How to Install a Garage Subpanel

Subpanels are the most effective way to manage heavy electrical loads in a detached workspace or garage without constantly tripping main house breakers. By bringing a dedicated feed to the garage, you gain the ability to run welders, air compressors, and heavy lighting simultaneously, effectively turning a simple storage area into a functional workshop. A job done well results in a clean, code-compliant install where every circuit is clearly labeled and perfectly balanced. Safety is the primary currency here. You are working with high-amperage lines that carry significant danger; if you have any doubt about wire sizing or panel grounding requirements, step back. This process requires a permit in nearly every jurisdiction, and for good reason. When executed correctly, the subpanel becomes the heart of your garage electrical system, providing reliable, isolated power that respects the integrity of your home's primary electrical service.

  1. Size Your Feeder First. Calculate your total garage amperage requirements and select the appropriate gauge wire for your feeder circuit. Use copper THHN wire inside conduit or appropriately rated NM-B cable based on your local code requirements for the run distance.
  2. Mount Perfectly Vertical. Secure the subpanel housing to a stud or plywood backer board at eye level. Ensure the cabinet is level and plumb, allowing enough clearance for conduit entries from the top or bottom.
  3. Route With Care. Route the feeder cable from the main service panel to the subpanel location using appropriate conduit or cable staples. Secure the cable every 4.5 feet and within 12 inches of entering each panel.
  4. Isolate Neutral and Ground. Install a separate ground bar in the subpanel and ensure the neutral bar is isolated from the cabinet chassis. Do not bond the neutral to the ground in a subpanel; this is only done at the main service panel.
  5. Kill Power. Connect Breaker.. Install a double-pole breaker in the main service panel to feed the subpanel. Connect the hot wires to the breaker, and the neutral and ground wires to their respective bars in the main panel.
  6. Test, Torque, and Label. Check all terminal torques with a screwdriver, verify voltage levels with a multimeter, and install the front cover. Label every individual circuit on the subpanel directory for future reference.