What a Subpanel Actually Is
A subpanel is a smaller electrical panel that connects to your main service panel through a feeder circuit. Think of your main panel as the trunk of a tree; the subpanel is a major branch that splits power off to serve a specific area.
Like your main panel, a subpanel contains breakers that control individual circuits. The key difference: the main panel connects directly to your utility meter and has a main disconnect breaker. A subpanel receives power from the main panel and doesn't have a main disconnect — it's protected by a breaker in the main panel.
Subpanels typically range from 60A to 100A capacity, fed by 6 AWG or larger copper wire (or equivalent aluminum). The feeder circuit includes two hot conductors, a neutral, and a separate ground. In subpanels installed after the 2008 NEC, grounds and neutrals must be on separate bus bars — bonding them together like in a main panel creates a dangerous ground loop.
A properly installed subpanel extends your electrical system's reach without overloading the main panel or running individual circuits across long distances, which would cause voltage drop and code violations.
When You Need a Subpanel Instead of More Main Panel Circuits
You're considering a subpanel if any of these apply:
- Your main panel is full. No empty breaker slots, and tandem breakers won't help or aren't allowed for your panel type.
- You're building or finishing a detached garage, workshop, or pool house. Running 8–10 individual circuits from the main panel across your yard is expensive and impractical. One subpanel feeder run is cleaner.
- You're adding a home addition or converting a basement. The new space needs multiple circuits for outlets, lighting, HVAC, and appliances. A subpanel keeps all those breakers organized in the new space instead of scattered in a distant main panel.
- You're installing high-draw equipment far from the main panel. A woodshop with table saws and dust collectors, a home gym with multiple outlets, or an RV hookup with a 50A receptacle all benefit from a local subpanel.
- You want dedicated circuits for sensitive equipment. Audio/video systems, server racks, or medical equipment sometimes need isolated branch circuits — a subpanel simplifies this.
If you're just adding 2–3 circuits and your main panel has space, you probably don't need a subpanel. If you're adding 6+ circuits or running power more than 75 feet, a subpanel is usually the right call. An electrician will calculate wire gauge for the feeder to avoid voltage drop over the distance — typically 3% maximum under NEC guidelines.
How Subpanel Installation Works (and Why It's Not DIY)
Installing a subpanel means working inside the main panel — feeding the new feeder circuit through a large breaker (often 60A, 80A, or 100A depending on the subpanel rating). That's live work. The main panel remains energized even when you shut off branch breakers, because the main breaker itself is downstream of the utility connection. Only the utility or a licensed electrician should work on those connections.
The subpanel itself mounts in the new space — garage wall, basement, workshop. The electrician will:
- Calculate feeder wire size based on subpanel amperage and distance from the main panel
- Run the feeder circuit in conduit (often required for outdoor or exposed runs) or appropriate cable
- Install a breaker in the main panel sized to the feeder wire and subpanel rating
- Wire the subpanel with separated ground and neutral buses (critical for safety)
- Install breakers in the subpanel for the new branch circuits
- Run branch circuits from the subpanel to outlets, lights, and equipment in the new space
- Test and label everything, pull permits, and schedule inspection
Permits are required for subpanel installation in South Florida. Inspection verifies proper wire sizing, bonding, grounding, and clearances. If you skip this and sell your home, the buyer's inspector will flag it — or worse, an electrical fire could trace back to improper installation.
For a full range of electrical upgrades and panel services, working with a licensed contractor ensures code compliance and safety.
Subpanel Capacity: Matching Load to Wire Size
A 60A subpanel doesn't mean you can use all 60 amps continuously. Electricians calculate the actual connected load — all the circuits you'll run from the subpanel — and size the feeder accordingly. If you're powering a garage with LED lighting, a garage door opener, a couple of 20A tool circuits, and a 240V welder outlet, the calculated load might be 40A. A 60A subpanel with 6 AWG copper feeder gives you headroom.
If you're running a detached shop with a dust collector (240V, 20A), multiple saws, HVAC, and a full complement of outlets, you might need a 100A subpanel with 2 AWG aluminum or 3 AWG copper, depending on distance. Wire costs jump significantly at larger gauges, so right-sizing matters.
Voltage drop is the limiting factor on long runs. South Florida code generally requires voltage drop under 3% for branch circuits and 5% total. A 100A feeder run 150 feet in 2 AWG aluminum will have different drop characteristics than the same run in copper. Your electrician will calculate this using NEC Chapter 9 tables or voltage drop formulas, then upsize wire if needed.
Never assume you can use the maximum breaker rating continuously. Electric vehicle charging, for example, should run at 80% of breaker rating for safety. A 50A circuit should carry no more than 40A continuous load. The same principle applies to subpanel feeders — continuous loads factor into sizing.
Grounding and Bonding in a Subpanel: The Critical Difference
This is where most DIY subpanel installs go dangerously wrong. In your main service panel, the neutral bus and ground bus are bonded together — they're electrically connected, often with a green screw or bonding strap. That bond happens once, at the service entrance, where the grounded (neutral) conductor connects to the grounding electrode system (ground rods, Ufer ground, water pipe bond).
In a subpanel, grounds and neutrals must be separated. The subpanel should have two bus bars: one for neutrals (white wires from branch circuits and the white feeder wire from the main panel) and one for grounds (bare copper or green wires from branch circuits and the ground feeder wire). If you bond them together in the subpanel, you create a parallel path for neutral current to flow on the ground wire back to the main panel. That's a code violation and a shock hazard.
The four-wire feeder (two hots, one neutral, one ground) keeps these paths separate. Older installations sometimes used three-wire feeders (two hots and a neutral that also served as ground), but that's no longer code-compliant for new work. If you're replacing an old subpanel or adding a new one, you need that fourth wire.
Inspectors check this. If the neutral-ground bond is wrong, you'll fail inspection. More importantly, if someone touches grounded metal (a tool, a metal junction box, a garage door frame) while standing on concrete or wet ground and there's a ground fault, improper bonding can mean the difference between a tripped breaker and electrocution.
Cost Factors and Planning Your Subpanel Project
Subpanel installation costs vary widely based on:
- Feeder distance. A subpanel 20 feet from your main panel is cheaper than one 150 feet away in a detached structure. Wire cost scales with distance and gauge.
- Subpanel amperage. A 60A panel with 12 circuit slots costs less than a 100A panel with 24 slots. Match capacity to actual need plus 25% future expansion.
- Conduit requirements. Outdoor runs, exposed wiring, or underground trenching add labor and material cost. PVC conduit is cheaper than rigid metal, but code dictates what's required in each application.
- Permit and inspection fees. These are unavoidable and worth every dollar. Municipalities in South Florida charge $100–300 depending on project scope.
- Branch circuit work. Just installing the subpanel is step one. Running new circuits from it to outlets, lights, and equipment is additional labor. Get a complete quote that includes both.
Typical residential subpanel projects range from $1,200 for a simple 60A garage panel with short feeder run and 4–6 new circuits, up to $4,000+ for a 100A detached workshop with long underground feeder, full breaker loadout, and extensive branch circuits. Commercial work costs more due to larger panels, heavier feeders, and stricter code requirements.
Plan the project when the space is framed but not finished. Running wire before drywall goes up is faster and cheaper. If you're retrofitting an existing finished space, expect more labor for fishing wire and patching walls. For questions about your specific project, check our electrical blog for related topics or reach out directly.
When to Call for Subpanel Installation
If you're planning a garage conversion, workshop build-out, pool house, or major addition and the words "I need more circuits" come up, start the conversation with a licensed electrician early. They'll visit the site, look at your main panel capacity, measure distances, discuss your actual loads (tools, HVAC, EV charger, etc.), and provide a detailed quote before any work starts.
Subpanel work isn't an emergency repair (unless the existing subpanel has damage or safety issues), but it's not a weekend DIY project either. Between pulling permits, calculating loads, sizing wire, working in the main panel, and scheduling inspection, this is squarely in professional territory. The upside: done right, a subpanel is a permanent upgrade that adds real value and convenience to your property.
If your project involves upgrading the main panel first — say, going from 100A to 200A service to handle the new subpanel load — that's a separate scope but often combined into one project. The electrician will coordinate with the utility for meter disconnect if required. Either way, the process starts with an honest assessment of your current system and your future needs.
Need help planning a subpanel installation or evaluating your main panel capacity? Call (954) 602-0050 anytime. We provide up-front pricing quoted before any work starts, and our licensed electricians serve residential and commercial properties across South Florida. Whether it's a scheduled upgrade or an unexpected panel issue, we come to you — day or night. For more about our electrical services or to reach us directly, visit our contact page.