Motion porch light... how easy ,and yet impossible

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Old 10-04-17, 08:42 PM
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Motion porch light... how easy ,and yet impossible

House has a porch light, controlled by a switch.
I've since had my vehicle plundered by kids going down the street at night, going into vehicles. They got about six of us neighbors in a row, and surely will come back for more later.

Now, above the front door, outside on the porch, is an unused coverplate, with a mount hole.
Upon removing this plate, there is a wire, capped together.
If you uncap the wire into two pieces, the porch light turns off.
So, this is the live wire for the porch light. Fantastic.

How easy it would be, to just get a motion switch- attach it to this live wire, and then when the porch light is left ON, the motion light will kick off, scaring off the would-be plunderers.

Not so fast.
The motion light has 3 wires, not two- black, white and red.
So just putting a motion detector light in line, in this convenient way, looks to be anything but convenient.
Attach the black and white wires to the line, and you get a very dim light.
Anything else, doesn't work at all.
Am I screwed?
 
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Old 10-04-17, 09:09 PM
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Upon removing this plate, there is a wire, capped together.
I assume you really mean two wires. If you have a black and white what you found is a switch loop. A switch loop has no neutral so it won't work as you already found out. If you can replace that 2-conductor cable with a 3-conductor cable it would work.
 
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Old 10-04-17, 09:24 PM
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What I've basically got is two wires sticking out of the siding of the building, going who knows where. Its clearly part of the circuit for the porch light though, and is activated by the switch inside the house. When they are not connected, the porch light goes off.

What I could possibly do is route another house wire down to the spot (like 14-2), perhaps by crawling into the attic, and dropping it down , somehow finding the spot on the porch and pulling it through, and then hooking the other end up to the house power.
That would leave me then with four wires- the two new ones for house power (black and white), and the two ends of this mysterious wire that completes the porch circuit.

What then?

If a neutral is needed, then what if say, each end of the mystery wire were attached to the black and red wires on the 3 wire motion sensor, and then its white wire was attached to a new wire, which was routed back and connected to any white (neutral) wire in the house, say the neutral side screw on an outlet?
 
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Old 10-04-17, 11:51 PM
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All conductors must be in the same raceway (sheath or conduit) so you can't just run more wires. Tell us all the wires at the light.
 
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Old 10-05-17, 05:08 AM
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Can you please post a picture of the Junction box and the switch wiring? I think terminology is getting in the way of a solution .
 
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Old 10-05-17, 06:16 AM
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You can get a motion light with a buzzer or siren or something, I do believe.
 
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Old 10-05-17, 07:45 AM
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What I'm saying is I am trying to come up with a solution without taking a sledgehammer to the wall, so-to-speak and doing a complete house rewiring.

OK here are the pics. In the 2nd you can see what was behind the metal cover directly above the door, which evidently used to be another porch light.
There are the ends of two wires coming through the siding.
The next picture shows the light, wired to the side of the house.
The first picture shows the security light, which easily mounts to the cover plate above the door. Had it been wireable to the two loose wires, this would have been a 5 minute project. And the motion detector would be in the perfect place- right above the door, and watching the front yard and my vehicle.

I fully understand this is NOT a 5 minute project, but am just trying to be smart and make it less than a contractor job, and without damaging the house.
 
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Old 10-05-17, 07:54 AM
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This seems to go right along with my original line of thinking. In this case, "12-2 w/g wire" would be the black wire, and the two wires going into "Motion Detector" would be the two wires sticking out of the siding. As far as the "Outdoor light", there would be another neutral wire coming from that going back to the power source.
But of course, it doesn't work that way.
 
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Old 10-05-17, 09:50 AM
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Ah, this is what I was looking for. Finally!
But how to make it work with what I've got?
 
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Old 10-05-17, 10:11 AM
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Here I moved the stuff around and made a diagram of what I want to do.
I'm thinking at this point the red and black wires of the sensor should connect to each of the wires coming out of the siding. Black goes to the live wire coming from the switch, red to the 'onward to the light' wire. And then the white (neutral) wire gets routed somehow back to the neutral at source,
But... can the white from the sensor be connected to any neutral wire in the house, or does it have to be the exact same neutral at the source with the original black wire?
 
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Old 10-05-17, 10:16 AM
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If you have #14 wiring currently in use..... use #14 not #12.

That wiring sticking out of the siding with no apparent box should not affect the existing light. Opening those wires and having the existing porch light turn off indicates that cable is incorrectly wired in series.... not parallel to the working light. That can be changed.

A picture showing the front of the house with boxes would be helpful.

We know what you need to do. It's the how to run the wire is the question.
 
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Old 10-05-17, 11:30 AM
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The biggest problem I assume is this:

I need to have 3 wires coming out of the spot above the door, to mount the sensor.
I can access the attic above, where I can get to both the power source coming from the switch, and the wires going to the light.

If I can somehow get a 14-3 wire coming out above the door, and the other end going up to the attic, where everything else is... will I be in business?
 
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Old 10-05-17, 01:39 PM
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If I can somehow get a 14-3 wire coming out above the door, and the other end going up to the attic, where everything else is... will I be in business?
Wires are individual conductors. What you need is a 3-conductor cable between the power in for the light and the sensor. You need to determine if power in is at the switch or the light. You need to open both boxes and describe the wiring for us.

The two wires, presumably cable, over the porch need to be rerun/bypassed or placed in a box for reasons of safety and code compliance.
 

Last edited by ray2047; 10-05-17 at 02:07 PM.
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Old 10-05-17, 07:54 PM
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I've got it, thanks folks!

The scenario I described worked fine- light is clicking away beautifully. Main power to the black and white wires, red wire to light black and white wire from light back to white neutral at power source. Just had to run one more wire from the sensor to the power in the attic, and straigthen it all out (y)
 
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Old 10-05-17, 08:17 PM
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Just had to run one more wire from the sensor to the power in the attic,
You can not run one wire. All wires must be within a cable or conduit.
 
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