Thursday, July 14, 2011

one black wire and one white wire coming into the box

Switch Leg

A picture of a Toggle light switch.Image via Wikipedia

QUESTION: Hi Robert, and thanks for taking the time to consider my question. I live in a 115 year old house in AL that still has the cloth coated aluminum wiring and porcelain insulators (thankfully no longer used, just to express the age of the house) I wanted to upgrade the main light switch in my daughters bedroom to add another switch that controls a not yet existing outlet for a plug in closet light. Unfortunately, there is only one black wire and one white wire coming into the box connecting the existing switch. Can you help me? with instructions on how to wire the second switch, then going to the outlet? I figured working in one of the oldest cities in the country, you might have run into something like this. Maybe you can also give me some insight on how my house might be actually be wired. If you need any pictures, I can take and add them too. I really thank you for any help.

ANSWER: Hi Steven,

You are playing with fire. That is more than a figure of speech in this case. You should not mess with this old electric unless it is your intention to replace it. The cloth and aluminum becomes brittle over time and  is not a good idea to for homeowners to learn/practice on electrical system this old. Adding to an old system is also a no-no.

---------- FOLLOW-UP ----------

QUESTION: I'm sorry for the confusion; that wiring, although still present, isn't used any more. It was replaced (I think in the 70's with a brown 2 conductor wire which is what I'm dealing with, 1 black wire and 1 white wire. I know the box has been replaced because new grounded wiring has been added. In the attic, there is one place where there a bunch of wires tied together. I'm somewhat fimiliar with modern wiring, but this one is puzzling me.

Follow up Answer:

Now that makes more sense. So the switch only has a black and white wire. that tells me you only have a switch leg in the box. That means the hot and neutral are in the light box. They are the wires that will make the light go on.

The hot in the light box get diverted to the switch on the switch leg. The hot black gets connected to the white of the switch leg and goes down to one side of the switch. When the switch is "On or Closed" the power returns to the light on the black wire. 

Your switch doesn't have a 120 volt feed. Only a switch leg with No neutral wire that wire is in the light and you will need that to power your new light. I would just rewire both lights and run 14-3 to the switch. The 3 wire will have the hot, neutral and the switch leg. Then you will have all the wires you need to add a new light.Related articles
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