Anything wrong w/ using PLC and contactors to control exterior lighting?

[Todd0x1]

Congrats on diving down the programming rabbit hole!

For remote I/O over Ethernet, just buy more Ethernet-enabled Click PLCs. They're as cheap or cheaper than standalone I/O, and you always have the option of putting some local "smarts" in each if you need it.

For the master PLC, I'd actually recommend the BRX line from A.D. They're more expensive, but they have some extremely useful instructions for an application like this. They have a GETTIME instruction that will update the PLC's internal realtime clock when programmed to do so. Most of the Click PLCs have a realtime clock as well, but no automatic way to update them from a remote time server. The Click's RTC accuracy/drift isn't exactly awesome (I know this firsthand), so someone will occasionally have to update it to keep it accurate.

The BRX can be set up as an Ethernet I/P master, and the Clicks as Ethernet I/P slaves, so using them as I/O should be a snap. I don't think you even need to put any code in the Clicks when used as Ethernet I/P slaves, if memory serves.

FInd a photocell with a relay output if you want to interface it to the PLC. You may not have to though - since the PLC has a realtime clock, you can match ON/OFF to civil dusk and dawn throughout the year, and it'll account for DST if you program it to.

Don't use a separate timer. That'll be a pain to maintain and (re)program. "Is the timer doing it, or is it something in the PLC?" If you need a user interface to adjust settings, add a small HMI. AutomationDirect sells the C-more Micro. They're quite reasonable cost-wise, and work well. The programming software is pretty straightforward too. Look at it this way - you can use it as an opportunity to learn more controls programming

https://www.automationdirect.com/adc/shopping/catalog/hmi_(human_machine_interface)/c-more_micro_panels/4_inch_panels_-a-_accessories/ea3-t4cl

SceneryDriver

Thank you for these suggestions, that does sound like a better way to do it with more flexibility. For this project, I am leaning toward my original concept to keep it simple. The main purpose of even using the PLC is to use the existing ethernet infrastructure to get control over to the remote buildings. The lighting control is simple time clock + photocell, with manual overrides. From the customer's viewpoint they have a normal timer for their maintenance people to fiddle with and the PLC is behind the scenes making it all work. That said, I will likely take another look at implementing this in the manner you suggested.

 

[kwired]

I have never programmed a PLC before, I finally made time to play with the Click PLC I had sitting here. I made a program that used a couple inputs to control an output, with one of the inputs triggering a timer. (basic I know but the goal was to get it to do something, didnt need to be complex) I know have an understanding of how these work and I feel like it is a good solution for the lighting control project. Next I need to order a Modbus TCP I/O unit and get the two units communicating.

The lighting will be controlled by 3 idifferent means: Time Clock, Photocell, Manual on/off. For the time clock I was thinking to use a standalone time clock vs trying to do it in the PLC. Intermatic has a 7 day panel mount time clock. Having a more 'normal' time clock would be more user friendly for whoever ends up maintaining this and the PLC can live in the background.

I appreciate everyone's thoughts and comments on this.

You don't need to know the core language of the PLC to do some basic stuff, you just need to know ladder diagram logic, as that is essentially all you are entering for your logic, and with PC interface that is common anymore all you do is look at that logic on your screen. There are some more advanced functions that are more complicated but anyone that can read simple ladder logic can program some basic inputs and outputs to turn on/off based on the state of the inputs. Next most critical thing is to learn how the internal timer relays work, as timing features is a major reason to use such a controller in the first place and then maybe at least some the basic analog input and output features.

 

[Todd0x1]

You don't need to know the core language of the PLC to do some basic stuff, you just need to know ladder diagram logic, as that is essentially all you are entering for your logic, and with PC interface that is common anymore all you do is look at that logic on your screen. There are some more advanced functions that are more complicated but anyone that can read simple ladder logic can program some basic inputs and outputs to turn on/off based on the state of the inputs. Next most critical thing is to learn how the internal timer relays work, as timing features is a major reason to use such a controller in the first place and then maybe at least some the basic analog input and output features.

My first program had an output controlled by an internal timer which was triggered by a falling edge NO contact. Press button and when you let go of the button the output turns on and stays on for 5 seconds then turns off.

 

[tortuga]

I was thinking I could use a PLC located in the utility building which would drive one or more local contactors to switch the lighting circuits that originate from that location plus a Modbus I/O module driving a contactor at each of the four structures. I suppose a 508 shop would have to make the panels up.

I do this all the time, keep in mind the 'definite purpose' label on motor contactors means defiantly not lighting.
I use them anyway in some cases, especially with a simple parking lot and 120V photo eye.
However I have countless hours troubleshooting loud and buzzing contactors...

I look for 'latching' type contactors for lighting panels for commercial offices / retail stores, GE/ABB is a good choice.
GE (now ABB) and others make a product called a CR 460 lighting contactor that has a 'latching relay' kit.
Another thing to keep in mind is your control voltage, we used to use allot of line voltage control like 120V,240V or 277, but now with the IoT 24VAC is more 'future proof' with all the PLC's and digital controllers people come up with.

my last comment is its often erroneously mentioned on here that industrial controls need to be listed, check with your AHJ, I have had to correct many, Article 409 control panels need only be approved not listed.
If I build a panel and sell it to another contractor I put a 508A sticker on it, but you as your own contractor building a panel yourself don't need any per the NEC 409.
Check your local ordinances/laws though YMMV
Please post a photo of the completed project for us.

 

[Todd0x1]

I do this all the time, keep in mind the 'definite purpose' label on motor contactors means defiantly not lighting.

WEG has some nice compact general purpose contactors that are UL Listed (vs recognized) I have been using those for various things with great success.

 

[jim dungar]

I do this all the time, keep in mind the 'definite purpose' label on motor contactors means defiantly not lighting.

Definite purpose contactors can definitely be used for switching lighting, but they have been feature and price optimized for resistive and motor locked rotor switching found in typical hacr and pumping applications.
Lighting contactors however, are often available in more the 4 pole version, some up to 12, they are available in mechanically held as well as electrically held versions, they usually have contacts that are designed to switch Tungsten Lamp and Fluorescent Ballast loads.

 

[kwired]

My first program had an output controlled by an internal timer which was triggered by a falling edge NO contact. Press button and when you let go of the button the output turns on and stays on for 5 seconds then turns off.

Been a little over 30 years ago now but when still in trade school one of first programs we did was one to control traffic intersection signals. Must have been first year instructor had this idea as we built a model intersection on a board, painted roadways and green grass, etc on the board and used little neon lights in the traffic lights.

One of first things we learned by trial and error was those little neon lights would not work on triac outputs without additional bleeder resistors as the triac leaked enough current when it was in "off state" the neon lights would still light up.

Besides that we started out with simple timing programs, and then added left turn signal, vehicle detection signals though they were simulated with simple switch instead of actual detection methods in the real world but this was more about programming than those detection methods, and even adding crosswalk lights and push to cross buttons.

Lab also had from previous years a setup with some augers, hopper bins, a weighing scale on one bin, and maybe a few other control devices or limits thrown in here and there. The material handled was some poly pellets that would get transferred from one bin to another and ultimately made it's way back to the first bin at some point. We would write different programs for different scenarios that the instructor would present us and then run through and see if we could make it work according to the needs of the scenario. Final stage that in a real situation would have been "unload for shipping" or similar simply transferred it back to the starting bin for reusing that material for another cycle.

 

[Bwas]

I usually use a contactor with an HOA switch and one photocell. HAND=lights on, OFF=lights off, AUTO=lights controlled by photocell. You could use PLC control instead of the photocell or in conjunction with the photocell, but that seems a little more complicated than is usually necessary.

 

[Todd0x1]

I usually use a contactor with an HOA switch and one photocell. HAND=lights on, OFF=lights off, AUTO=lights controlled by photocell. You could use PLC control instead of the photocell or in conjunction with the photocell, but that seems a little more complicated than is usually necessary.

I need some functions the PLC will make easy such as combine timeclock + photocell, include manual override that clears on next cycle (ex: pushbutton disables the lights but they turn on again the next day) but the main reason for looking at this was to use the PLC's ethernet to control remotely located contactors elsewhere on the property. The PLC and field I/O modules are substantially lest costly than the wire to run the lighting circuits (or even control circuits) all back to one place.

 

[Bwas]

What is the difference in the result of the calculations?

 

[Todd0x1]

What is the difference in the result of the calculations?

Cost difference? About $800 vs 600ft total length of new underground conduit, entering 4 buildings with it, and wire. Didn't even bother to price all that out.