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How to Install and Wire a Sub-Panel

Summary: Electrical Sub-Panel wiring considerations for the home complete with pictures. Careful planning for your Sub-Panel with immediate and future load considerations will help you understand how to size your Sub-Panel. This information will help as you consider a Sub-Panel and its size.

How to Install and Wire a Sub-Panel the Right Way

Make a List of all the things you plan to use

120 volt devices
Electrical Convenience Outlets
GFCI Protected Outlets

240 volt equipment
Motor Loads:
Hot Tubs [see the Hot Tub Page]
Well Pumps
Air Conditioners
Sub-Panel Considerations-
Correct amperage for all existing loads and future requirements.
Considerations to help determine Sub-Panel Circuit Requirements:

Important Factor: Find out if the Main Service or the Panel that will supply the Sub-Panel Circuit have adequate Load Capacity and space for the needed circuit breaker.

How big should your Sub-Panel be ? (Watts and Amperage)
This will help you consider the circuits to be served by the Sub-Panel including general purpose electrical outlets and any special equipment which will be needed.

Special Considerations:
Large 220 Volt Loads such as Welders, Air Conditioners, Motors, Well Pumps and the like may require larger size wire and conduit to provide the necessary current this equipment requires. Be sure to list all the label requirements and manufacturers specifications.
Long Distances from the power source will produce Voltage Drop, especially over 175 feet. A 2% Voltage drop factor and correction will most likely require an increased size of the wire and conduit.

Wire Types and Capacities
Cables and common wire types

Devices and Junction Boxes
Select the right box for your application

120/240 Volt Sub-Panel Circuit Requirements
4-Wire System consisting of:
2-Insulated Power Conductors (Black & Red)
1-Insulated Neutral Conductor (White)
1-Ground Conductor (Bare or Green)

Don't Make This Mistake!
[click pictures to enlarge]

Illegal Electrical Sub-Panel Electrical Sub-Panel


More about Wiring a Sub Panel

  • Grounds and Neutrals in Electrical Panel
  • How to Wire Grounds and Neutrals in Sub Panels – all the neutrals and ground wire and terminal bars must be separated from each other, and your sub feed should be a 4-wire cable that has a separated insulated neutral wire and a separate ground wire.
  • Sub Panel Grounding and Neutrals
  • Understanding Grounding for Sub Panels: When you add a second electrical panel with separate neutral and common bars, do you ground the common to the box along with a ground rod connection?
  • How to Install a Sub Panel for an Attached Garage
  • Planning and Installing a Garage Sub Panel: Do This Before Installing a Garage Electrical Panel, Check the Main Panel, Select the Wire Type and Wiring Method, Check the Wiring Path, Outlets and GFCI Requirements, Electrical Code Compliance.
  • Considerations When Planning An Electrical Sub Panel
  • How to Plan for a Sub Panel Installation: Planning the right amperage and cabling for a sub-panel used in a basement, garage and other locations.
  • How to Plan for a Sub Panel
  • Planning for an Electric Sub Panel: Identifying Panel Circuits and Connected Loads. Sub Panels are installed and used for several reasons including expanding the circuit breaker capacity of the main electrical panel.

Learn more about wiring a sub panel


Questions about Sub-Panels

Questions about Wiring Panels

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