What's The Reasoning For This?

[Seven-Delta-FortyOne]

Why is the lighting being run through a timer after the photocell?

 

[petersonra]

So it only comes when it is dark and the timer says it is ok to turn the lights on

 

[Seven-Delta-FortyOne]

Well, yeah, but.....

Why not just one or the other?

 

[hmspe]

It gets darker later in the day in the summer than it does in the winter. With just a timer you have to reset the start time throughout the year. With the photocell the lights can come on at dusk no matter the time of year.

I prefer astronomic time clocks over photocell systems.

 

[LarryFine]

Well, yeah, but.....

Why not just one or the other?

Note that the PC and timer contacts are in series, which means they both must call for lighting.

(This is an 'and' gate; if they were in parallel, they would form an 'or' gate)

Thus, the timer prevents the PC from calling for lights outside of the set hours; an 'off' override.

This is often used where the lights need to be on early and late in the day, but not overnight.

If they were in parallel, the timer would prevent the PC from extinguishing the lights; an 'on' override.

 

[hbiss]

Why not just one or the other?

I've done the same thing myself. The photo control is dusk to dawn but you may want to turn the lighting off at say midnight. Also, a daytime storm can cause the photocontrol to turn on. So, you set the timeclock to turn on at maybe 5PM so the lights don't come on in the middle of the day or go on and off.

-Hal

 

[augie47]

A lot of the shopping centers did theirs that way. The didn't want the lights to come on at dusk and turn off once all the stores were closed.
If they used just the timer it was difficult to set the "on" time due to seasonal changes. As hbliss notes, you set the timer "on" time early enough to assure lights came on at dusk but not on cloudy days and you set the "off" time at the customers request, *most often we would set them about and hour past request in case the timer was a bit off.

 

[Seven-Delta-FortyOne]

Having them not run all night makes sense. Didn't think of that.

 

[hillbilly1]

Yeah, it’s a photo cell on, time clock off deal. Automatically adjusts for dusk, then when the stores close, it turns off the parking lot lighting. Usually though, there is another contactor for security lighting that stays on all night. Sometimes there is two sets of trippers in the time clock to turn the lights back on in the morning if a business opens early, such as a breakfast restaurant. They did it the easy way. If latching contactors are used, it’s a little more control work. Also I’ve seen electricians wrongly put the power for the photocell after the time clock.

 

[mtnelect]

With the increase in crime, and all the homeless camping out around our warehouses ... all of our Maintenance Contract customers told us to bypass the time clocks and keep them on with the photocell only.

 

[ptonsparky]

With the increase in crime, and all the homeless camping out around our warehouses ... all of our Maintenance Contract customers told us to bypass the time clocks and keep them on with the photocell only.

Yes, if the homeless can’t see while on the property your customers could be liable for injuries. Not really joking.

 

[mtnelect]

Yes, if the homeless can’t see while on the property your customers could be liable for injuries. Not really joking.

In Los Angeles and other cities this is a major problem. All of our warehouse customers have hired extra security to combat theft and vandalism. These indusial complexes are large businesses areas, with 18 wheelers coming and going 24 hours a day, and some staying over until next day.

 

[Seven-Delta-FortyOne]

OK completely different subject than the original, but I’m going over these plans and I don’t bid a ton of new commercial, so lighting contactors are pretty unfamiliar to me.

Fully understand what’s contactor is and what it does, but this is a single 20A circuit with some perimeter led lighting around a community building.

So why route it through a contactor?

I can’t even find a single circuit lighting contactor enclosure with a timer and HOA switch. Most are set up for multiple circuits.

 

[mtnelect]

OK completely different subject than the original, but I’m going over these plans and I don’t bid a ton of new commercial, so lighting contactors are pretty unfamiliar to me.

Fully understand what’s contactor is and what it does, but this is a single 20A circuit with some perimeter led lighting around a community building.

So why route it through a contactor?

I can’t even find a single circuit lighting contactor enclosure with a timer and HOA switch. Most are set up for multiple circuits.

1) Install a timeclock
2) Install a photocell
3) The timeclock with trippers turns on at say 3:00 pm and powers the photocell
4) The photocell turns on at sun set.
5) The photocell turns off at 12:00 am midnight from the timeclock

 

[Seven-Delta-FortyOne]

I know how to wire it.

First question was why you would have both. I guess if you want the lights off before the sun comes up, you’d use both. I get that now.

Now I’m kind of wondering why they have it drawn with a contactor. You don’t need a contactor for a single 20A circuit, you can wire the PC and timer direct, in series, with no need for a contactor.

 

[mtnelect]

This may be off topic but ... We have to do maintenance on these warehouse after hours, and I am ccw permitted.

 

[hbiss]

this is a single 20A circuit with some perimeter led lighting around a community building.

So why route it through a contactor?

Probably boiler plate spec but not a bad idea. If additional lighting is added and the voltage was changed little needs to be done. In many of my cases, the control voltage is from a different circuit than the site lighting.

I can’t even find a single circuit lighting contactor enclosure with a timer and HOA switch. Most are set up for multiple circuits.

I always build it myself. On a backboard: Tork timeclock and lighting contactor (in enclosure) offset nippled to a 4x4 trough below them. Lots of time the auto-off-on switch is wanted in the manager's office, not in the electrical room.

-Hal

 

[mtnelect]

Probably boiler plate spec but not a bad idea. If additional lighting is added and the voltage was changed little needs to be done. In many of my cases, the control voltage is from a different circuit than the site lighting.


I always build it myself. On a backboard: Tork timeclock and lighting contactor (in enclosure) offset nippled to a 4x4 trough below them. Lots of time the auto-off-on switch is wanted in the manager's office, not in the electrical room.

-Hal

In high crime cities, you need flood lighting 24/7 ... no need for flood lighting to be off at all.

 

[hbiss]

In high crime cities, you need flood lighting 24/7 ... no need for flood lighting to be off at all.

Ok, no problem. Just don't turn it off.

-Hal

 

[hillbilly1]

1) Install a timeclock
2) Install a photocell
3) The timeclock with trippers turns on at say 3:00 pm and powers the photocell
4) The photocell turns on at sun set.
5) The photocell turns off at 12:00 am midnight from the timeclock

Wrong, photo cell must be powered at all times. That is the biggest mistake a lot of electricians make. When photocell is first powered, it is default on, the lights come on, then go back off. Then at dusk, they turn back on. You have to isolate the time clock contact, which is easily done by moving the clock power wire.