Home » Electrical Wiring Directory » Sub-Panel » 6 Comments
« Where and How to Install a Green Ground Screw in a Panel How to Ground a Panel for a Detached Shop »

Installing an Electrical Sub-Panel


By Dave Rongey - Summary:

Thinking about installing a Sub Panel? Here is what must be considered first, and you may find that you really do not need a sub panel at all.


Guide for adding a Sub-Panel

Electrical Question #1: What is the best way to install a sub panel?
Project #1

  • I want to install a sub panel.
  • Can I install a sub panel from another 100 amp main panel?
  • What size wire cable should I use?

This electrical question came from: Barbaro, a Handyman from Perth Amboy, New Jersey.

Electrical Question #2: Can I add a sub panel to a sub panel?

Project #2

  • My electrician was supposed to provide for three 220volt outlets in my garage sub panel, but he used all the available breaker space for other circuits.
  • Now there is one 220volt outlet circuit with unconnected wires in the panel and no where to go.
  • How can I get this one outlet wired up, without replacing the entire sub panel?
  • Should I replace the sub panel it with a larger panel?

Thanks, Jack

This electrical wiring question came from Jack, in Los Angeles, California.

Dave’s Reply:
Thanks for your electrical wiring question Barbaro and Jack.

Considerations about Installing an Electric Sub Panel

Circuit Breaker Panel

Application: Adding a Sub Panel.
Skill Level: Intermediate to Advanced – Best performed by a Licensed Electrical Contractor, Not Recommended for Homeowners.
Tools Required: Electricians pouch of hand tools and the various power tools necessary for installing the sub-panel.
Estimated Time: Depends on the type and size of the panel and available access to the project area.
Precaution: Any existing electrical wiring within the immediate area that may interfere with the installation of the sub panel should be identified and turned OFF and Tagged if necessary. Working in an electric panel is dangerous due to arc flash hazards and the possibility of electric shock.
Notice: Installing additional electrical wiring and a sub-panel should be done according to local and national electrical codes with a permit and be inspected.

Before Installing an Electrical  Sub Panel

Many electrical panels allow tandem, twin or quad circuit breakers to be installed which will allow the installation of a few more circuits, so research the type of panel that you have to see if it will allow installing circuit breakers of these types.

  • Before installing a sub panel the following should be considered:
    • Does the existing electrical panel have enough electrical capacity for the additional load of the new sub-panel.
    • Does the existing electrical panel have the physical space available for a circuit breaker that would feed the new sub-panel.
    • The size of the sub panel and the cable size that is required for the new sub-panel will depend on the electrical load that will be connected to the new sub-panel.

Factors that Determine the Size of a Sub Panel

  • List all the electrical devices that will be added to the panel.
  • Identify any devices that require a dedicated circuit.
  • Determine the number of spaces that will be required for circuit breakers in the new sub panel.
  • Calculate the total connected electrical load that will be added to the sub panel.
  • Using the total connected load and the number of required circuits, determine the amperage of the sub panel and total number of circuit breaker spaces that will be needed.
  • NOTE: The amperage size of the sub panel may be less than the total connected load. The actual panel amperage may be factored upon the circuits and equipment that is connected to the sub panel.

More about Electric Panels and Circuit Breakers

2-pole-circuit-breaker

Circuit Breakers
An Illustrated Guide to Circuit Breakers Complete with Diagrams and Photos from an Expert.

Circuit Breaker Panel
The home circuit breaker panel contains several circuit breakers that are carefully installed by experienced electricians and electrical contractors.

Electric panel
home-electrical-circuits
House Wiring Circuits and Circuit Breakers
This article looks at common 120 volt and 240 volt house wiring circuits and the circuit breakers that are installed identifying the types and amperage sizes used in most homes.

Home Electrical Wiring
Electrical Wiring
Electrical Wiring
Home electrical wiring projects with pictures and wiring diagrams.


« How to Make an Electrical Cable Splice How to Repair a Tripping GFCI Outlet »


Learn How to Wire it Right with my
Complete Guide to Home Electrical Wiring
Perfect for Homeowners, Students,
Handyman, Handywomen, and Electricians
Includes:
Wiring GFCI Outlets
Wiring Home Electrical Circuits
120 Volt and 240 Volt Outlet Circuits
Wiring 3-Wire and 4-Wire Electric Range
Wiring 3-Wire and 4-Wire Dryer Cord and Dryer Outlet
Troubleshooting and Repair Electrical Wiring
Wiring Methods for Upgrading Electrical Wiring
Electrical Codes for Home Electrical Wiring
....and much more.

» Click here to learn more about Home Electrical Wiring «
  repair electrical wiring  


Be Careful and Be Safe - Never Work on Energized Circuits!
Consult your Local Building Department about Permits and Inspections for all projects.

FAQs Frequently Asked Questions and Comments

6 Responses to “Installing an Electrical Sub-Panel”
  1. Bob Romano says:

    Want to Install a sub box with a 20 amp circit breaker 120 volts. Main circit breaker is full. I want to use two wire with ground to sub box from Main box. Where do I connect wires from Main box to sub box with the 20 amp breaker.

    • Dave Rongey says:

      Hi Bob,
      If the panel does not have room for another circuit then a twin or tandem breaker may be the solution, it just depends on your panel.
      When adding a sub panel the panel must be fed from a circuit breaker in the main panel. This whole process must be carefully planned out and is not something that can be easily explained here, and for your safety this is not recommended if you are not experienced.
      This type of project should be done with a permit and inspected – for your protection.
      Dave

  2. David Eshiet says:

    Thanks DAVE for educating me, I have improved a lot at my work.
    Please I need to ground cable, but the environment is very swampy, what doIi do, if we dig water comes out and covers the excavated hole,what do we do?

    • Dave Rongey says:

      Hi David,
      I’m not sure where you are, but your local area building authority must have specific methods for installing a ground system, so be sure to consult them.
      You be have to install a longer ground rod, or multiple ground rods.
      If the domestic water system enters the dwelling through a metallic pipe then this will serve as at least one ground source.
      Concrete foundations can be grounded using a 20 foot #2 rebar to bond to or install a 20 foot length of copper ground wire into the foundation before it is poured. The size of the ground wire will depend on the size of the electrical service.
      Be sure to see the electrical code section of the web site for more information about grounding.

      Dave

  3. Wayne M says:

    I have a sub panel that has a 240 line for a stove that is not being used.
    Question is how can I change over 240 to two 120 circuits?

    • Dave Rongey says:

      Hi Wayne,
      120 volt circuits require a separate neutral wire, and if the existing 240 volt stove cable is a 4-wire cable which includes a separate neutral and ground wire then the neutral wire may be shared with the black and the red or the two power legs to create the two 120 volt circuits. The grounds for the 120 volt circuits are spliced with the ground of the stove cable as well. The existing 240 volt stove circuit breaker will need to be replaced with a 2-pole 15 or 20 amp circuit breaker depending on the size of the wire that will be used for the 120 volt circuits or the desired amperage.

      Dave


6 Comments

Thanks for your Comments and Quick Questions!

Please make sure your question is about the topic on this page, which is:
Installing an Electrical Sub-Panel


Comments or questions posted here are open for Quality Discussion and Participation - Spam will be deleted.



*