Installing an EV charger in a detached garage

A detached garage turns a straightforward job into a construction project, because the power has to physically get there. Published labor figures for this category run roughly $1,500 to $3,000 before any panel work, and the variable that dominates is whether a feed already exists.

Start here: is there already a feed?

Many detached garages already have power for lights and outlets. Go and look at what is there:

What a new feed involves

1. 1.A trench from the house to the garage, at a code-specified depth that depends on the wiring method and whether it is under a driveway.
2. 2.Conductors rated for wet locations, sized for both the load and the voltage drop over the distance.
3. 3.A subpanel in the garage, with its own disconnect and grounding arrangement, since a detached structure has particular grounding requirements.
4. 4.Restoration of whatever the trench went through -- lawn, driveway, patio. This is a real cost people forget.

Voltage drop: the reason distance costs money

Over a long run, resistance in the conductors causes the voltage at the far end to sag. The standard fix is thicker conductors, and copper is priced by weight -- so a 120-foot run does not cost twice a 60-foot run, it costs more than twice, because the wire itself steps up a size or two as well.

This is why an electrician will ask the distance before quoting, and why a quote given over the phone without it is not worth much.

The alternative worth considering first

If the trench is long and the driveway is in the way, ask a genuinely useful question: does the charger have to be in the garage?

Mounting it on the house wall nearest where you park can eliminate the trench entirely. You need a weather-rated unit and a cable long enough to reach, but on a 25-foot cable with the car parked on the driveway, this frequently works -- and it can turn a $4,000 project into a $1,500 one.