Extending Electrical Circuit Wiring

By Dave Rongey - Summary:

How to Add Electrical Wiring for a Outlet and Light Switch: Extending Electrical Circuit Wiring for an Outlet and Light Switch.

How to Add Electrical Wiring for a Outlet and Light Switch

Electrical Question: How can I put a junction box into the circuit wiring before a light fixture so I can add an outlet light and switch.

  • I would like to continue an electrical circuit by adding another outlet and a light switch and light, and I have run into a problem.
  • The only access to the end of a circuit I can tap into is from a 3way light fixture.
  • The existing 3-way switch has the power coming into it and then to the light and then to the second switch.
  • My question is, is there a option of how to put a junction box on the wire before it hits the light because I would like to have continuous power to future outlet and light and switch.
  • I don’t want the new branch to be controlled by the 2 existing switches.


This electrical question came from: Jake, a Handyman from New York, NY.

Electrical Answer:
Dave’s Reply:
Thanks for your electrical wiring question Jake.

How to Add Electrical Wiring for a Outlet and Light Switch

Application: Adding Electrical Circuit Wiring.
Skill Level: Intermediate to Advanced – Best installed by a Licensed Electrical Contractor.
Tools Required: Basic Electricians Pouch Hand Tools, electric drill, auger bits and extension cord.
Estimated Time: Depends on personal level experience, ability to work with tools and install electrical circuit wiring.
Notice: Installing additional electrical circuit wiring should be done according to local and national electrical codes with a permit and be inspected.

Extending Electrical Circuit Wiring for an Outlet and Light Switch

Common Problem when Installing Circuit Wiring from a Light Switch

  • Extending Electrical Circuit Wiring
    Jake, you cannot extend the wiring form the light fixture that is controlled by the two three way switches unless the switch box is the location of the power source.
  • Adding onto an Electrical Circuit
    To add circuit wiring for another light switch or outlet a power source must be located which contains a circuit power source which includes the white neutral wire, the black power wire and the ground wire.
  • Locating a Power Source
    With this question, it may be best to extend circuit power from another source, such as a wall outlet or a wall switch that has both a neutral and hot as needed for the continuous power source.
  • Available Circuit Capacity
    The circuit must have available capacity to provide additional power for the devices that will be added.
  • Electric Circuit  Cable Type
    When extending an electrical circuit the cable type and size must be the same as the existing circuit wiring that will be spliced into.

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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.


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FAQs Frequently Asked Questions and Comments

4 Responses to “Extending Electrical Circuit Wiring”
  1. Dave Rongey says:

    Hi Jerry,
    I understand your wiring problem and this may help you: If the added junction box will be accessible from the attic space then this method is allowed. However, if the junction box will be inaccessible then it is not allowed.

    How to Make the Wire Longer
    You may want to see if you can reconfigure the path of the cable by removing the cable staples, which may allow you to get a little more length from the wire so it reaches the new exhaust fan. Make sure the cable is well protected, and then secure the cable in place.
    Enjoy your new exhaust fan,

  2. Jerry Brown says:

    I am replacing a bathroom exhaust fan located in the ceiling. The existing electrical wire will not reach the new exhaust fan. Can I extend the wire by installing a junction box which will end up behind the ceiling dry wall?

  3. Dave Rongey says:

    Hi Albert,
    What you have described is known as a Multi-Wire Circuit, which is where two circuits from different phases or buss share the same neutral. You can tap into one of these circuits as long as the circuit has the available amperage and the neutral remains under the amperage rating of the circuit wiring conductor.
    Keep in mind that the circuit breakers that provide the power for these two circuits, circuits #6 and #8 should have a tie bar across the two breaker handles. The reason is because both of these circuit must be OFF before working on the circuit wiring to eliminate any voltage potential on the neutral wire.
    I hope this helps you,

  4. Albert Maruggi says:

    This is crazy I have two circuits coming into a 1 gang shallow outlet box, circuit #6 is on the top outlet. This is in the middle of a run as it goes to a junction box then another outlet. The hot wire from main panel, then the hot from the junction box share same pole. White to junction box on opposite of that pole.
    The bottom outlet has hot from main panel from circuit 8 and white from panel for circuit 8 plus a ground. It looks like then that this is a shared neutral.
    My question is how do I tap into this outlet for hard wire under cabinet lighting. It’s the most convenient source to get to. The next closest power source is the main room light which is on a 3 way switch. I am completely stumped.


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