Photo-eye in series with time clock for school outside lights?

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sw_ross

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The maintenance guy described to me the situation. There is a photo-eye and a time clock controlling the outside lights at the school.
My first assumption was that the photo-eye would be in parallel with the time clock.

I had seen this before where a different school had it set up to rely on the time clock for normal daily operations, but if you had a day that was overly cloudy and dark the photo eye could turn the lights on during daytime hours.

When I tried to understand the setup once I got there I wasn't able to manually turn on the lights using the time clock (manual switch). Trying to interpret the conduits and conductors I decided which one went to the photo-eye, but the setup didn't layout like I expected.

I went up up to where the photo-eye was to confirm the wire colors, then taped off the photo eye. The return wire (red) came back to one pole of the time clock, giving power to that pole.
Then, when the time clock (based on programmed time) closes up that pole it the sends power to the line side (A1) of the contactor coil, closing the contactor and turning on the lights.

This seems messed up to me...

The coil will never get energized unless the photo-eye works in series with the time clock to send power to it.
Unless I'm missing something.

Am I thinking right about using the time clock in parallel with the photo-eye?
What would be the reason for the way I described this setup?
 
sw_ross said:
The maintenance guy described to me the situation. There is a photo-eye and a time clock controlling the outside lights at the school.
My first assumption was that the photo-eye would be in parallel with the time clock.

I had seen this before where a different school had it set up to rely on the time clock for normal daily operations, but if you had a day that was overly cloudy and dark the photo eye could turn the lights on during daytime hours.

When I tried to understand the setup once I got there I wasn't able to manually turn on the lights using the time clock (manual switch). Trying to interpret the conduits and conductors I decided which one went to the photo-eye, but the setup didn't layout like I expected.

I went up up to where the photo-eye was to confirm the wire colors, then taped off the photo eye. The return wire (red) came back to one pole of the time clock, giving power to that pole.
Then, when the time clock (based on programmed time) closes up that pole it the sends power to the line side (A1) of the contactor coil, closing the contactor and turning on the lights.

This seems messed up to me...

The coil will never get energized unless the photo-eye works in series with the time clock to send power to it.
Unless I'm missing something.

Am I thinking right about using the time clock in parallel with the photo-eye?
What would be the reason for the way I described this setup?
Click to expand...

Time clock in parallel won’t work.
if the eye calls for it, they come on. If the clock calls for it, they come on. There is no supervision.
time clock, then photo eye.
i have ran another wire from the bypass switch on an installation and tied it into the load side of the photo eye to turn it on with the switch.
 
Hv&Lv said:
Time clock in parallel won’t work.
if the eye calls for it, they come on. If the clock calls for it, they come on. There is no supervision.
time clock, then photo eye.
i have ran another wire from the bypass switch on an installation and tied it into the load side of the photo eye to turn it on with the switch.
Click to expand...
Why wouldn't they work in parallel?
At 6pm the time clock turns on the light... At 6am the time clock turns them off...
At 2pm on a dark dreary day the photo-eye turns on the lights...

I'm not sure what you mean by supervision?
 
sw_ross said:
Why wouldn't they work in parallel?
At 6pm the time clock turns on the light... At 6am the time clock turns them off...
At 2pm on a dark dreary day the photo-eye turns on the lights...

I'm not sure what you mean by supervision?
Click to expand...

It will work that way if that’s what you are after. I don’t really understand why you want a time clock in the circuit though. Photo eye turns them on when it gets dark, say at 5PM, or 8PM, depending on the season. The photo eye cuts them off at 5AM, or 8 AM, depending on season. Photo eye cuts them on at 2PM on a dark dreary day.

So so what’s the time clock for?
 
A time clock in parallel with a photocell will allow either to override the other (an OR logic gate).

A time clock in series with a photocell requires both to be on for the load to work (an AND gate).

The timer should have power 24/7 for the clock to remain set. How you wire it depends on the desired operation:

If you want the timer or the photocell to be able to prevent the lights from coming on, put them in series with the timer first, feeding the PC's black wire.

If you want the photocell to be able to override the timer to make the lights come on despite the time, put them in parallel, feed to PC black and load to PC red.
 
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sw_ross said:
Why wouldn't they work in parallel?
At 6pm the time clock turns on the light... At 6am the time clock turns them off...
At 2pm on a dark dreary day the photo-eye turns on the lights...

I'm not sure what you mean by supervision?
Click to expand...

You don't have a bad idea just a different one.

The set up you are currently dealing with works like this....
Series the photo cell through the time clock, set the time clock to come on early, say 3:00 PM, and to go off at midnight, then walk away. The result is the lights don't come on at 3:00 PM they come on at sunset all year long no matter when sunset happens, but they don't stay on all night long, they go off at midnight.
 
Hv&Lv said:
It will work that way if that’s what you are after. I don’t really understand why you want a time clock in the circuit though. Photo eye turns them on when it gets dark, say at 5PM, or 8PM, depending on the season. The photo eye cuts them off at 5AM, or 8 AM, depending on season. Photo eye cuts them on at 2PM on a dark dreary day.

So so what’s the time clock for?
Click to expand...

I totally agree with you! For simplicity, in this application, I'd just use the photo-eye.

im just trying to figure out why it is set up the way it is.

thanks
 
ActionDave said:
The set up you are currently dealing with works like this....
Series the photo cell through the time clock, set the time clock to come on early, say 3:00 PM, and to go off at midnight, then walk away. The result is the lights don't come on at 3:00 PM they come on at sunset all year long no matter when sunset happens, but they don't stay on all night long, they go off at midnight.
Click to expand...
Like in my upper example above. However, as above also, the PC should follow the timer. There is a chance the lights will come on when the timer first energizes the PC.

Hey, it just hit me: If you can separate the clock feed from the contact feed, you can insert the PC ahead of the contacts in the circuit.
 
ActionDave said:
You don't have a bad idea just a different one.

The set up you are currently dealing with works like this....
Series the photo cell through the time clock, set the time clock to come on early, say 3:00 PM, and to go off at midnight, then walk away. The result is the lights don't come on at 3:00 PM they come on at sunset all year long no matter when sunset happens, but they don't stay on all night long, they go off at midnight.
Click to expand...

Makes total sense!

One circuit, labeled security lights (lights above each door) operates by photo-eye only. So they're on all night.
The rest of the lights must be set up (using time-clock) to turn off at set time.
that makes sense.

The maintenance guy has only been there fo a few months so he really doesn't know anything about the lights.

Thanks
 
LarryFine said:
Like in my upper example above. However, as above also, the PC should follow the timer. There is a chance the lights will come on when the timer first energizes the PC.
Click to expand...

Correct

Hey, it just hit me: If you can separate the clock feed from the contact feed, you can insert the PC ahead of the contacts in the circuit.
Click to expand...

Yep, I'm sure you could. Who wants to think that hard on a work day though?
 
FWIW, AHJ requires time clock and photo cell in parallel in my area ( Miami/hospital). The parking lot lights have to be on life safety branch.
 
ActionDave said:
Time clock, set the time clock to come on early, say 3:00 PM, and to go off at midnight, then walk away. The result is the lights don't come on at 3:00 PM they come on at sunset all year long...
Click to expand...
Actually most dusk to dawn photo sensors come on for a minute or two when first powered up.
So lights will likely briefly come at 3pm when contactor comes in.

I would just stay with photo eyes at a school.
For a business, I'd use an astronomical timer.
 
This is one method of getting around using a time clock with astronomic capabilities. The standard time clock is set to whatever times you want it to be on or off. The photocell should be in series with the power to the lights. So, let's say you have the time set in the winter to come on at 4:00 PM. The clock activates through the contacts but the lights don't come on until it's actually dark out but lights still goes off at midnight when the clock opens the contacts. Now, let's say the actual time changes to the summer hours. The clock now closes the contacts for the light at what it believes is 4 PM (actually 5 PM) but the photocell doesn't allow the lights to come on until it's dark.

I don't understand why you would want to have the photocell in parallel with the time clock contacts.
 
Gold star, Larry, and ActionDave- you all have good points! Thanks!

I guess it depends on what the customer wants the lights to do.

Given your feedback, if they want them all to be on all night, for simplicity, just use a photo-CELL.

This seems to be the current setup for the "Security" circuit (entry doors). They're on all night.

The rest of the lights are fed off the contactor, which is controlled by the time clock and the PC in series. So, based off what you've described, they're set up to turn off at a specified time (~midnight). Obviously, the time clock has constant power for the clock.

This seems to be the current setup, with power going to photo-cell first then using the time clock to turn the lights off at a specified time through the contactor. Although the Security (entry doors) doesn't go through the contactor. They're fed directly off the load side of the photo-cell so they're on all night.

Thanks for the education! I can use this information to talk to the customer (maintenance guy/Principal) about how they want their lights to operate.

Primarily this project is to upgrade the lights to LED, but the maintenance guy has some frustrations about controlling the lights.
 
I think most of you know what I mean by “time-clock “...

what do do you call it? Time Switch? I’ve always heard it referred to as time-clock.

Sorry if im using incorrect terminology
 
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