Sub-Panel Installation for Garage and Detached Charging

A single 240-volt branch circuit run straight to the charger is the cheapest way to charge a car in a garage or a workshop, and it is a perfectly legal way to do it. It does exactly one job. If lighting and a receptacle or two are already there and working, and nothing about the space is changing, a home-run circuit for the charger alone is a reasonable answer.A subpanel earns its cost the moment there is a second thing to feed: lighting that is not there yet, a couple of general-purpose receptacles, a compressor or a bench tool, a second EV in the household eventually. Instead of pulling a second wire back to the house for every one of those, the subpanel gives the building its own small set of breakers and the house only sees one feeder.If the building sits away from the house, this decision also runs into the code's general rule that a separate structure is normally supplied by one feeder or one branch circuit — not one of each, and not several of either without upgrading the supply. That trench-and-feeder side of the question, including burial depth and the route across the yard, is covered on its own page; this one is about what happens at the panel end.

A 48-amp charger alone needs a 60-amp two-pole breaker and nothing else. A subpanel sized to exactly that gives you the charger and almost no room for anything else, which is the mistake people make when they size the panel to today's plan instead of the building's life. Spaces are cheap when the panel is a line item on the invoice already; they are not cheap once the cover is back on and inspected.How much headroom the subpanel can actually be given is set upstream, by how much spare capacity your main panel has to spend on a new feeder — which is its own calculation, not a guess at the truck. If you are not sure your main panel has room for any of this, start with the load calculation question before you pick a subpanel size.

A main-lug-only subpanel has no overcurrent device of its own at the top — the feeder breaker back in the main panel is what protects it and what you'd shut off to work on it. That is fine for a subpanel inside the same building as the main panel, where nobody needs to find a disconnect standing at the detached structure itself.A main-breaker subpanel has its own switch at the top, sized to the feeder, and it can be opened without walking back to the house. For a subpanel that also has to satisfy the separate-structure disconnect requirement — because the garage, workshop or outbuilding is not part of the same building as the house — the main breaker is usually what does that job, rather than adding a second disconnect device beside it.Cost difference between the two is modest; a main breaker is a few hundred dollars of hardware. The decision that actually matters is the one below.

An attached garage or workshop — sharing a wall or a roofline with the house, not a separate footprint — is generally treated as part of the same building for this purpose. Its subpanel is an ordinary interior subpanel: no separate-structure disconnect requirement, no separate grounding electrode system, because it never left the building the service already grounds.Step the same panel into a detached structure and two requirements attach that were not there a moment ago. Article 225 calls for a disconnecting means at the structure — satisfied by a main-breaker subpanel — and 250.32 calls for a grounding electrode system at the structure itself, typically a pair of ground rods, because the building is no longer relying on the house's grounding alone. The feeder also has to be four-wire, with the neutral and the equipment ground kept separate at the subpanel rather than bonded there.None of that is a reason to avoid a detached subpanel. It is a reason the same-looking panel costs more once it crosses the yard, and a reason to ask which side of that line your building sits on before you compare two quotes that scoped it differently.

The EV charger circuit is sized the way it always is: continuous load, breaker and conductors at 125 percent of the charger's maximum current. Stationary shop equipment with a motor — a compressor, a table saw, a dust collector, a welder — follows a different rule under Article 430, where the feeder supplying more than one motor is sized for the largest motor's full-load current at 125 percent plus the full-load current of the rest. Mixing those two kinds of load on one feeder is normal; sizing them by the same shortcut is not.There is also a real difference in how the building's general lighting and receptacle load gets counted once the structure is detached and not itself a dwelling unit. A house uses the optional dwelling-unit method for that; a stand-alone garage or workshop that is not a dwelling is calculated under the code's general method by occupancy type, which is a separate table and a separate conversation with whoever is running the numbers. Ask which method they used, the same way you would for the house's own load calculation.The practical upshot: tell the electrician everything that will ever plug into or hard-wire to that subpanel, not just the charger, before the feeder size gets picked. A welder added after the trench is closed is the same expensive mistake as a second charger added after a single circuit was run.

Most jurisdictions cover the subpanel and the charger circuit on one permit, but the inspector is looking at more than the breaker the charger lands on. A few things specific to the panel itself: the directory inside the door has to legibly identify what each breaker feeds, which matters more here than in a house panel because a garage or workshop subpanel tends to get added to for years after the original install. The panel's own listing label governs what can go in it — the same rule that decides whether tandem breakers are allowed anywhere in a full main panel applies here too. And if the structure is detached, the grounding electrode and the disconnect are their own inspection items, generally checked before the trench gets closed.Ask for the subpanel to appear on the permit as its own scoped item — amperage, main lug or main breaker, spaces, and the grounding work if it's detached — rather than folded into a single line that just says "EV charger circuit." A quote that only mentions the charger has not scoped the panel.

There is no separate national figure for "subpanel installation" as its own line item, because the two scenarios below cost differently for different reasons and averaging them would hide both. Both bands are the site's already-published modelled ranges, sourced the same way as the rest of this site's cost figures, not a new number invented for this page.