How to Install an Electrical Subpanel

We make it easy for you to add circuits with our step-by-step guide to installing an electrical subpanel.
By BH&G Editors Updated January 15, 2021
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If your home's service panel doesn't have room for new circuit breakers and you cannot use tandem breakers, a subpanel might be the answer. A subpanel connects to the main service panel with a thick three-wire cable. The feeder breaker in the main panel acts as the main disconnect for the subpanel. Before installing a subpanel, consult with an inspector to make sure you do not overload your overall system.

A subpanel has separate bus bars for neutral and ground wires and typically has no main breaker. It may not be labeled "subpanel." Instead, it might be labeled "lugs only." Additionally, it might be a different brand than the main panel. Have the inspector approve the subpanel, the feeder cable, and the feeder breaker before you start installing a subpanel.

Safety is most important when installing anything with wires or electrical work. When dealing with electrical projects, shut off the power first. Before you begin installing a subpanel, shut off the main breaker in the service panel.

  • Start to finish 2 hrs
  • Difficulty Kind of Hard
  • Involves Electrical Skills, Stripping Wires
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What you need

Tools
Materials
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How to do it

Step 1

Mount Subpanel

Mount the subpanel about a foot away from the main service panel. Determine how far the wires will have to travel in the subpanel and pull wires (shown) or add cable and strip sheathing accordingly. Remove a knockout slug, slide the wires through, and clamp the cable.

Related: Basic Wiring Techniques You Need to Know

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Step 2

Plan Route

At the main service panel, plan the routes for the four wires: ground, neutral, and two hot wires (black and red). Strip the sheathing, remove a knockout slug, and clamp the cable. Route the neutral and ground wires carefully and connect them to their bus bar(s).

Editor's Tip
Editor's Tip

Professional electricians take pride in the way they run wires into a service panel or subpanel. In a well-wired panel, wires route in neat paths around the perimeter, making it easy to tell which wire goes to which breaker. More important, orderly wires are less likely to brush against hot bus bars, which would create a serious fire hazard.

Step 3

Strip Wires

Route, cut, and strip the red and black wires. Connect them to the feeder breaker. Snap the breaker into place.

Related: How to Draw Electrical Plans

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Step 4

Connect Wires

In the subpanel, route the feeder wires, cut and strip them, and connect to terminals. Connect the black and red wires to the hot bus bars, the neutral wire to the main neutral terminal, and the ground wire to the ground bus bar.

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Step 5

Finish Connecting Wires

Run cable for new circuits into the subpanel and clamp the cable. For each circuit, route wires around the perimeter, connect the ground wire to the ground bus bar, the white wire to the neutral bus bar, and the hot wire to a circuit breaker.

Related: How Ground Wires Can Help Protect Your Home's Electrical System

By BH&G Editors

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