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I have a set of front exterior lights on my house which are controlled by two 3-way switches, one in the garage and one in the front entry way. I would like to install a photocell so that I can leave the circuit on all the time and let the photocell decide when to switch the lights on and off.

I'm finding it very difficult to find a diagram of a photocell in a 3-way light switch circuit. Does anyone know if this is possible; and, if it is, what should the circuit look like? I've looked at various photocells online and they all seem to have three wires coming from them (red, white, and black).

Also, does it matter where the photocell is installed in the circuit? The circuit I'm interested in adding the photocell to has 4 fixtures on it between the two switches. I noticed that the photocells have a maximum wattage rating. I plan on using LED lights in these fixtures to keep the wattage down below the maximum rating of the photocell.

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  • Does power come to one of the lights, or to a switch? Where do you want to mount the photocell? Can you provide photos of the insides of the boxes involved? Are you OK with sacrificing one of the manual switches, or do you want both switches to still work? Can you run new wiring?
    – ThreePhaseEel
    Commented Jun 15, 2017 at 2:05
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    And most importantly -- do you want the photocell to override the switches, the switches to override the photocell, or the photocell and the switches to have equal control over the lights?
    – ThreePhaseEel
    Commented Jun 15, 2017 at 2:09
  • How would you get the photocell and the switches to have equal control over the lights? Put the photocell on one of the travelers? - Ooh I would totally do that just to mess with everybody's head.
    – A. I. Breveleri
    Commented Jun 15, 2017 at 3:31
  • @A.I.Breveleri -- I'd use the photocell to control a relay that is wired to act as a multi-way switch
    – ThreePhaseEel
    Commented Jun 15, 2017 at 11:45

2 Answers 2

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Yes.

The photocell is placed in series with the feed from the panel ahead of the switches. The white is the neutral, the black is the hot feed, and the red is the switched hot. Of course, this makes the circuit inoperable during the light of day and there will be no manual override.

I would install an astronomical timer like this one: https://www.amazon.com/gp/product/B004AP92N2/ref=oh_aui_search_detailpage?ie=UTF8&psc=1

This also goes in series with the switches in the circuit but it has a manual override and does not need to be placed outdoors. The built-in computer calculates the times for dawn and dusk for your lattitude and longitude. Those default start and stop times can be adjusted to your preferences.

Good luck and stay safe!

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What I have noticed is the three way doesn't necessarily control the lights meaning when it is dark the switches are hot but when you turn them off or on the light will stay on but if you have the switch in the middle neither off or on the light will be controlled by the switch. I ended up taking out the photocell since we have lightning restrictions so I put in a timer switch so the lights wouldn't be on till dawn.

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    Hello, and welcome to Home Improvement. It isn't clear what you're trying to say, or how it relates to the original question; would you add some context? And, you should probably take our tour so you'll know how best to contribute here.
    – Daniel Griscom
    Commented Sep 6, 2019 at 10:41

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