How to Install an Electrical Subpanel

Installing anything with wires and electrical work can be tough. We are here to make it easy for you with this how-to on installing an electrical subpanel.
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If the service panel does not have room for new circuit breakers and you cannot use tandem breakers, a subpanel may 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 one, 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" but instead be labeled "lugs only." It may be a different brand than the main panel.

Have the inspector approve the subpanel, the feeder cable, and the feeder breaker.

Shut off the main breaker in the service panel before you begin.

  • Start to Finish 2 Hours
  • Difficulty         Projects Kind of Hard
  • Involves Electrical Skills, Stripping Wires

What you need

Tools

  • Screwdriver
  • Hammer
  • Voltage tester
  • Flashlight
  • Strippers
  • Lineman's pliers
  • Long-nose pliers

Materials

  • Subpanel
  • Mounting screws
  • Approved feeder cable
  • Staples or cable clamps
  • Approved feeder breaker
  • Breakers for the new circuits

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.

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).

Step 3 Strip Wires

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

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.

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.

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