Electrical Wiring for Light Switches

By Dave Rongey - Summary:

The Difference Between Commercial and Home Electrical Wiring: In this example a commercial medical building has a 277/480volt system.

Light Switch Wiring in a Commercial Building

Electrical Question: How do I wire two separate lights and switches in one supply junction box?

These are Two Separate Rooms with Two Separate Switches

This is a Commercial Medical Plaza in Laguna.
I really appreciate your help with this, and why it is wired this way.

This electrical question came from: Chris, a Handyman from Laguna, California.

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

The Difference Between Commercial and Home Electrical Wiring

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IMPORTANT: Here in the USA, commercial electrical wiring is not the same as home electrical wiring.

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3 Responses to “Electrical Wiring for Light Switches”
  1. http://www.ask-the-electrician.com is really a walk-through for all of the info you wanted about this and didn’t know who to ask. Glimpse here, and you’ll definitely discover it.

  2. Dave Rongey says:

    Hi Steve – yes, I know exactly what your describing because I have rewired several homes.
    Steve, The existing wiring will need to be identified so you understand the purpose of each cable. Once you have done this then the cables may be either dead ended or terminated, or spliced with a new power or circuit source in an existing wall switch or outlet box, or ceiling fixture box if the space of these boxes permits. I personally would not use a recessed light fixture box for a splice or junction box. Basically, if an old wire or cable cannot be removed then it should remain in an electrical box and capped off. If you install a new outlet or other box then yes, the older wiring can remain in its existing box where you may place a blank cover over it. You may also consider replacing the existing box with a deeper box which could contain both the old wiring and new wiring.

  3. Steve says:

    Hi, My question is rather simple yet after reading 20 different blogs have come to think it may need more thought. I am remolding my kitchen and it’s in a home built 50 some odd years ago. After removing the walls, insulation and ceiling the wiring used is BX (AC,MC?) depending on your definition. There is no way to remove the wire because they feed different parts of the house. I don’t know what the old electricians were thinking when they ran wire, what a mess. Anyway I want to replace all that I can but how do I connect the old feeds to a source? I don’t have space for juction boxes in these locations. I was told that the ceiling cables can be boxed inside the recess light can with a new power feed? Also can I leave the old cable in say a outlet box and switch boxes along side a new feed and outlet? I hope you understand what I’m trying to say here. Many thanks, Steve


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