Subpanels act as secondary electrical distribution points that extend power to specific areas of your home or garage without overloading your main panel. If you're renovating, adding a workshop, or installing heavy equipment like an EV charger, a subpanel may be the most practical solution your electrician recommends. Understanding when you need one—and what installation actually involves—helps you make informed decisions and budget correctly.
What a Subpanel Does
A subpanel receives power from your main electrical panel and redistributes it to circuits in a remote location. Instead of running individual wires from your main panel 100+ feet to a garage or basement workshop, you install a subpanel closer to where you need the power. This reduces wire runs, minimizes voltage drop, and keeps your main panel from becoming overcrowded with new breakers.
Subpanels typically range from 100 amps to 200 amps in capacity, though you'll usually install one that matches your actual power needs rather than maxing out the size.
When You Actually Need One
Not every electrical upgrade requires a subpanel. Your electrician will recommend one under these specific conditions:
- Adding 40+ amps of new circuits (like a 240V EV charger, hot tub, or detached garage with multiple tools)
- Distance exceeds 75 feet from the main panel to where power is needed
- Main panel has no available breaker slots left for new circuits
- New equipment requires dedicated circuits at a location far from the main service
If you only need to add one 20-amp circuit for a bedroom outlet, your electrician will likely just extend from the main panel. A subpanel becomes cost-effective when you're consolidating multiple new circuits in one location.
What Installation Typically Involves
The process breaks down into distinct phases:
Permit and Inspection Your electrician must pull a permit before work begins—this isn't optional. Most jurisdictions require inspections at rough-in stage (wiring done, before closing walls) and final sign-off. Permits cost $75–$200 depending on your area and typically take 1–3 weeks to process.
Main Panel Assessment The electrician checks your main panel's available breaker slots and existing load. If your home already runs near capacity, you may need to upgrade your main service (200 amps) before adding a subpanel—a significantly larger job ($3,000–$5,000). If capacity exists, they size the subpanel and plan the feeder cable run.
Feeder Cable Installation A large cable (often 2/0 or 3/0 copper) runs from a breaker in your main panel to the subpanel location. This cable must be protected—either run through conduit, buried at least 18 inches underground (if outside), or placed inside walls during renovation. Cable runs of 75–150 feet are routine; longer distances require larger wire gauges to prevent voltage drop.
Subpanel Mounting and Connection The subpanel is mounted (typically on a wall in the target area—garage, basement, or exterior wall), grounded properly with a ground rod if it's in a detached building, and the feeder cable is connected to a breaker and bus inside the panel.
Branch Circuit Wiring Once the subpanel is live, individual circuits for lights, outlets, equipment, and hardwired devices are wired from the subpanel breakers.
Cost and Timeline Reality
A straightforward subpanel installation with indoor cable runs typically costs $2,500–$4,500 in labor and materials. This includes:
- Subpanel unit ($300–$800)
- Feeder cable and conduit ($500–$1,200)
- Labor ($1,500–$2,500)
- Permits and inspections ($75–$200)
Outdoor runs, longer distances, or main service upgrades push costs higher. Timeline averages 2–4 weeks from permit approval to final inspection.
If you're comparing electricians and subpanel quotes, ensure each includes a site visit, load calculation, and detailed scope. Mercoly helps you find and compare trusted panel upgrade and rewiring providers in one place, so you can review experience, pricing, and customer feedback before deciding.
Frequently Asked Questions
Q: Can I install a subpanel myself? No—electrical work requires a licensed electrician in every state, and DIY subpanel installation voids permits, insurance, and home sale disclosures. Improper installation risks fire and electrocution.
Q: Do I need a separate breaker in my main panel for the subpanel? Yes, the subpanel feeder must run through a dedicated breaker (typically 100–200 amps) in your main panel; this breaker protects the feeder cable from overload.
Q: What's the difference between a subpanel and a transfer switch? A transfer switch moves power between two sources (grid to generator); a subpanel distributes power to multiple circuits in one location. They solve different problems.
Compare quotes from licensed electricians in your area today—proper subpanel sizing and installation protects your home and your investment.