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Installing an Electrical Sub-Panel

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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.

Adding a Sub-Panel

Electrical Question: 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, NJ.

Additional Comments: Very Interesting.

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

How to Install an Electrical  Sub Panel

What must be considered 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.

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


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.

  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.


  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.


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