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Question about photocell and switch

Posted by jimmyleon (My Page) on
Thu, Sep 27, 12 at 22:27

Several years ago when I put out a yard,post, light and added a photocell and dimmer switch. The light is still working properly. Since I have moved to where I now live I have added a post light. Put a photo cell on outside garage wall, switch inside the wall. I added a dimmer switch but dimmer didn't work. Photocell would turn on light but dimmer couldn't turn it off nor dim the lights. So I thought if that didn't work I would add a standard 15 amp switch and reduced bulbs to 75watt instead of 100 watt I was going to dim. Problem was that switch would control the light off and on but photocell wouldn't not work with the switch, light wouldn't never go off by photo. Wired the same way dimmer was wired. So I put the dimmer back on and now my light will come on at night, go off in morning but dimmer doesn't work to control the light. But if I add a standard switch I would have to manually turn the light off and on. Photo is wired red to black on light, black to black as source, white to white neutral. What is the problem with the switch and photocell??

Follow-Up Postings:

RE: Question about photocell and switch


I think the issue is that the Photocell to work properly needs to have 120v. WHen you put the dimmer in then you have less than 120v at the photocell hence the issue.

Some stuff from the net on the Mike Holt forum.

So in effect what you need to do is to have the Photo Cell be "upstream" of the dimmer. So the Photocell always has 120V. The Photo cell then supplies 120V to the dimmer only when it is dark.

Best, Mike.

Here is a link that might be useful: Dimmer Photo Cell discussion

RE: Question about photocell and switch

Thanks, Mike. I see your point. This would be the reason when a standard 15 amp switch is in, it is cutting off current to the photocell. Light can be controlled with the switch but photocell can't work. Would that be right? So I would need to rearrange some wiring. Get power to the photocell first and then back to the switch. Right? Power is coming to the switch box first right now. Thanks!!

RE: Question about photocell and switch

Using a dimmer and a photocell in series (in any order) is often the equivalent of having two dimmers in series.

The photocells & the dimmer both use a solid state switch (a TRIAC) and they are NOT designed to be used in series.

RE: Question about photocell and switch

Hi Jimmy,

Yes I think you need to rearange your wiring a bit.

I think a "standard" photocell has three wires. So you need I think to do this....

1) Photocell Black: connect to live, hot of your house
2) Photocell White: connect to Neutral, zero volts of your house
3) Photocell Red: connect to dimmer.
4) Connect other end of dimmer to light bulb
5) Connect light bulb to Neutral, zero volts of your house.

Hope this helps.

Best, Mike.

RE: Question about photocell and switch

Thanks, Mike. Yeah you are right. I did rearrange the wiring and put switch wires and sources wires in my outside box. I found some old notes I had kept from this website on the light I had put out before. Spencer, who is on this website, had helped me before. For anyone else here who might need this same help, here is how it is wired and you are correct--black on photo went to black in source, white on photo to neutrals, red on photo went to one switch wire, other switch wire went to wire to the light. It works fine and I can dim the lights and overide the photo cell if I want to or if photocell for some reason fails to go off when it is daylight. Thanks for yours and everyone's help here. This webpage is so helpful. Thanks!

RE: Question about photocell and switch

And you are still driving one solid state switch with another solid state switch.

NOT a recommend practice even if it appears to 'work.'

It can cause overheating and failure (as in burning components) in the second switch.

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