable installation, pull THHN or XHHW copper conductors through schedule 40 PVC conduit from your house to the garage subpanel location.
If local rules allow and the run is straightforward, you may use direct burial cable with proper conduit for physical protection at surface crossings.
Mounting and Wiring the Subpanel
Secure the Panel and Connect the Main Lugs
Mount the subpanel on a sturdy vertical surface in the garage, keeping it accessible and away from flammable materials or moisture-prone areas according to manufacturer and code guidance.
Strip conductors to the correct length, attach them to the main lugs on the subpanel, tighten to the manufacturer's torque settings, and verify that the grounding and bonding paths are continuous and clean.
Final Checks and Permitting
Test GFCI, AFCI, and Load Conditions
After tightening the cover, switch on the breaker at the main panel, and use a multimeter or clamp meter to check voltage at the subpanel and at receptacles.
Confirm that any required GFCI or AFCI protection devices function correctly, and run a short test with your typical tools to verify that the voltage remains stable under load.
Key Takeaways for a Safe and Code-Compliant Garage Setup
- Perform a detailed load calculation before choosing feeder wire and breaker size.
- Use proper raceway or permitted direct burial methods to route power to the garage.
- Mount the subpanel securely and verify correct polarity and grounding.
- Test GFCI and AFCI requirements as dictated by local code for garage receptacles.
- Pull permits and schedule inspections to ensure safety and legal compliance.
FAQ
Reader questions
Can I install a subpanel in my detached garage myself?
You can tackle the project if you understand local code, use the correct wire size, and feel comfortable working with main breaker panels, but hire a licensed electrician when you lack experience with feeder pulls, grounding, or permit requirements.
What wire size do I need for a 30 amp subpanel in a detached garage 70 feet away?
For a 30 amp circuit over roughly 70 feet, you will typically need 10 AWG copper conductors in a properly rated raceway or cable, considering voltage drop and local temperature conditions, and you should confirm this with a licensed pro and your local code.
Do the garage outlets need GFCI protection if they are on a 20 amp circuit?
Yes, most locations in a detached garage require GFCI protection for general-purpose outlets, often achievable with a GFCI breaker at the subpanel or a receptacle-style GFCI, and you must follow local code amendments for garage specifics.
How many circuits can I safely add to a single subpanel in my garage?
The number of circuits depends on the subpanel's main breaker rating, available space in the main service panel, and the expected loads, so review the load calculation and panel capacity before adding additional branch circuits to avoid overload.