Switch Legs?

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  #1  
Old 09-14-00, 07:23 PM
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Hi there: The more I read about wiring switches the less I understand. I have two wires coming(black\white) into a two- terminal switch that controls my bathroom light fixture. I have installed a bathroom fan and ran 14/2 to another switch on the wall beside the light switch. Is there anyway to hook up the new switch, drawing power from the old switch?
 
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Old 09-14-00, 07:46 PM
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In your case, if I understand you correctly, you cannot do what you hoped to do.
You have a dead end or loop switch, which means you have no neutral in that existing switch box.
You need a source of power or circuit. One should exist at the light but I presume that tis is a wall fixture.
Since the fan is in the ceiling, I would suggest getting a source from the attic then feed the fan box, and run another dead-end line down to your new switch.
If you do it this way, you would put the white of the feed wire to the white of the fixture lead. The black of the pair feeding your switch will be the switch leg and go on the black of the light. The two left, black from the source feed and white of the switch pair get wirenutted together.
At the switch box you will have two wires and they will go on the two screw therminals of the switch in any configuration.
 
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Old 09-14-00, 08:15 PM
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Hi: Thanks David for your prompt reply. I'll have to do it like you suggest. The part I don't understand is that this light switch circuit continues into the kitchen where it powers two plug-ins, one of which has a branch circuit out to the outside wall and then goes on into the living room. It seems like this branch circuit is similar to what I'm trying to do. Two wires fed by what I'm assuming to be two hot wires. I don't know.
 
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Old 09-14-00, 09:11 PM
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Hi Lost,
I had to jump in here. There's no way a switch leg can supply power to outlets beyond that switch. If the "circuit" continues into your kitchen that's understandable, but the source of that kitchen power is not the switch box but probably the ceiling box where the switch leads. Think of it this way, you have a source wire, black and white. It leads to the light. If you connect white to the silver terminal and black to the colored terminal the lamp will light. However you can't turn it off. To run a switch leg, you must "break" the black. Never break the neutral. Run another cable down to the switch. Now from source, neutral will go directly to the light, hot will go down to the switch and back up to the light, enabling you to turn it on and off. When making your connections at the ceiling box (breaking the black), run white down to the switch and black back up to the light. This way when you make your connections at the light you have both black and white wires, white from source and black from the switch. Also you should see why you can't take power from the switch, even though you have a black and white wire, they are essentially both hot and the only time code allows a white wire to be attached to a black wire. Hope I didn't over simplify this but it's important to understand switches and how the colors of the wires can be confusing.
 
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Old 09-15-00, 05:34 PM
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Lost one

I guess that I have a need to jump in there too. I have a question that may blow away both previous replies if my suspisions are correct.

If the two other guys are understanding what you are saying is correct then they are right in what they are saying. We may have an advantage with me jumping in. I am an electrical inspector in a jurisdiction where john Q never wired before public do 90% of the work in this area on their own homes.

Sometimes the language to the talker and the listener is not the same.

When you say you have two wires, and then say you have black and white, is it possible you are calling a cable a wire and really have two cables with a black and white each in the switch box that you are trying to get power. If this is the case then your laymen talk is being translated to skilled talk in a misinterpretation type manner. What you are saying may not be what we are hearing.

Do you have two non metallic sheathed cables entering into the existing switch box containing a black and a white each?

OR

Do you have one non metallic sheathed cable entering into the existing box containing only one black and one white total in the box?

Hope we get the story translated right then we can answer correctly. The previous posts may be right. Past experience dealing with laymen electricians and with their way of talking can be confusing to us as to exactly what you are saying.

Hope this may help

Wg
 
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Old 09-16-00, 08:53 AM
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wg makes a good point. I often wonder about that myself, is this guy talking about wire or cable? I usually take the safe way out and mention that the boxes should be wired "exactly" as I think they are in order for the circuit to work properly.
For instance, in my previous post, I didn't even answer Losts' question. I just tried to explain a switch leg for him. I think that will go a long way in understanding circuits.
WG, what do you think about adding the fan to the light switch? I don't like it personally but it's a lot easier to wire. The bath light is probably above the medicine cabinet. It would be easier to just remove the medicine cabinet and hook the fan to the wires coming from the existing light switch.
 
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Old 09-16-00, 10:10 AM
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Hi there: I want to thank everyone for their input and I'll try to connect to the junction box in the attic. I've inspected it and I find I have about four whites conected together, three or four blacks connected to a white and three blackes connected to themselves. A real dog's breakfast. I will have to diagram the wires to see if I can make some kind of order to them.
By the way, there is only one cable with two wires coming to the existing switch.
Thanks again.
 
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Old 09-16-00, 11:37 AM
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I guess you guys read his question right. If only one cable is in the switch box, then no grounded conductor can be present, just a switch leg.

To answer Handyone's question. I really would not be concerned with adding a bathroom exahaust fan to the light fixture to be switched at the same time. The load of a bathroom fan is usually small and most likely would not be noticed on the circuit.

The only hold back is listening to the fan every time you turn the light on.

Might be an idea for him to think on.

Good thinking

Wg
 
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