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The electrician installed a new wall switch in the kitchen, so that when I replace the fluorescent light, it can be turned on and off at the wall switch.

I am ready to install the new light.

In the ceiling, there is a bare copper wire that I am assuming is the ground and will be wired to a screw on the light fixture. There is a white wire - neutral, and a black wire- hot, and I know to wire white to white and black to black.

However, there is a second white wire and a second black wire, and they are wired together with a cap on them, and I am not sure how to connect those.

Also in the ceiling is an old two-pronged plug where you could plug something in, although I am not sure what you would ever plug in there. But perhaps the second black and white wires are for that plug, and the electrician just capped them together temporarily because they come from the same outlet.

So do I just connect all three whites and all three blacks together?

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Electricians can wire things multiple ways. A second set of black and white wires indicates that there is a load connected at this junction. You'll need to determine if the hot is indeed switched, and what other fixtures are also switched, for us to give a proper answer. If you're not comfortable using electrical testers to check for hot wires, then I'd recommend getting the electrician back to finish the job. –  BMitch Oct 7 '12 at 22:47

2 Answers 2

The white is a neutral that completes the circuit. If you see several of them wire-tied together, keep them together or else you could be interrupting circuits in the house.

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Generally true but not always. When you introduce a switch into the mix you're going to end up with wire uses not necessarily correlating to their colors. For instance, if your line comes into the switch box, and you go black to the switch, and black from the switch to the light, then black is hot, yes, but it's connected to the neutral terminal on the switch. –  The Evil Greebo Oct 8 '12 at 14:32

Most likely the second white and second black wires are the connection to the switch itself. If so, then what you've got is power line from circuit box to light, switch line from light to switch. (The alternate method is power line from circuit box to switch, switch line from switch to light - which would have been less confusing for you but he probably was dealing with old work by the sound of it.

How it works in your configuration (if I'm right) - imagine the electrical current like a flow of water. The power comes in from the breaker box on the black line (aka the hot line). The power then runs to the white line and down to the wall switch. When the switch is on it then runs back up the black line to the light. You connect black to black, and the power flows into the light, then out the white line. You connect white to white, and the power flows on down back to the breaker box, and out.

So - don't touch the second white and black. Just wire the light's white to the lonely white and black to black the same way.

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+1, just reread the question to see that the black and white were connected together. In that case, I suspect you're correct. Standard safety rules apply (shutoff breaker, test before you touch, etc). –  BMitch Oct 7 '12 at 23:56
    
And once you are done, mark all the hot lines that are not black or red with black tape or a black marker. It will make the next visit to that box much easier. –  bib Oct 8 '12 at 13:00

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