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I currently have 4 fixtures, 2 recessed above the garage and 2 enclosed lamps near the front door. They're controlled by a switch that has a builtin timer. I'd like these lights to come on around sunset and go off at a reasonable time (like 11pm).

But I'd also like them to come on when motion is detected. So if someone were to approach the house after the scheduled period ends, I want the lights to come back on.

I'm struggling to figure out how one might do this. At the very least I'd need a few motion sensors, but how would that work? Do the motion sensors act as a 3 way switch?

Or is this not possible and the only way to pull off a similar effect is to have separate motion activated lights? (Probably easier but not as pleasing to the eye)

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    This can be done, but it would be a very complicated wiring scheme. Without knowing exactly how it is wired now it is hard to say how to accomplish this. You'd have to wire it with a photocell to turn them on, a timer to turn them off, and a motion detector to back feed other times.
    – Speedy Petey
    Dec 19, 2015 at 14:29
  • There's often a photocell built into the motion detector, to save power during the day and provide light in heavy stoms. I think that can be leveraged. Easier with the home-automation approach.
    – keshlam
    Dec 19, 2015 at 17:08

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That can be done, but it's not a standard setup.

The old-style solution requires a box somewhere with relays in it. The switch, timer, and motion detector are wired to the relays, and their controlled output contacts are wired in the appropriate combination to produce the behavior you want. That combination is then used to control power going to the light. You might have trouble getting a home inspector to approve this if it isn't done by a pro... and I'm not sure even then.

The modern solution would be to use home automation components. Replace the existing switch with one that can be remotely controlled and that also informs the central control unit when it has been switched manually. Install a motion detector that talks to the central control unit. Then set that controller's clock correctly, and program it to signal the switch to turn on and off in response to the proper combination of these inputs. Much easier to install, passes code, probably no more expensive after everything is accounted for, can be built upon if you want to do other fancy home control later. RECOMMENDED SOLUTION.

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  • there is nothing in the NEC that forbids a UL-listed relay from being used within its ratings in dwelling unit wiring -- if worse comes to worse, you can treat it as a miniature Article 409 setup, i.e. an "industrial control panel" that controls a few lights. :)
    – ThreePhaseEel
    Dec 20, 2015 at 2:06
  • THIS IS THE RIGHT ANSWER. You should use relay isolation if you want to piece this together without home automation controller. But seriously. HA is super cheap these days. We're talking $250 for the components to do what he wants, PLUS dick with the lights form his phone while he's anywhere with internet connectivity. Look into Mi Casa Verde. I use this for my ZWave network, and it does exactly what Matthew is asking for, for me, right now. There are dozens of other, possibly cheaper head-ends for ZWave.
    – Billy left SE for Codidact
    Jan 6, 2016 at 5:51
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No No NO, This is very easy. and cheap.

Put the timer switch and the motion detector in parallel.

Just be sure to keep the whole rig on the same hot phase.

Only oddity about this method is that if one element turns the light on, the other cannot turn it off. It's highest takes priority.

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  • That sounds very promising. Any chance you could expand on how to do that? (aka dumb it down for an electrical newbie) my timer switch occupies a box with 2 other switches. I believe there is a neutral, a load and a line wire going to it. I assume that the motion detector would be attached to the same load, are you saying that it will also need to be attached to its own line so that the timer isn't responsible for providing power to the motion detector?
    – Matt
    Dec 19, 2015 at 22:45
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    @MatthewLevine -- what he's saying is to wire the motion detector's line to the timer's line, the motion detector's load to the timer's load, and the motion detector's neutral (if it uses one) to the timer's neutral.
    – ThreePhaseEel
    Dec 20, 2015 at 2:07
  • Yes, 3 is right. Gang the lines and gang the loads. It's the neutrals that get tricky. Often the motion detector requires neutral too. It sounds like you can make all the connections in the one switch box, that'll make it easier. Word to the wise, test it all after the wire nuts are secure but before you jam in the wires and button up the enclosure.
    – Trout
    Dec 21, 2015 at 2:13
  • STOP IMMEDIATELY. You need to get confirmation from the manufacturers of both the motion and the timer before you wire them in parallel. Here's why: They were probably not designed to be backfed hot input from their hot output conductors. If they are very simple devices, its probably fine. If each turn the light off by isolating the load then it's fine. But what if they turn the light off by switching the load from hot to neutral. Timer goes off, motion happens and BOOM. ARC FAULT. You could isolate them with a relay in front of each, or ideally, use home automation to replace both.
    – Billy left SE for Codidact
    Jan 6, 2016 at 5:46
  • Billy don't be rude.
    – Trout
    Jan 6, 2016 at 23:43

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