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Solid State Relays (with a PLC) to control fluorescent lights instead of contactor

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    Solid State Relays (with a PLC) to control fluorescent lights instead of contactor

    I am pricing a new lighting job and the business is asking to have the lights controlled by a solid state relay and the end of each row instead of the contactor that I originally quoted. The relays would be controlled a PLC that they would provide along with the relays. I have never done this before and they are asking me if this will meet code requirements and I could find nothing in the 2011 book. I love the idea of controlling these lights like this but where can I verify this will meet code before inspection. The local inspector is not a sounding board.

    #2
    NEC does not address how to control your lights, the PLC control panel may need to be UL 508 listed. I am not a big fan of solid state relays as they are hard to troubleshoot. I don't know if they will work for this application, you should check to be sure or tell your client that you will just wire it up.

    By the way there is an Everett WA based company "PLC Multipoint" that makes turn key lighting control panels.
    Moderator-Washington State
    Ancora Imparo

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      #3
      IMO solid state is not the best idea for fluorescent lighting.
      Bob

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        #4
        Originally posted by petersonra View Post
        IMO solid state is not the best idea for fluorescent lighting.
        I guess that would depend on the min. current draw the relay needs to operate and the startup current draw of the ballast.

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          #5
          Originally posted by G._S._Ohm View Post
          I guess that would depend on the min. current draw the relay needs to operate and the startup current draw of the ballast.
          I did not say you could not make it work, you probably can. The fl. lights in my garage are on a solid state motion detector and they work adequately, although most of the time I have it turned off because when it is cold it sometimes will come on for no apparrent reason. I use the motion sensor mostly as an on/off switch.

          one of the nice things about using contactors is that you can turn a lot of lights on with a single contactor. I have seen people use 8 pole relays to turn on 8 banks of lights with a single contactor.

          solid state stuff tends to be a little flakier than dry contacts in my experience. but if someone wanted to do it that way, it would not bother me all that much to do what the paying customer wanted.
          Bob

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            #6
            The PLC would switch/control the electronic network of the relay not the lights,the lights would function via a contact on the relay,,,,,,,,,,,,,if I'm understanding the OP correctly.

            dick

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              #7
              Originally posted by dicklaxt View Post
              The PLC would switch/control the electronic network of the relay not the lights,the lights would function via a contact on the relay,,,,,,,,,,,,,if I'm understanding the OP correctly.

              dick
              I am pricing a new lighting job and the business is asking to have the lights controlled by a solid state relay and the end of each row instead of the contactor that I originally quoted.
              I will admit he phrased the OP so that it is hard to tell for sure just what he means. I took it as directly controlling the lighting from a SS relay.

              It seems uncontroversial to ask if it OK to control a contactor from a SS relay as that is very common.
              Bob

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                #8
                If the customer wants to spring for the tab he can get a PLC with relay cards,then just have a number of digital dry contact outputs as required to turn the lights on and off as needed.It could be programmed a multitude of different ways.

                dick

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                  #9
                  Originally posted by grapeape View Post
                  I am pricing a new lighting job and the business is asking to have the lights controlled by a solid state relay and the end of each row instead of the contactor that I originally quoted. The relays would be controlled a PLC that they would provide along with the relays. I have never done this before and they are asking me if this will meet code requirements and I could find nothing in the 2011 book. I love the idea of controlling these lights like this but where can I verify this will meet code before inspection. The local inspector is not a sounding board.
                  I guess your question is if you can turn on a group of fluorescent ballasts with a SS contactor. It should be no problem, just have to follow the other sections of the Code, such as circuit breaker loading and housing the SS contactor in a proper enclosure.

                  Comment


                    #10
                    Originally posted by weressl View Post
                    I guess your question is if you can turn on a group of fluorescent ballasts with a SS contactor. It should be no problem, just have to follow the other sections of the Code, such as circuit breaker loading and housing the SS contactor in a proper enclosure.
                    There are optically coupled SSRs which provide hard isolation between power and control side. The optical trigger can operate on logic level power, maybe 15mA or so.

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