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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?

  • I have a junction box with a top conduit that goes to one switch and one light.
  • The left side top conduit is the power supply coming from another junction box.
  • The bottom left side of the junction box has a conduit for a light and one switch.
  • On the right side are two conduits that are controlled by switch #2 which is wired through the bottom conduit.

These are Two Separate Rooms with Two Separate Switches

  • I need to know how to wire the orange wire which is confusing to me because that wire is coming from light fixture #1.
  • I think the wire should be black.
  • There are two wires with black tape and I need to know what they are used for.

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

home safety tips

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

  • For Example:
    • The voltage for most commercial light fixtures is typically 277 volts, which is not the same as the home electrical voltage for lighting which is 120 volts.
    • Since the voltage is different, the standard used to identify the wires is different as well.

A Warning about Commercial Electrical Systems

  • In the example of this electrical question, a handyman working in a commercial medical building which has a 277/480volt system poses a higher risk and danger of  electric shock and arc flash hazard because of the higher voltage. Therefore for your own safety,  I do not recommend that a handy-person perform electrical work in a commercial environment unless you are fully experienced and knowledgeable.
  • Working with electricity, especially higher voltage requires a Qualified Licensed or Certified Electrician.

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Electrical Wiring Diagrams

  • Home electrical wiring diagrams are an important tool for completing your electrical projects.
  • An electrical wiring diagram can be as simple as a diagram showing how to install a new switch in your hallway, or as complex as the complete electrical blueprint for your new home or home improvement project.

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Fully explained pictures and wiring diagrams about wiring light switches describing the most common switches starting with photo diagram 1.




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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. 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

    • 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.
      Dave


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