Photocell question...

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chevyx92

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Had a co-worker ask me this this morning and I couldn't come up with the answer. If you have some 208v volt wall packs and want to use a photocell to control them why can't you use a 120v photocell? Why does it HAVE to be rated 208v when all you are doing is breaking one leg of the 208. A 120v is on one leg so why can't you just use a 120v photocell? The 208v photocell has Blk, Red, White. Thats just breaking one leg of the 208v. Understand what I'm trying to say?
 
chevyx92 said:
Had a co-worker ask me this this morning and I couldn't come up with the answer. If you have some 208v volt wall packs and want to use a photocell to control them why can't you use a 120v photocell? Why does it HAVE to be rated 208v when all you are doing is breaking one leg of the 208. A 120v is on one leg so why can't you just use a 120v photocell? The 208v photocell has Blk, Red, White. Thats just breaking one leg of the 208v. Understand what I'm trying to say?
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The photocell has an integrated circuit built into it that combines the incoming phases and then sends them to the lamp. The integrated circuit wouldn't work, IMHO, with a 120 volt photocell since the voltage would not be high enough to trigger the integrated circuit components.

But that is just my opinion.
 
It will work, but it's a bad design, since you're only turning off one of the ungrounded conductors. Some poor, uneducated and unlicened maintainence man could get zapped if the photocell shut them off, but the power was still on.
 
The supply voltage supplies the operating power for the photocontrol electronics. Connecting a 120V control to a 208V source would destroy it.
 
electricman2 said:
The supply voltage supplies the operating power for the photocontrol electronics. Connecting a 120V control to a 208V source would destroy it.
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one side of the 208 source is only 120. He's talking about only using one leg, not both.
 
peter d said:
This would not be allowed by 410.54.
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Huh? what version of the Code you reading? 2008 says "410.54 Pendant Conductors for Incandescent Filiment Lamps" It has (A)-(F) sections...

edit: 410.93 may apply?

second edit: I found it- you were speaking of the 2005 code, 410.54 (B) which has been relocated to 410.93 in the 08 Code, I think.
 
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jerm said:
Huh? what version of the Code you reading? 2008 says "410.54 Pendant Conductors for Incandescent Filiment Lamps" It has (A)-(F) sections...

edit: 410.93 may apply?
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2005.

I don't own the '08 yet because the two states I work in aren't on it. :)

I threw the code reference into my original post to eliminate further confusion.
 
I'm with you now Peetteerrrr. I don't have the hard version yet for the same reasons (we anticipate 2008 being adopted in OK on July 1) but I've got the online version on speed dial. :)
 
jerm said:
one side of the 208 source is only 120. He's talking about only using one leg, not both.
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I guess I am a little slow tonight, can you clarify this? If he has a 208V source, where is the 120 coming from?:confused:
 
electricman2 said:
I guess I am a little slow tonight, can you clarify this? If he has a 208V source, where is the 120 coming from?:confused:
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In the case of these lights in the OP, the 208 is derived from two 120 volt "legs" of a 3-phase 120/208 volt wye service.
 
electricman2 said:
I guess I am a little slow tonight, can you clarify this? If he has a 208V source, where is the 120 coming from?:confused:
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One leg of the 208. It's a 120/208 system. 208 phase to phase, 120 to ground.
 
if you're usin a 120v P/C, how is it getting it's neu? if you pulled 208 to it and only breakin 1 leg, other goin straight through. You plan on pullin 2 hots & a neu for the 120 p/c?? just buy a 208-277v p/c .....or did I miss this one all together??
 
SiddMartin said:
if you're usin a 120v P/C, how is it getting it's neu? if you pulled 208 to it and only breakin 1 leg, other goin straight through. You plan on pullin 2 hots & a neu for the 120 p/c?? just buy a 208-277v p/c .....or did I miss this one all together??
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If you have a 208v photocell with a blk, red and white.....how would you get your neutral. Same thing. Photocell needs the neutral.
 
BackInTheHabit said:
The photocell has an integrated circuit built into it that combines the incoming phases and then sends them to the lamp. The integrated circuit wouldn't work, IMHO, with a 120 volt photocell since the voltage would not be high enough to trigger the integrated circuit components.
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What??? :confused:​
 
chevyx92 said:
If you have a 208v photocell with a blk, red and white.....how would you get your neutral. Same thing. Photocell needs the neutral.
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Well, you get your 120v from the panel, why not pull a neutral to the PC as well?
 
480sparky said:
Well, you get your 120v from the panel, why not pull a neutral to the PC as well?
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Because if you hooked it up that way you'd be in violation of 2005 410.54 (B) or 2008 410.93. You have to switch both ungrounded wires. Just use a 120v photocell with a 120v 2p lighting contactor instead. Anyone make a 208v photocell? Never seen one.
 
480sparky said:
It will work, but it's a bad design, since you're only turning off one of the ungrounded conductors. Some poor, uneducated and unlicened maintainence man could get zapped if the photocell shut them off, but the power was still on.
Click to expand...

I agree that it's a bad design and also illegal but if anyone is dumb enough to use a photo cell as a disconnect they are not going to be around long anyway. :grin: :grin:
 
jerm said:
Because if you hooked it up that way you'd be in violation of 2005 410.54 (B) or 2008 410.93. You have to switch both ungrounded wires. Just use a 120v photocell with a 120v 2p lighting contactor instead. Anyone make a 208v photocell? Never seen one.
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Does this section apply to all luminaires, or just Lamps & Auxilliary Equipment (whatever that is)?

I believe what the OP is doing is creating a controller, not a disconnect.
 
jerm said:
Because if you hooked it up that way you'd be in violation of 2005 410.54 (B) or 2008 410.93. You have to switch both ungrounded wires. Just use a 120v photocell with a 120v 2p lighting contactor instead. Anyone make a 208v photocell? Never seen one.
Click to expand...


Here's one..

http://www.tork.com/pdf8w.htm
 
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