# 208V Photocell



## Tsmil (Jul 17, 2011)

k_buz said:


> Something I've always wondered...
> 
> If I pick up a 208V photocell, it has 3 leads...black, red, white. Obviously you are only switching one leg of the 208V so why do they even sell these "208V" cells?


Yes, they only switch one leg. That is why you always shut off at breaker before servicing. 

I was instructed to always switch the lead supplying shell. This would be the safest if someone changed lamps with power on.


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## HARRY304E (Sep 15, 2010)

k_buz said:


> Something I've always wondered...
> 
> If I pick up a 208V photocell, it has 3 leads...black, red, white. Obviously you are only switching one leg of the 208V so why do they even sell these "208V" cells?


You will find the same thing for a 480 Volt fixture..


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## TimChaput69 (Nov 14, 2011)

That's an awesome question! Now I'm wondering what the winter white lead on a 120V photocell does!!


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## TimChaput69 (Nov 14, 2011)

I've got a couple bad 120v cells at work, Monday I just might crack one open and see!!


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## Tsmil (Jul 17, 2011)

TimChaput69 said:


> That's an awesome question! Now I'm wondering what the winter white lead on a 120V photocell does!!


Photocell requires power to operate. Without neutral or L2 in the case of 208 it would be much like a tv with only one wire connected to power.


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## TimChaput69 (Nov 14, 2011)

Tsmil said:


> Photocell requires power to operate. Without neutral or L2 in the case of 208 it would be much like a tv with only one wire connected to power.


I understand that but the question that I'm coming up with is if a neutral is not required in a 208V cell then why is it needed in a 120V cell? Ponderous man.....F'n ponderous man!!


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## Tsmil (Jul 17, 2011)

TimChaput69 said:


> I understand that but the question that I'm coming up with is if a neutral is not required in a 208V cell then why is it needed in a 120V cell? Ponderous man.....F'n ponderous man!!


In 208 there is no neutral. You use L1 and L2. This is your supply. For 120 you use L and Neutral for your supply. The photocell doesn't care if it is a neutral or not, only that it is supplied with the correct voltage.


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## TimChaput69 (Nov 14, 2011)

Tsmil said:


> In 208 there is no neutral. You use L1 and L2. This is your supply. For 120 you use L and Neutral for your supply. The photocell doesn't care if it is a neutral or not, only that it is supplied with the correct voltage.


So back to the OP's question, why can't you use a 120V photocell on a 208V circuit? Unless they're wired differently then what's the difference? Not trying to be an ass....just now that I think about it he's right, whats the difference?


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## TimChaput69 (Nov 14, 2011)

Maybe I'm just the idiot and am stuck on something stupid but the more I think


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## TimChaput69 (Nov 14, 2011)

Sorry lost the keyboard!! I must be over thinking the whole thing I guess.......my wife always tells me I'm "swift"!!


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## Tsmil (Jul 17, 2011)

All photocells actually work on the same voltage. But they need something like a transformer or voltage divider to change from source supplied. A 120 volt photocell would have a transformer or voltage divider with a 120 volt primary. 208 volt photocell would have a 208 volt primary. None of them care whether it has a neutral or not, just that it has the right voltage between the 2 wires supplying power.


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## mbednarik (Oct 10, 2011)

I installed a 120v photocell switching a 208 lighting circuit. I just ran a neutral to the white lead, one leg to the photocell, photocell to the light, then the other leg to the light. So the photocell control only see's 120v, but the contacts have 208 on them when opened.


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## Tsmil (Jul 17, 2011)

mbednarik said:


> I installed a 120v photocell switching a 208 lighting circuit. I just ran a neutral to the white lead, one leg to the photocell, photocell to the light, then the other leg to the light. So the photocell control only see's 120v, but the contacts have 208 on them when opened.


Works for me


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## TimChaput69 (Nov 14, 2011)

Tsmil said:


> All photocells actually work on the same voltage. But they need something like a transformer or voltage divider to change from source supplied. A 120 volt photocell would have a transformer or voltage divider with a 120 volt primary. 208 volt photocell would have a 208 volt primary. None of them care whether it has a neutral or not, just that it has the right voltage between the 2 wires supplying power.


That would make sense then. If they are wired differently. I'm still gonna crack a old 120V cell and a 208V cell open and see!!


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## k_buz (Mar 12, 2012)

Ok, I dug out a cell labeled 208V (Intermatic 4223C). It says in the instructions that these cells are self adjusting and can be used for 120V loads, but once used for 208 or 277, they can only be used for that voltage. If you wire the cell for 120V, you get the same result, but you can then use it for 208V or 277V in the future. The reason I got confused was because the wiring diagrams all show a neutral going to the cell, so I've always wired them for the cell to run off 120V.


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## TimChaput69 (Nov 14, 2011)

k_buz said:


> Ok, I dug out a cell labeled 208V (Intermatic 4223C). It says in the instructions that these cells are self adjusting and can be used for 120V loads, but once used for 208 or 277, they can only be used for that voltage. If you wire the cell for 120V, you get the same result, but you can then use it for 208V or 277V in the future. The reason I got confused was because the wiring diagrams all show a neutral going to the cell, so I've always wired them for the cell to run off 120V.


Good to know...at work we stock 120V and 208/277V photocells. If there is really no difference between them that makes repair, and maybe cost, an easy solution.


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## TimChaput69 (Nov 14, 2011)

Again, I'm gonna crack a couple open and see what's what! I'll bring them home and take pictures cause I can't take pictures at work.


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## A Little Short (Nov 11, 2010)

I installed a new wall pack a few months ago and put on a new cell too. The S/H gave me the wrong cell. I needed a 120V cell and they gave me a 277V one. The light came on (in daylight) but wouldn't turn off. New cells turn on when power is first applied, then turn off after a few seconds. This one did not. I just thought that I had gotten a bad one so I took it off and went to get a replacement. That's when I noticed it was a 277V.
So I do know a 277V cell won't work on 120V!


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