120V Wiring Diagram Question

[Wayne Whitney]

Hello,

I'd like to control a porch light with both a switch and a motion detector. Switch on, light on; switch off, light on motion detector. I've come up with two ways to wire this using a 3 Way Switch (DPST, right?). Here are diagrams of the hot side:

Incoming ------------- 3 Way Switch ------------ Light Power | A | B Common | | ---- Motion ---- Detector

Incoming ------------ 3 Way Switch ---------- Light Power Common | A B | | | ---- Motion ---- Detector

The second way would be easier to wire (less box fill at the switch), but I think it wouldn't work, as it presents the Motion Detector with

120V at its output when the switch is in position B. I'm assuming the Motion Detector will require a neutral and will be quite unhappy to have 120V at its output. Is this correct?

Is everything OK with the first diagram?

Thanks, Wayne

[RBM]

[Mortimer Schnerd, RN]

You're making this much too tough. Wire up the motion detector as either an add-on or as a replacement to the original porch fixture. Do nothing at the switch. The switch should always stay on. Motion will turn the light on. If you want to turn the light on without any motion, just flick the switch off and then right back on. The lights will come on and stay on. To reset back into motion detection mode, just turn the switch off and wait a few minutes before you turn it back on.

I've got motion sensors all the way around my house and they all work this way.

[AutoTracer]

Wire it like a normal light with two 3-way switches or one single pole switch. Motion detectors often have a feature where it will remain on if you flip the switch off and on. Do it again and it goes back into motion detecting mode. No fancy wiring required.

[Joseph Meehan]

Check out some of the current like of fixtures and motion detectors. I believe you will be able to find what you want without changing any wiring. I believe you can find one that switch off light off, switch on light on, switch on again light controlled by motion detector.

[Wayne Whitney]

Thanks.

Right, this is my second diagram. My concern here is about damaging the motion detector when the lamp is on via the switch: I'm assuming the motion detector will have 3 wires, white neutral, black incoming power and red outgoing switched power. The above wiring means that when the lamp is on via the switch, the motion detector will "see" the following set of connections:

White wire Neutral Black wire Unconnected Red wire Hot

Is this OK for the motion detector? If not, would it be OK if the Black wire were also hot? That would be easy to arrange by just using a SPST switch.

Cheers, Wayne

[Wayne Whitney]

Yes, another poster suggested this, and I had this when I rented. If there were existing wiring I wanted to keep, I would definitely use a product like this to avoid rewiring. However, I'm replacing the knob and tube wiring anyway, so I can wire the circuit anyway I want. And I prefer the functionality I described (on = on, off = motion detector) to the functionality these retrofit products have. So all I need to do is figure out the wiring.

BTW, it looks like I'll need to use a separate light and motion detector, since I want a decorative ceiling mount light fixture, and all the decorative exterior lights with motion detectors built in are wall mount lights. I guess with ceiling mount a built in motion detector would be obscured. I'll just install a separate ceiling box a couple feet away for the motion detector.

Cheers, Wayne

[Wayne Whitney]

Yes, what I want to do is non standard, but I have to redo the wiring anyway, so it won't be that hard to execute, if I can figure out the wiring. I definitely prefer the user interface I describe to the user interface that overloads the "on" position of a normal switch (i.e. on has two different meanings).

Basically what I need to know is this: if I take a stand alone motion detector with three wires, white neutral, black incoming power and red outgoing switched power, and I hook the white to neutral, the red to hot and leave the black unconnected, does it damage the motion detector?

Cheers, Wayne

[RBM]

[Wayne Whitney]

Great, thanks very much for the info. That makes for a simpler wiring arrangement, with one less cable and less box fill at the switch.

Cheers, Wayne

[gfretwell]

I suppose YMMV but I have Heath motion detectors wired in parallel with no problems. They see 120v on the output when the other one is on.

[Joseph Meehan]

I would also prefer switch control vs program control for this situation.

[Goedjn]