EV Charger in a Detached Garage: What It Takes

A detached garage is one of the most common EV charging situations and one of the most commonly underestimated. The charger itself is straightforward; the work is getting power across the yard to a structure that the code treats as a separate building.

Why is a subpanel usually the right call?

You can run a single branch circuit from the house panel to a charger in the garage. But in most cases a feeder to a subpanel is the better project:

• The garage almost certainly wants lighting, receptacles and a door opener anyway
• One trench, one feeder, done — every future circuit is a short run inside the garage
• A second EV charger later is a breaker away instead of a second trench
• The disconnecting means required for a separate structure is built into the panel

The incremental cost over a single circuit is modest compared to the cost of trenching twice. See EV charger subpanel for the general case.

Sizing the feeder

Two calculations govern:

Ampacity. The feeder must carry the calculated load of everything in the garage. An EV charger is a continuous load, counted at 125% — a 48A charger contributes 60A. Add lighting, receptacles, and whatever else lives out there.

Voltage drop. This is where detached garages differ from indoor installs. Over a long run, conductor resistance causes a voltage drop that both wastes energy and can cause equipment to misbehave. The NEC's voltage-drop guidance is informational rather than mandatory in most contexts, but it's real engineering — and a charger at the end of an undersized long run is a genuine problem.

The practical effect: a feeder sized correctly for ampacity may still need to be larger because of distance. Your electrician runs the numbers for your actual length. Ballpark the load side with the home electrical load calculator and see wire and breaker size reference for the ampacity relationships.

Separate-structure requirements

The NEC treats a detached garage as a separate building, which brings requirements a same-building circuit doesn't have:

Grounding electrode system. A separate building supplied by a feeder generally needs its own grounding electrode — typically ground rods — bonded to the subpanel's equipment ground.

No neutral-ground bond at the subpanel. The neutral and equipment grounding conductors must be kept separate in the garage subpanel; they're bonded only at the service. This is the single most common DIY mistake on detached-structure subpanels.

Four-wire feeder. For a 240V feeder with neutral loads, that means two ungrounded conductors, a neutral, and an equipment grounding conductor run with the feeder.

Disconnecting means. A separate structure needs a means to disconnect all ungrounded conductors, located per the code.

Details vary by adopted NEC edition and AHJ interpretation. This is not a DIY area — hire a licensed electrician and let them pull the permit. what to ask your electrician covers what to ask.

Getting the feeder there

Underground is the usual route. That means:

• Calling 811 for utility locates before digging — free, and non-negotiable
• Trenching to the minimum cover depth required for your wiring method (the NEC has a table; depth depends on the method and what's above)
• A wiring method suitable for the environment — direct-burial cable or conductors in raceway, per your electrician's design
• Warning tape or other identification where required

Overhead is possible where an existing span or structure supports it, with its own clearance requirements — but it's less common for new work.

Trenching cost is driven by length and by what's in the way. Crossing a lawn is cheap; crossing a concrete driveway means saw-cutting and patching, and that patch is often the single largest line item. Some installers can bore under a driveway instead, which is worth asking about.

EV charger conduit and wire runs covers routing generally, and outdoor EV charger installation covers the weather side.

Does your service have room?

Adding a garage feeder means adding its calculated load to your service. Before designing anything, run a load calculation.

Load management is especially useful here, because it can cap the charger's contribution to the calculation and let a modest feeder serve the garage. See EV charger load management and panel upgrades for EV charging.

Inside the garage

Once the feeder lands:

• Mount the charger where the cable reaches the port in your normal parking position, in both directions if you sometimes back in
• Protect it from vehicle impact if it's at the end of a bay — inspectors often want a bollard where contact is plausible
• Match the enclosure rating to the garage environment; an unheated detached garage sees the full temperature swing, so check the unit's minimum operating temperature
• Add lighting and receptacles on separate circuits while the panel is going in — it costs almost nothing now

Cable reach in a two-bay detached garage is a real constraint. Measure the routed path around the vehicle, not the straight line — EV charger cable length.

What does an EV charger in a detached garage cost?

The charger is a small share. The cost drivers, roughly in order:

1. Trench length, and whether it crosses hardscape
2. Conductor size — driven by load and by voltage drop over distance
3. Subpanel and grounding electrode work
4. Restoring driveway, walkway or landscaping
5. Panel work at the house end, if the main is full

Estimate with the home charger install cost calculator, and read EV charger installation cost for what moves the number in general.

The bottom line

A detached garage EV charger is really a feeder-and-subpanel project with a charger at the end. Size the feeder for both ampacity and voltage drop over the actual distance, plan for the separate-structure grounding and disconnect requirements, call 811 before digging, and put in a subpanel so the trench only ever gets dug once. Then the charger install is the easy part.

Check capacity with the home electrical load calculator, estimate the job with the home charger install cost calculator, or see wire and breaker sizes.