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#58356 - 11/07/05 05:58 PM Backfed Photocell?  
Redsy  Offline
Joined: Mar 2001
Posts: 2,056
Bucks County PA
A photocell will operate a lighting contactor. If I install a switch to bypass the photocell and energize the contactors coil, the bypass switchleg will also (back)feed into (red) photocell output leg.
Is this a concern?


Work Gear for Electricians and the Trades

#58357 - 11/07/05 06:03 PM Re: Backfed Photocell?  
Dnkldorf  Offline
Joined: Dec 2004
Posts: 1,064
nowhere usa
Not for me....

It is the same phase, right?

Your not really backfeeding it, your applying the same phase on the red wire, as if the photo cell was operating properly.


#58358 - 11/07/05 06:06 PM Re: Backfed Photocell?  
ShockMe77  Offline
Joined: Jun 2005
Posts: 821
Rahway, New Jersey
Not if its on the same phase. I've wired motion detector lights like this in the past. When the light switch is on, obviously the lights are on. When the switch is off, the motion feature controls the light. I think what you are describing is the same thing.

#58359 - 11/07/05 06:09 PM Re: Backfed Photocell?  
iwire  Offline
Joined: Jan 2003
Posts: 4,391
North Attleboro, MA USA
I do not see any code issue with it.

However another option would be the use of a 3 way switch (SPDT)

Common to contactor coil.

One terminal from constant feed.

One terminal from red of the photo cell.

You end up with ON or AUTO with this set up and no back feed to the red of the cell.

Make sure the EGC is large enough. [Linked Image] [Linked Image]


[This message has been edited by iwire (edited 11-07-2005).]

Bob Badger
Construction & Maintenance Electrician

#58360 - 11/07/05 06:40 PM Re: Backfed Photocell?  
Redsy  Offline
Joined: Mar 2001
Posts: 2,056
Bucks County PA
Thanks guys.

The phasing is OK.
I think I actually did this configuration once before, but I'm not sure.
My concern is damaging the photocell.


EGC, what's a EGC? [Linked Image]

[This message has been edited by Redsy (edited 11-07-2005).]

#58361 - 11/07/05 09:44 PM Re: Backfed Photocell?  
capt al  Offline
Joined: Jun 2004
Posts: 206
Norton, Ma USA
EGC = Equipment Grounding Conductor.


#58362 - 11/07/05 10:14 PM Re: Backfed Photocell?  
renosteinke  Offline
Cat Servant
Joined: Jan 2005
Posts: 5,316
Blue Collar Country
Not a problem. I usually do this very thing.

You are not "back feeding" the photocell. The photocell is nothing more than a switch. It does not draw any current.

#58363 - 11/07/05 11:11 PM Re: Backfed Photocell?  
Redsy  Offline
Joined: Mar 2001
Posts: 2,056
Bucks County PA
Thanks again guys.

[This message has been edited by Redsy (edited 11-07-2005).]

#58364 - 11/07/05 11:56 PM Re: Backfed Photocell?  
Larry Fine  Offline
Joined: Feb 2005
Posts: 693
Richmond, VA
Redsy, from what I understand, as long as the line (black) wire is hot, there's no harm in energizing the load (red) wire.

Larry Fine
Fine Electric Co.

#58365 - 11/08/05 08:09 AM Re: Backfed Photocell?  
Redsy  Offline
Joined: Mar 2001
Posts: 2,056
Bucks County PA

The line won't ALWAYS be hot when the red is fed from the bypass. Only when the timers contacts are closed.


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