Putting an EV Charger in a Detached Garage

Find out what the existing feeder to the garage is rated for before you shop for anything. A detached garage is typically fed by a small circuit sized for lighting and a door opener — often 20 or 30 amps — and a Level 2 charger needs a dedicated circuit of its own on top of whatever else is out there. In most cases the real project is a new feeder and a small sub-panel in the garage, and the distance makes the wire, not the charger, the biggest line item. If the feeder is already generous, an adjustable charger like the ChargePoint Home Flex lets you dial the draw to fit what is actually available.

Detached-garage installs split cleanly into two very different projects, and knowing which one you have is the whole job. Either there is enough capacity already out there and you are adding a circuit, or there is not and you are running a new feeder across the yard. The second is several times the first. Everything below is about finding out which you are in.

Step one: what is actually feeding that building?

Go look. In the main panel, find the breaker labeled for the garage, shed or outbuilding and note its rating. Then look at what is in the garage: a single breaker, a small sub-panel, or just a junction box.

• A 15 or 20-amp circuit. Common, and it means no Level 2 charging. It will run a 120-volt Level 1 cord, which adds roughly 4 miles of range per hour — about 40 miles overnight. For some drivers that is genuinely enough; see can you live with only Level 1.
• A 30 or 40-amp 240-volt feeder. Now you have options. Subtract the existing garage loads, apply the 80% continuous rule to what is left, and you may land at 16 or 24 amps of charging — which is real Level 2, roughly 12 to 17 miles per hour.
• A 60-amp or larger feeder with a sub-panel. The good case. You likely have room for a full 32- or 40-amp charging circuit, and the job becomes an ordinary install inside the garage.
• Nothing, or unknown. Treat it as a new feeder project and get it looked at. Old outbuilding wiring is also where you find the hazards — no separate ground, or a shared neutral. And to answer the question people ask at this point: a generator is not a practical substitute for a feeder, for reasons we set out in can I use a generator to charge an EV.

An electrician performing the load calculation for your permit does this arithmetic formally. The point of doing it roughly yourself first is to know whether you are discussing a small job or a trench.

Why distance costs money: voltage drop

This is the part that surprises people. Over a long run, wire has to be sized not just for the current but to keep voltage drop acceptable — the NEC's informational guidance is to keep branch-circuit drop around 3%. Resistance scales with length, so a run to a detached garage can require a conductor one or two sizes larger than the same circuit would need inside the house. Work an example:

• A 40-amp circuit for a 32-amp charger, running 100 feet to the garage, is a 200-foot round trip of conductor.
• At 240 volts, a 3% budget is about 7.2 volts of allowable drop.
• The wire that would have been adequate for 40 amps over a short run often will not hold that budget at this distance, so the installer steps up a size (or two at 150 feet or more).

Bigger wire over a longer distance, plus conduit, plus trenching or an overhead span, is why detached-garage quotes land well above the typical attached-garage install cost. It is also why running one generous feeder to a sub-panel is usually smarter than running a dedicated charger circuit all that way: you pay for the long run once, and future circuits in the garage are short.

What a detached-garage install involves

• A feeder from the main panel — underground in conduit, direct-burial cable, or an overhead span, depending on the site and local rules.
• A sub-panel in the garage with its own main breaker, plus grounding at the outbuilding per code. This is the part that makes everything afterwards easy.
• A dedicated branch circuit for the charger from that sub-panel — NEC 625.40, same as anywhere. See do I need a dedicated circuit.
• A permit and an inspection. A new feeder to an outbuilding is substantial work and inspectors look closely at outbuilding grounding.
• The charger, mounted to suit how you park. Cable reach is often tighter in a detached garage — check mounting height and cable reach before you fix the location.

What to put on the end of the feeder

Published specifications from the live listings, with live prices. The column that matters in a detached garage is the adjustable range, because you often will not know your usable amperage until the load calculation is done:

#ad Prices read live from the Amazon Product API as of October 16, 2026, and they move. Specs are the manufacturer's published claims from the live listing — we have not bench-measured them. Where we have no verified price we print none rather than a number that has gone stale.