How to Run Electricity to a Detached Garage: The Complete Planning Guide

The Load-First Rule

Before discussing subpanel size, wire gauge, or run method, calculate what you will actually run in this garage. This sounds obvious. Almost nobody does it. The typical pattern is: choose a 60-amp subpanel because it sounds like plenty, install it, add an EV charger two years later, and discover the panel is full.

The Load-First Rule: Size your electrical system for what you will run at peak load in five years, not what you are running today. The incremental cost difference between a 60-amp and 100-amp subpanel is $50 to $150 in materials. The cost of retrofitting an undersized system is $800 to $2,500. Do the calculation first.

How to Calculate Your Load

List every electrical device you plan to run in the garage and find its amperage from the nameplate on the device or its manual. Then identify which devices will run simultaneously at peak use.

Peak load example for a workshop garage:

Table saw (10A at 240V) + dust collector (6A at 240V) + shop vac (9A at 120V) + lights (3A at 120V) + heater (20A at 240V) = approximately 36A at 240V peak during a winter work session. A 60-amp subpanel handles this comfortably.

Add an EV charger (40A at 240V) and the same scenario exceeds 60 amps. You need 100 amps.

The safe approach: Add up your realistic peak load, multiply by 1.25 (the 80% continuous load rule from NEC 210.19), and size the subpanel to that number or the next standard size up.

Critical First Step: Check Your Main Panel

Subpanel or Single Circuit?

The right answer depends entirely on what you need to run.

Single branch circuit (up to 20A at 120V or 30A at 240V): Appropriate only for the most minimal garage use: basic lighting and a single outlet for a small tool or battery charger. NEC 210.11(C)(4) requires at least one dedicated 20-amp 120V circuit for garage receptacles in any powered detached garage. A single circuit cannot power multiple 240V tools or an EV charger. If you need more than one circuit, you need a subpanel.

Subpanel (60A, 100A, or larger): The right choice for any garage used as a workspace, for EV charging, or for any heating or cooling. A subpanel gives you a distribution point for multiple circuits in the garage, a local disconnect (required by NEC 225.31 for detached structures), and the capacity to add circuits later without re-running the feeder.

60-amp vs 100-amp subpanel:

The recommendation is always 100-amp. The material cost difference is $50 to $150. The labor cost is identical. A 100-amp subpanel with a 24-space panel gives you room for every circuit you need now and for the next 20 years.

Underground vs Overhead: Which Run Method Is Right?

This is the decision most homeowners agonize over unnecessarily. The right answer is usually underground, and here is why.

Underground Run

How it works: A trench is dug from the main panel to the garage. PVC conduit is laid in the trench and wire is pulled through it. The trench is backfilled.

NEC depth requirements:

• PVC conduit: 18 inches minimum depth
• Direct-burial cable (UF-B, without conduit): 24 inches minimum depth
• Under a driveway or vehicle path: 24 inches minimum for conduit, deeper is better

Advantages:

• No visible wires above ground
• Protected from storm damage and wind
• No height clearance concerns near structures or trees
• Required by many municipalities (overhead not permitted in residential areas in many jurisdictions)
• Easier to add low-voltage lines (ethernet, security camera) in the same trench

Disadvantages:

• Higher upfront cost due to trenching ($5 to $12 per linear foot for trenching labor)
• Harder to repair if a problem develops underground
• Must call 811 (Dig Safe) before digging. Hitting a utility line is dangerous and expensive

Total underground run cost (professional, 60-foot run, 100-amp subpanel): $1,500 to $3,000

Overhead Run

How it works: Wire is run overhead on a mast from the house to the garage, either on a weatherhead or strapped to a messenger cable between structures.

NEC clearance requirements:

• Above driveways and areas accessible to vehicles: 12 feet minimum
• Above pedestrian walkways: 10 feet minimum
• Above the roof of the garage: 3 feet minimum clearance from the roof surface

Advantages:

• Less expensive upfront (no trenching)
• Easier to inspect and repair
• Faster installation

Disadvantages:

• Visible wires affect curb appeal
• Vulnerable to storm damage, ice loading, and falling branches
• Clearance requirements can be difficult to meet over driveways
• Many municipalities prohibit overhead runs in residential areas. Check local codes before planning

Total overhead run cost (professional, 60-foot span, 100-amp subpanel): $800 to $2,000

The practical recommendation: Go underground. The incremental cost over overhead is typically $300 to $600 for a standard residential run. The permanence, appearance, and code compliance advantages are worth it on any property you plan to own for more than a few years.

Wire Gauge and Voltage Drop

The longer the run from your main panel to the garage subpanel, the more important wire gauge becomes. Undersized wire causes voltage drop. The actual voltage at the garage is lower than at the main panel, which causes tool motors to run hot, trip breakers, and wear out faster.

NEC standard: Keep voltage drop below 3 percent on the feeder run.

Aluminum wire consideration: For runs over 100 feet, aluminum feeder wire is a legitimate cost-saving option. Modern aluminum conductors (THHN/THWN-2 rated) are code-compliant for feeder runs when properly sized (one gauge larger than copper equivalent) and terminated correctly. Aluminum feeder for a 100-amp subpanel typically runs #2/0 AWG. The material cost savings over copper on a long run can be $200 to $400. Aluminum is not appropriate for branch circuit wiring inside the garage.

NEC Requirements for Detached Garage Electrical

These are the key National Electrical Code requirements that apply to any powered detached garage. Your local jurisdiction may have additional requirements or amendments.

Disconnect (NEC 225.31): Every detached structure supplied with electricity must have a disconnecting means at a readily accessible location either outside or immediately inside the building. If you install a subpanel with a main breaker, the main breaker serves as the disconnect.

Grounding electrode system (NEC 250.32): Any detached structure supplied by a feeder (more than a single 20-amp branch circuit) must have its own grounding electrode system, typically two ground rods driven into the earth at least 6 feet apart, connected to the subpanel's ground bus with #6 bare copper wire. Do not bond the neutral and ground bus bars in the subpanel (they are bonded only at the main service panel).

Four-wire feeder: The feeder run from the main panel to the garage subpanel must be four conductors: two hot wires, one neutral, and one ground. The neutral and ground must remain separate in the subpanel. Three-wire feeders (without a separate ground conductor) are not permitted for new installations under the current NEC.

GFCI protection (NEC 210.8): All 125V through 250V receptacles in a garage must be GFCI protected. This applies to every outlet, not just those near water sources.

Dedicated garage circuit (NEC 210.11(C)(4)): At least one dedicated 20-amp 120V circuit must supply the garage receptacles. This circuit cannot supply other outlets (with the exception of readily accessible outdoor outlets).

Lighting circuit: At least one wall-switched lighting outlet is required (NEC 210.70). It is best practice to put lighting on a separate circuit from receptacles so that a tripped breaker on the tool circuit does not leave you in the dark.

What Requires a Licensed Electrician vs. What You Can Do Yourself

This is the most practically useful section in the guide, and it is the section most articles either skip entirely or get wrong by being too restrictive in one direction or too permissive in the other.

Always requires a licensed electrician:

• Connecting the feeder to your main panel (working in the main panel with live conductors is dangerous and typically requires a permit pulled by a licensed electrician)
• Connecting the feeder to the subpanel main lugs
• Any work on the utility meter or service entrance equipment
• Final inspection sign-off in jurisdictions that require licensed work

A competent homeowner can typically do:

• Digging the trench (or hiring a landscaper to do it)
• Laying and gluing PVC conduit in the trench
• Pulling wire through the conduit
• Mounting the subpanel box on the wall
• Running branch circuit wiring inside the garage (after the subpanel is energized by the electrician)
• Installing outlets, switches, and light fixtures

The smart approach: Pull the permit yourself (or have the electrician pull it). Do the trench, conduit, and wire pull. Have the electrician make the connections at both ends, inspect your work, and sign off. This hybrid approach can save $400 to $800 in labor while keeping the dangerous work in professional hands.

Always pull a permit. An unpermitted electrical installation in a detached structure is a liability when you sell the property, may void your homeowner's insurance for any fire or damage related to the electrical system, and requires a retroactive permit (which may require tearing out and redoing work) if discovered during a future inspection. The permit fee is $50 to $200. It is not optional.

What a Complete Installation Includes

A properly completed detached garage electrical installation includes all of the following:

At the main panel:

• New double-pole breaker sized for the subpanel (60A or 100A)
• Four-wire feeder conductors connected to the breaker

The feeder run:

• PVC conduit (schedule 40 minimum) buried at 18-inch depth
• Four-wire feeder (two hots, neutral, ground) pulled through conduit
• Weatherproof conduit fittings where conduit enters both structures

At the garage subpanel:

• Subpanel with main breaker (the main breaker serves as the building disconnect)
• Neutral and ground bus bars kept separate (not bonded)
• Two ground rods driven 6 feet apart outside the garage, connected to ground bus
• All circuits properly labeled

Minimum garage circuits (for a workshop setup):

• One dedicated 20A 120V circuit for receptacles (required by NEC)
• One 20A 120V circuit for lighting (separate from receptacles)
• One or two 20A 240V circuits for stationary tools
• One dedicated 240V circuit for EV charger if planned (40A or 50A)
• One 240V circuit for heater if planned (20A to 30A)

What It All Costs

Permit cost: $50 to $200 depending on jurisdiction

Ground rods and wire: $40 to $80 (two 8-foot copper-clad rods plus #6 wire)

Trenching (if hiring out): $5 to $12 per linear foot

Seasonal Considerations

Summer: If you plan to cool the garage with a window AC or mini-split, include that circuit in your load calculation before sizing the subpanel. A mini-split requires a dedicated 240V circuit (15A to 20A). Sizing the subpanel without accounting for cooling is one of the most common garage electrical planning mistakes in warm climates.

Winter: A garage heater is a continuous 240V load, the most demanding type. A 5,000W electric heater draws 20A continuously. Add that to your peak workshop load to confirm your subpanel can handle both simultaneously. If heating is a priority, the 100-amp subpanel is even more essential. See our best garage heaters guide for circuit requirements by heater type.

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