How to Wire a 200 Amp Subpanel

Introduction

Wiring a 200 amp subpanel can seem intimidating, but it is absolutely a do-it-yourself project if I take my time and follow proper safety precautions. A subpanel provides additional circuit capacity and allows circuit isolation for additions or renovations. I'll walk through the complete process step-by-step to help demystify subpanel wiring.

Reasons for Installing a 200 Amp Subpanel

There are several common reasons I may need to install a 200 amp subpanel:

Adding circuits - A subpanel provides additional breaker spaces to add new lighting, outlet, or appliance circuits. This allows me to expand electrical capacity.
Circuits for additions - When finishing a basement or adding on to my home, a subpanel provides a clean way to supply the new space without overloading existing circuits.
Outbuilding circuits - Wiring a detached garage, shed, or other outbuilding is made much easier by using a subpanel to provide dedicated circuits.
Renovations - Upgrading wiring, relocating outlets/fixtures, or modifying circuits is cleaner and safer by using a subpanel to isolate the renovation circuits.
Improving safety - Subpanels allow me to upgrade from outdated fuses to modern circuit breakers and bring wiring up to current code.

Subpanel Basics

Before getting into the step-by-step process, it helps to understand some key subpanel terminology and components:

Main Service Panel vs Subpanel

The main service panel is the primary electrical panel fed from the utility lines. It contains the main disconnect breaker.
A subpanel is installed after the main panel to provide additional circuits. It gets its feed from a circuit in the main panel.

Breakers

The main breaker in the main panel is rated for the full amperage of the electrical service.
The feed breaker in the main panel protects the subpanel feed wire. It is sized based on the subpanel rating and wire size.
Circuit breakers in the subpanel protect individual branch circuits. Standard sizes are 15, 20, and 30 amps for home circuits.

Grounding

Subpanels must be bonded to ground using a grounded conductor in the feed wire. This connects grounds between panels.
The ground bar and neutral bar in a subpanel must be kept isolated from each other. Grounds and neutrals are handled separately.

Electrical Permit

Most jurisdictions require an electrical permit for subpanel installation. I'll need to research permit requirements for my area and submit plans for review. The inspector will check my work after completion before giving final approval.

Tools and Materials

I'll need to gather the following tools and materials:

Tools

Voltage tester - To safely check wires are de-energized
Drill - For mounting panel and drilling holes
Hole saw - For knocking out panel cable entry holes
Hammer - To knock out panel breaker holes
Screwdrivers - Standard and Philips head
Wire strippers - To strip NM cable and ground wires
Linesman pliers - For bending conduit and pulling wires

Materials

200 amp subpanel - With enough breaker spaces for planned circuits
Mounting hardware - Appropriate for wall mounting surface
1 inch conduit - For feed to subpanel, use EMT or PVC
THHN wires - 4 wire feed - hot, hot, neutral, ground
Grounding rod - To earth ground subpanel
Ground wire - #4 bare copper from subpanel to ground rod
Appropriate breakers - For subpanel feed and branch circuits
NM / UF cables - For branch circuit wiring

Step-by-Step Installation

With tools & materials gathered, I'm ready to install the subpanel. I'll follow standard safety procedures and de-energize circuits before working. Here is an overview of the full installation process:

1. Choose Subpanel Location

Ideal location is a garage, basement, or utility area. I should aim for:

Close proximity to main panel for easier feed
Central location to branch circuit fixtures
Away from wet areas
Allow 36" clearance minimum around panel

2. Mount Subpanel

Securely fasten panel to wall studs if possible:

Mark stud locations
Allow for panel to be centered
Drill clearance holes for mounting hardware
Secure panel with lag screws or bolts

3. Install Grounding

Subpanel must be properly grounded:

Drive ground rod into earth ~6 feet from panel
Run #4 bare copper wire from rod to subpanel ground bar
Connect wire to ground bar and ground rod clamp

4. Run Feed Conduit

Run 1" feed conduit from main to subpanel:

Determine best route between panels
Drill entry holes in sides of panels
Attach conduit connectors
Run conduit continuous between panels

5. Pull Feed Wires

Carefully pull THHN wires through conduit:

Use plastic fish tape to pull wires
Loosely pull all wires at once to prevent friction
Leave 12-18" of extra wire in panels

6. Connect Feed Wires

Land and terminate feed wires securely:

Match wire colors to terminals (black-hot, white-neutral, green/bare-ground)
Attach grounds first, then neutrals, then hots
Torque lugs to spec - DO NOT overtighten
Insulate neutral and ground bars from each other

7. Install Main Breaker

Install main breaker in subpanel:

Match main breaker amp rating to subpanel (200 amps)
Remove panel cover
Snap or bolt breaker into place
Connect feed wires to breaker terminals

8. Install Branch Breakers

Add circuit breakers for branch circuits:

Plan circuits and select appropriate breaker sizes
Snap breakers into subpanelslots
Take care not to overload subpanel amp capacity

9. Connect Branch Circuits

Connect lighting, outlet, and appliance circuits:

Plan circuit routes and wire sizes
Pull branch circuit wires through rafters/joists
Use staples to secure cables
Pigtail and connect wires to breakers

10. Inspect and Energize

Call inspector to review work before energizing:

Energize once approved and signed off
Ensure neutral and grounds read 0V across bars
Methodically test each circuit at panel

Following proper planning, safety procedures, and this step-by-step guide, I can successfully install a 200 amp subpanel to expand my home's electrical capacity. Take it slowly and be meticulous for best results. Stay safe by de-energizing all circuits before working.