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cable guidance UL508A, NFPA70, NFPA79

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    cable guidance UL508A, NFPA70, NFPA79

    What are the cable requirement that is going from a frequency driver to the motor according to NFPA70.
    Compared to NFPA79 is there additional requirement.

    So far I understand that a cord to the panel could be of the following types according to UL508A.
    28.5.3 The cord shall comply with the Standard for Flexible Cords and Cables, UL 62, and be one of the
    following types: S, SE, SEO, SEOO, SJ, SJE, SJEO, SJEOO, SJO, SJOO, SJT, SJTO, SJTOO, SO,
    SOO, ST, STO, STOO, or portable power cable type G, PPE, or W power cable.

    But I do not understand what is the requirement for the cable between driver ant the motor in NFPA70 and what is additional required if NFPA79 applies.
    I have tried to read the NFPA70 and if I am thinking right those hard service cord cables could be used.
    In NFPA79 is it forced that it must be a conduit where the cables goes within or is it any cable that is strong enough to not be placed in an conduit according to clause?




    #2
    We are going to need to know more about the specific installation.

    In general the NEC does not allow cords to be used for permanent wiring. There are exceptions to that for certain applications need of movement etc.

    The other issue is we need more info to determine which standards apply to this project.

    Comment


      #3
      Originally posted by larsahl View Post
      What are the cable requirement that is going from a frequency driver to the motor according to NFPA70.
      Compared to NFPA79 is there additional requirement.

      So far I understand that a cord to the panel could be of the following types according to UL508A.
      28.5.3 The cord shall comply with the Standard for Flexible Cords and Cables, UL 62, and be one of the
      following types: S, SE, SEO, SEOO, SJ, SJE, SJEO, SJEOO, SJO, SJOO, SJT, SJTO, SJTOO, SO,
      SOO, ST, STO, STOO, or portable power cable type G, PPE, or W power cable.

      But I do not understand what is the requirement for the cable between driver ant the motor in NFPA70 and what is additional required if NFPA79 applies.
      I have tried to read the NFPA70 and if I am thinking right those hard service cord cables could be used.
      In NFPA79 is it forced that it must be a conduit where the cables goes within or is it any cable that is strong enough to not be placed in an conduit according to clause?



      In general, UL508a does not cover the cabling between the VFD and the motor. The scope of UL508a stops at the field terminals. However, if you want to you can permanently connect power or field devices to the control panel you can do it via the provisions of 28.5. This is only allowed for portable equipment.

      The NEC only requires that you follow the normal rules in article 430. If you want to connect it up with cord there are cases where this is allowed but there are rules to be followed in article 400. There is considerable dislike of cord connections by some on this forum, but real world experience suggests they generally work just fine if not in a situation where they are likely to be damaged and in some cases they work a lot better than conduit or other raceways.

      The instructions that come with the VFD will likely tell you what to use to hook it up. Most of the time these days it will suggest VFD cables but also allow for normal building wire. Interestingly, despite it being commonly used in such applications, I don't ever recall seeing a VFD manual that says you can use cord of any type.
      Bob

      Comment


        #4
        Originally posted by petersonra View Post
        There is considerable dislike of cord connections by some on this forum, but real world experience suggests they generally work just fine if not in a situation where they are likely to be damaged and in some cases they work a lot better than conduit or other raceways. .
        Real world experience also tells me the NEC dislikes cord as do inspectors and fire departments.

        But that is why I am asking what the application is, the NEC may have nothing to do with it and therefore cord would not be a problem.

        Comment


          #5
          The NFPA is concerned about starting fires, not really about proper functionality or longevity. UL is mostly the same, but backed up by testing, however as mentioned their interest will stop at the load terminals.

          This is more of an "RTFM" issue. Flexible cord on the output side of a VFD that is NOT shielded is a huge risk of creating a nice local FM radio transmitting antenna that will bleed RFI/EMI all over everything in your facility. You need to use shielded VFD cable, with the shield grounded at BOTH ends, or use building wire with XLPE insulation in STEEL conduit. Most VFD mfrs are now warning against using THHN, because the PVC insulation can break down too soon under the voltage stresses of the PWM output causing Corona Discharge under the right circumstances. RHH/RHW is the preferred cable type. If the output must be flexible, you can get shielded flexible VFD cable for that purpose, I strongly suggest doing that. None of the above is even mentioned in anything by the NFPA or UL, not their thing...

          Download and read this, cover to cover. It's not really specific to Allen Bradley drives (until the very end), the principles it discusses apply to ALL VFD installations.
          http://literature.rockwellautomation...n001_-en-p.pdf


          (RTFM: Read The "Factory" Manual)
          __________________________________________________ ____________________________
          Many people are shocked when they discover I am not a good electrician...

          I'm in California, ergo I am still stuck on the 2014 NEC... We'll get around to the 2017 code in around 2021.

          Comment


            #6
            There is a electrical cabinet and a frame. The motor sitting on the frame.
            The complete frame is movable with the cabinet on it. The cable that goes from the cabinet to the motor is fixed installed. Another motor is not fixed installed, it is connected by plug to the electrical cabinet due to it is an optional motor.

            In the manual for the VFD they are speaking of TC-ER cable that are shielded.
            http://www.belden.com/techdatas/metric/29507.pdf

            I am thinking about using a SOOW shielded cable with 85% of braid for both motors.

            Comment


              #7
              Originally posted by larsahl View Post
              There is a electrical cabinet and a frame. The motor sitting on the frame.
              The complete frame is movable with the cabinet on it. The cable that goes from the cabinet to the motor is fixed installed. Another motor is not fixed installed, it is connected by plug to the electrical cabinet due to it is an optional motor.

              In the manual for the VFD they are speaking of TC-ER cable that are shielded.
              http://www.belden.com/techdatas/metric/29507.pdf

              I am thinking about using a SOOW shielded cable with 85% of braid for both motors.
              You referenced UL508a requirements previously. If you are listing this cabinet you have to follow the rules. If the instructions that come with the VFD require you to use a certain kind of cable you have to do so. However, I would read very closely what the manual actually says and not infer anything. It may be that the cable they mention is more like a suggestion than a requirement. personally, if it was me, I would run EMT or rigid and regular wire for the fixed motor.

              Is the non-fixed motor on a VFD? If so, I would be inclined to run it with VFD cable. Keep in mind even if you use TC-ER cable, it still needs to be supported all the way to the motor. It can't just hang. I piece of strut works well for such things.
              Bob

              Comment


                #8
                The cable in the manual is just an example/suggestion for a cable to be used.
                This is from the manual:
                "
                A variety of cable types are acceptable for drive installations. For many
                installations, unshielded cable is adequate, provided it can be separated
                from sensitive circuits."

                The optional motor with the connection plug in one end and fixed at the motor end is also sitting on the frame. The cable length is just 1 meter from enclosure to the motor. Coming out from the enclosure side up to the motor and actually I was thinking about just leave it as that with no cable support because the distance is short and the motor shall be able to dismount and detach if you want to remove that optional motor. I am looking at a shielded SOOW cable with 85 % braid to be used for this optional motor.
                I am also thinking about using the same for the fixed installed motor. So I am unsure if that is the correct one to use according to NEC430.

                Comment

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