Add a light to an existing circuit

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  #1  
Old 12-15-05, 08:01 PM
briansharon01
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Add a light to an existing circuit

Ok, I'm hitting a brick wall with this one.
I'm quite sure I'm missing something obvious. (I'm an amateur, but can usually figure these things out)

I have a light connected to a single-pole switch. Only one set of wires come to the switch, so I'm understanding it to be at the end of the circuit. I want to add a second light controlled by the switch-- so the switch turns on/off two lights simultaneously. I *thought* I just needed to wire the second light in series:

Black (hot) comes into the switch, black from switch to 2nd light, white (black) from 2nd light to white (input). (the first black and last white are the two wires that were originally attached to the switch before adding the 2nd light)

But it's not working. If I do this, the 2nd light is lit, and the original light is not, which totally doesn't make sense to me. If I put the 2nd light in parallel with the switch, it toggles between the two lights.

I'm trying to avoid having to run more wires, but am thinking I need to run wires from the light in order to make both of them in parallel with the switch. Any thoughts?

Thanks.
 
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Old 12-15-05, 08:29 PM
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If there are only two wires in the switch box, they are not what you think - they are both coming from the light - one comes in hot and the other goes back out hot/not because of the switch. The juice is going to your light first and then to your switch. I'm guessing you assumed it went to your switch first and then the light.
 
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Old 12-15-05, 08:34 PM
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Originally Posted by briansharon01

I'm trying to avoid having to run more wires, but am thinking I need to run wires from the light in order to make both of them in parallel with the switch. Any thoughts?

Thanks.
Now you're thinking right.

Put the switch box back how you found it, open up the light fixture box, and run your new wire from there.

The two wires in the switch box put the switch in _series_ with the light bulb's HOT conductor. Fixtures must be connected in _parallel_ with your power feed in the box where the existing light fixture is located. That is, the neutral is never switched.
 
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Old 12-15-05, 08:34 PM
briansharon01
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I thought that, but when I tested the wires, it indicated the black was hot and white neutral (I took the circuit tester and put one connection to a wire and the other to the ground, and same for the second wire -- only the black came back hot).

If the two wires come from the first light, why can't a second be placed in series with it?

I think I may be a little confused on this...
 
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Old 12-15-05, 08:35 PM
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The wire to the switch creates a switch loop. There is no neutral wire, both are hot.

The bottom line is that you can't add your new light from the switch (unless you replace the wire from the light to the switch first). The easiest way to add a light controlled by the switch is to connect the new light to the existing light.
 
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Old 12-15-05, 08:46 PM
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Originally Posted by briansharon01
I thought that, but when I tested the wires, it indicated the black was hot and white neutral (I took the circuit tester and put one connection to a wire and the other to the ground, and same for the second wire -- only the black came back hot).

If the two wires come from the first light, why can't a second be placed in series with it?
Only the black came back hot because the white one goes thru the bulb filament to the white neutral that goes back to the load center.

The only way you can use those two wires in the switch box is if you disconnect the switch and reconfigure the switch loop so it's in parallel with the fixture instead of in series. That does not do you much good since your light would be on 24x7.

When I get confused I sit down and draw a diagram of the whole circuit. You might want to try that. I like a whiteboard since I make a lot of mistakes. Use different colors for hot and neutral and label all the wires black and white. You will see that the white wire from the switch to the fixture is along the HOT path. For all the rest of the wires, hot is black or red and white is neutral.
 
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Old 12-16-05, 12:22 PM
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Similar situation

Can I piggyback on this post?

If I wanted to add a second light similar to this but on a separate switch in same box, would I run wire from first to second light, then from second light to second switch?


I have a room that is poorly lit, I want to add a fixture using the same switch box.
 
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Old 12-16-05, 12:56 PM
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Originally Posted by Stumped1
Can I piggyback on this post?

If I wanted to add a second light similar to this but on a separate switch in same box, would I run wire from first to second light, then from second light to second switch?


I have a room that is poorly lit, I want to add a fixture using the same switch box.

It would be best to start a separate thread so we don't get confused as to who we are helping.

We can't answer your question without more information. Your existing setup may or may not be like the other posters. There are two possibilities:

1. The power goes to this switch first, then to the light. If this is the case, you will have two cables entering the switch box. The two black wires will each connect to the switch, and the two white wires will connect together with a wire nut.

2. The power goes to the light first, then to the switch. If this is the case, you will only have one cable entering the switch box. It's black and white wires will both connect to the switch. The white wire may (should) have been "reidentified" as a hot wire with electrical tape or magic marker. This setup is called a "switch loop", and is what the other poster had.


In case one, you can just run power to the new light from the switch box. In case two, you will need to run power from the old light to the new, plus a switch loop to the switch box.


Check out the switch box and tell us which situation you currently have.
 
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