A sub panel — also called a secondary panel or load center — is a smaller electrical panel that receives power from your main panel and distributes it to a specific area of your home, such as a detached garage, an accessory dwelling unit, a workshop, or a finished basement. It functions just like the main panel but is subordinate to it, taking a portion of the home’s total electrical capacity and managing it locally.

Why Sub Panels Are Installed

The most common reason to install a sub panel is distance. Running individual circuits from a main panel to a detached garage 100 feet away, for example, would require multiple long home runs of heavy wire — expensive and impractical. A sub panel solves this by running a single large feeder cable from the main panel to the sub panel, then distributing multiple circuits locally from the sub panel at the destination. It’s more efficient and gives you more flexibility in what you can power in that space.

Sub panels are also installed inside the main house when the main panel is full and can’t accommodate additional circuits — a common situation in older Denver-area homes that were originally wired for 100-amp service and have since had significant electrical additions.

How a Sub Panel Is Wired

A sub panel is fed by a dedicated two-pole breaker in the main panel sized to match the sub panel’s capacity — commonly 60, 100, or 125 amps. The feeder runs from that breaker to the sub panel via a four-wire cable or conduit (two hot conductors, a neutral, and a separate ground). At the sub panel, the neutral and ground bus bars must be kept separate — a critical difference from the main panel, where they are bonded together. Failure to separate them at a sub panel creates a shock hazard and a code violation.

From the sub panel, individual circuits are run to outlets, lighting, and equipment in the served space, just as they would be from the main panel.

Common Applications on the Front Range

In Colorado, sub panel installations frequently come up in these scenarios:

  • Detached garages being converted to workshops or hobby spaces with 240V equipment
  • Accessory dwelling units (ADUs) — increasingly common in Denver and surrounding municipalities — that need separate metering or substantial electrical capacity
  • Finished basements with home theaters, wet bars, or home gyms requiring multiple dedicated circuits
  • Home additions where the main panel is already at capacity
  • Barns or outbuildings on larger Front Range properties

Sub Panel vs. Main Panel Upgrade

If your main panel is full, you have two options: upgrade to a larger main panel with more breaker slots, or install a sub panel fed from your existing main panel. A sub panel is generally the less expensive option in the short term, but it only works if your main panel has enough capacity to feed the sub panel without overloading the overall service. If your home is already at 100-amp service and you’re adding significant loads, a service upgrade to 200 amps may need to happen alongside or instead of a sub panel.

An experienced electrician will assess both your main panel’s available capacity and your service entrance before recommending a path. Adding a sub panel to a service that’s already strained doesn’t solve the underlying problem.

Permits and Inspections

Sub panel installation is permitted work in Colorado. The permit, installation, and inspection process is the same as for any panel work — a licensed electrician pulls the permit, the local jurisdiction inspects the completed work, and the inspection record becomes part of your home’s permit history. This matters at resale: unpermitted electrical work, including sub panels, can complicate transactions and may require remediation.

Done’s electricians handle sub panel installations throughout the Denver metro and Front Range. Visit our panels and wiring page to get started, or explore our electrical installations and remodels services if your sub panel project is part of a larger renovation.