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Thread: Class 1,2, 3 power supplies

  1. #1
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    Class 1,2, 3 power supplies

    Article 725 mentions a circuit card being listed as a Class 2 power source. Are there any PLC power supplies or analog output cards that are listed as being Class 2 power sources?

  2. #2
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    Its specific per manufacturer. The PLCs I work on (AB) use external power supplies and you just need a class 2 supply. AB has some very good technical literature on this. I will move your post to our new automation topic
    Moderator-Washington State
    Ancora Imparo

  3. #3
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    Generally the 24 Vdc supply in that environment is over the VA rating for class 2, could easily be over by a factor of 10. It is running so much stuff.

    What you can do is take the output of the 24Vdc supply and run it through something like a Puls device that will take the input and give you CL2 rated output with electronic tripping and a red led that lights up if the output tripped.

    Then you could take the CL2 output of the Puls device and feed the output card bus (or input card bus) and your field wiring will be CL2 compliant.

    https://www.pulspower.com/us/product.../pisa11class2/
    Lasciate ogne speranza, voi ch'intrate

  4. #4
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    I didn't state what I was looking for very clearly. If the PLC power supply and analog output card are not rated as a Class 2 power source and the analog outputs are loop powered the field wiring cable will need 600 volt insulation for a Class 1 circuit and I can't use PLTC.

  5. #5
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    Depends what you want to do. If the combined load of the outputs of the card are under the CL2 power limits, you can convert the outputs to a CL2 wiring method by using an upstream device, CL2 listed power supply or CL2 listed protective device like the Puls, that gives you a CL2 compliant source.

    In this case the rating of the card will not matter. It's a CL2 circuit if the upstream power source is CL2 and you can feed the output card bus with it.

    On the input side this would be common because the input devices can operate on low power and the field input devices may be manufactured to expect a CL2 wiring method. On the output side, depends on how much power you need to drive the load. CL2 is possible at the output side also.
    Lasciate ogne speranza, voi ch'intrate

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