Subpanels for Garages, ADUs, and Workshops

A subpanel is a smaller breaker box fed from your main service panel that gives a garage, ADU, or workshop its own breakers and its own shutoff. You need one when the structure sits far enough from the house that running individual circuits back to the main panel becomes impractical, when the total load exceeds what a single branch circuit can carry, or when local code requires a disconnecting means at the separate structure. In Upland, that usually means a detached garage, a converted ADU, or a workshop running a 240V welder or dust collector.

This guide covers how we size subpanels for each of those three cases, what installation runs in 2026, and the mistakes that turn a weekend project into a failed inspection.

What a Subpanel Actually Does

A subpanel does not create new power. It redistributes power you already have, which is why the first question on every subpanel job is whether your main service can spare the amps. A 100-amp main panel feeding a house with central air, an electric range, and a dryer has very little headroom left for a 60-amp garage feed.

What the subpanel buys you is convenience and code compliance. Instead of pulling six separate home runs 80 feet through a trench, you pull one feeder and land it on a 100-amp breaker in the sub. From there, every circuit in the garage or ADU terminates locally. If a GFCI trips while you are running a table saw, you reset it at the sub, not in the house.

It also gives you a labeled disconnect at the structure. That matters for firefighter safety and for anyone servicing equipment in a detached building. Most Upland inspectors want to see that disconnect clearly marked and accessible, not buried behind stored boxes.

If your main panel is already maxed out, adding a subpanel is the wrong first move. We run a load calculation first, and if the numbers do not work, we talk about a 100 to 200 amp service upgrade Upland CA before we touch the subpanel. That order saves homeowners from paying twice.

Do You Need a Subpanel for a Garage, ADU, or Workshop in Upland?

You need a subpanel in Upland when the structure is detached, when the total connected load exceeds 50 amps, or when you are adding 240V equipment like an EV charger, welder, or mini-split. The 2022 California Electrical Code, which Upland enforces, requires a disconnecting means at any separate structure with more than one branch circuit.

Here is the practical test we use on site:

• One circuit, lights only: no subpanel needed. A single 20-amp circuit from the house works.
• Two or more circuits, or any 240V load: subpanel required.
• Detached structure with a feeder over 50 feet: subpanel strongly recommended for voltage drop and code.
• ADU with kitchen, bath, and HVAC: 100-amp subpanel minimum, often 125 amps.

Voltage drop is the part most homeowners miss. A 120V circuit run 120 feet on 12-gauge wire loses enough voltage that a circular saw bogs down and a garage door opener runs hot. A subpanel fed with the right size aluminum or copper feeder eliminates that problem entirely.

If you are not sure which side of the line you are on, an electrical load calculation and inspection Upland CA tells you exactly what your service can support before you spend a dollar on hardware.

Sizing a Subpanel: 60, 100, or 125 Amps

Size the subpanel by the load you will actually run, then add 25 percent headroom. Undersizing is the single most common mistake we correct on subpanel jobs in Upland, and it usually shows up the first summer the homeowner adds a mini-split to the garage.

60-amp subpanel

Good for a basic detached garage with lights, outlets, and a garage door opener. It handles one 240V load up to about 30 amps. Not enough for an EV charger plus a compressor plus lighting.

100-amp subpanel

The workhorse for Upland garages and small workshops. Runs a 40-amp EV charger, a 30-amp compressor, and standard lighting without strain. This is what we install most often for a subpanel installation Upland CA on a detached garage.

125-amp subpanel

What most ADUs need. A 600-square-foot ADU with a mini-split, electric water heater, range, and laundry will pull 80 to 100 amps at peak. A 125-amp sub gives you the margin. Anything larger than 125 amps usually means stepping up the feeder wire size and re-checking the main panel.

Feeder size matters as much as the panel rating. A 100-amp subpanel needs 1/0 aluminum or 2-gauge copper for a typical 80-foot run. Undersized feeders cause nuisance trips and heat at the lugs, which is a fire risk, not a nuisance.

What Subpanel Installation Costs in Upland in 2026

Typical 2026 pricing for subpanel installation in Upland runs $1,400 to $3,200 for a detached garage and $2,800 to $6,500 for an ADU, depending on trenching, feeder length, and whether the main panel needs work. Those are installed prices, including the panel, breakers, feeder, conduit, and permit.

What drives the number up or down:

• Distance from main panel: every 10 feet of trench and conduit adds roughly $80 to $140.
• Trenching: hand-digging through Upland's decomposed granite is slow. If the run crosses a concrete patio or driveway, add $600 to $1,800 for cutting and patching.
• Main panel capacity: if your existing panel cannot spare the amps, a service upgrade adds $2,200 to $4,500.
• Permit and inspection: Upland pulls a permit for subpanel work. Budget $180 to $350 for the permit and inspection fees.
• AFCI and GFCI breakers: required for most garage and ADU circuits. Each breaker runs $45 to $75 installed.

We give you the number before we start, and it does not move unless you change the scope. If you want to know what your specific layout will cost, we will walk the property and quote it.

ADU Subpanels: What Upland Permits Require

An ADU subpanel in Upland must be sized for the ADU's full connected load, be fed from the main service with a properly sized feeder, and include a labeled main disconnect at the ADU. The city treats an ADU as a dwelling unit, so the electrical has to meet dwelling-unit code, not garage code.

That means AFCI protection on bedroom and living-area circuits, GFCI protection in the kitchen and bath, and a grounding electrode system at the ADU if it is a detached structure. We see a lot of owner-built ADUs in the San Antonio Heights and North Upland areas where the subpanel was sized for a garage and then the ADU grew a kitchen and a mini-split. The panel has to be replaced before the final inspection.

Plan for 100 to 125 amps for a one-bedroom ADU and 125 to 150 amps for a two-bedroom with laundry. If you are also adding an EV charger at the ADU, size up. We handle the load calculation, the permit paperwork, and the inspection so you are not chasing the city on your own.

Homeowners in San Antonio Heights Electrical Panel Upgrade territory deal with longer feeder runs and older main panels more often than anywhere else we work, so we usually quote the ADU subpanel and the main panel together.

Detached Garage and Workshop Subpanels

A detached garage subpanel in Upland needs a 60-amp minimum feed, a grounding electrode at the structure, and a disconnect if the garage has more than one circuit. For a workshop running a welder or a 3HP dust collector, we start at 100 amps.

Workshop loads are different from garage loads because they are intermittent and high-draw. A 240V MIG welder pulls 30 to 50 amps on its own. A cabinet saw pulls 13 to 18 amps at startup. A dust collector pulls 12 to 16 amps continuous. Add lighting and a mini-split and you are at 80 amps before you plug in a battery charger.

We size workshop subs at 100 or 125 amps and run 2-gauge copper or 1/0 aluminum feeders. If the run exceeds 100 feet, we bump the feeder one size to hold voltage under load. That is the difference between a welder that runs clean and one that trips the breaker mid-bead.

For a detached garage subpanel Upland homeowners often ask about, the trench is the wild card. We can direct-bury the feeder in Schedule 80 PVC at 18 inches, or run it in rigid conduit at 6 inches if you need to cross a driveway. We will tell you which one your yard allows.

If the garage is also going to charge an EV, plan for it now. An EV-ready and solar-ready panel upgrades Upland CA setup at the subpanel level costs a few hundred dollars more today and saves a full re-trench later.

Common Mistakes We See on Subpanel Jobs

The mistakes that fail inspection in Upland are almost always the same five, and four of them are grounding and neutral issues.

1. Bonding neutral and ground at the subpanel. The neutral bar and ground bar must be isolated in a subpanel. Bonding them creates parallel return paths and is a shock hazard. This is the number one fail.
2. No grounding electrode at a detached structure. A detached garage or ADU needs its own ground rod and grounding electrode conductor.
3. Undersized feeder. A 60-amp feeder on 6-gauge copper for a 120-foot run will not hold voltage. We see this on owner-installed jobs constantly.
4. Wrong breaker type in the main panel. The feeder breaker must match the panel brand and be listed for it. Mixing brands voids the listing.
5. No disconnect or an unlabeled one. Inspectors want a clearly marked disconnect at the structure, and so does the fire department.

One more: skipping the permit. Unpermitted subpanel work shows up in a title search when you sell, and Upland will require it to be brought to current code before the sale closes. The permit costs a few hundred dollars. The retrofit costs thousands.

When to Call a Professional

Call a licensed electrician when the subpanel feeds a detached structure, when the main panel needs a load calculation, or when any part of the run involves trenching, conduit bending, or a service upgrade. Those are the jobs where a mistake is not a callback, it is a fire.

We handle subpanel work across Upland every week. Our electricians pull the permit, run the load calculation, trench and set the feeder, install the panel and breakers, and meet the inspector on site. You get a labeled panel, a passed inspection, and a walkthrough of what every breaker controls before we leave.

If your project also involves replacing an aging main panel, we can bundle it. Homeowners in The Colonies Electrical Panel Upgrade area often pair a garage subpanel with a main panel replacement because the original 100-amp panel cannot carry both the house and the new load.

We are a local electrical panel upgrade company serving Upland and the surrounding foothill communities. If you want a straight answer on whether your project needs a subpanel, a service upgrade, or both, call us and we will tell you.

Frequently Asked Questions

Do I need a subpanel for my garage in Upland CA?

You need one if the garage is detached and has more than one circuit, or if you are adding any 240V load like an EV charger or welder. A single 20-amp lighting circuit on an attached garage does not require a subpanel.

How much does ADU subpanel installation cost in Upland, California?

Expect $2,800 to $6,500 in 2026, including the panel, feeder, trenching, breakers, and permit. Long runs, concrete cutting, and a main panel upgrade push the number toward the top of that range.

Can I install a subpanel in my workshop in Upland CA?

Yes, and a workshop subpanel is usually the right call. Size it at 100 to 125 amps if you run a welder, dust collector, or large compressor. The work needs a permit and a load calculation on the main panel first.

What size subpanel do I need for an ADU in Upland CA?

A one-bedroom ADU needs 100 amps. A two-bedroom with laundry and a mini-split needs 125 amps, and 150 amps if you are adding an EV charger. Size by connected load, not by square footage.

How long does subpanel installation take?

A detached garage subpanel takes one to two days. An ADU subpanel with trenching takes three to five days, plus one to two weeks for the permit and inspection. We schedule the inspection before we start.

Get Help With Electrical Panel Upgrade in Upland

Whether you need a garage subpanel, an ADU subpanel, or a full service upgrade to support one, we will size it right the first time and get it inspected. Call Upland Electrical Panel Upgrade at (909) 850-3163 for a same-week estimate.