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    Transformer Monitoring Installation

    A customer requires power monitoring at the secondary of the following transformer:
    KVA: 1000
    Primary Volts: 13200 VAC
    Primary Current: 43.7
    Secondary Volts: 480Y/277
    Secondary Amps: 1203

    Proposed installation has the monitoring device mounted on a wall @ 8' away, total lead length @ 12', CT leads and voltage leads in separate conduits. Monitoring equipment voltage leads terminate at a disconnect/fuse holder with FNQ-R-5 fuses. SCCR rating is "Exempt Per UL-508A Paragraph 49.5".

    I've read 240.21(C) and don't see how this could be compliant. Most of the monitoring equipment I'm familiar with is entirely enclosed in switchgear as mentioned in the article.

    If I'm referencing the wrong article, please direct me where to find the correct reference to determine placement of OC/Short Circuit protection and conductor size, if it's even possible.




    #2
    Duplicate
    Ron

    Comment


      #3
      Is your concern that the voltage sensing leads are not protected? We typically mandate that the fuse protection you mention occurs within the 10' lead length of the transformer secondary terminations per 240.21(C)(2)(1) exception.
      Or is your concern the lack of short circuit ratings?
      Ron

      Comment


        #4
        My concern is the #10 leads attached to the secondary bus leaving the transformer enclosure unprotected. Code based size and placement of fuses is what I'm looking for.

        Comment


          #5
          Originally posted by 110.14(D) View Post
          My concern is the #10 leads attached to the secondary bus leaving the transformer enclosure unprotected. Code based size and placement of fuses is what I'm looking for.
          240.21(C)(2)(1) exception gets you 10' lead length
          Ron

          Comment


            #6
            IMO this is a class 1 circuit.

            725.3 Other Articles. Circuits and equipment shall comply
            with the articles or sections listed in 725.3(A) through (N).
            Only those sections of Article 300 referenced in this article
            shall apply to Class 1, Class 2, and Class 3 circuits.
            Article 240 is not mentioned in 725.3 (A) thru (N).

            Take a look at 725.45.
            Bob

            Comment


              #7
              Originally posted by ron View Post

              240.21(C)(2)(1) exception gets you 10' lead length
              Exception: Where listed equipment, such as a surge protective device(s) [SPD(s)], is provided with specific instructions on minimum conductor sizing, the ampacity of the tap conductors
              supplying that equipment shall be permitted to be determined based on the manufacturer’s instructions.



              Looks like the exception is dependent upon the manufacturer's instructions which unfortunately don't specify protection size, placement, or conductor ampacity, so it may not help us here.

              240.21(C)(2) requires compliance with (1), (2), (3), and (4). Seems like (1), (2), (3) are in place and I'll find the size of the primary OCPD rating tommorow to do the calculation described in (4).

              Comment


                #8
                Originally posted by petersonra View Post
                IMO this is a class 1 circuit.



                Article 240 is not mentioned in 725.3 (A) thru (N).

                Take a look at 725.45.
                725.2 Definition of Class 1 Circuit:

                Class 1 Circuit. The portion of the wiring system between the
                load side of the overcurrent device or power-limited supply and
                the connected equipment.

                At this time I don't have an overcurrent device at the point of supply.


                Comment


                  #9
                  Originally posted by 110.14(D) View Post

                  725.2 Definition of Class 1 Circuit:

                  Class 1 Circuit. The portion of the wiring system between the
                  load side of the overcurrent device or power-limited supply and
                  the connected equipment.

                  At this time I don't have an overcurrent device at the point of supply.

                  Where does it say anything about point of supply. It says load side of oc device.
                  Bob

                  Comment


                    #10
                    There is no oc device, #10's connected directly to 1203 amp secondary.

                    Comment


                      #11
                      Originally posted by 110.14(D) View Post
                      A customer requires power monitoring at the secondary of the following transformer:
                      KVA: 1000
                      Primary Volts: 13200 VAC
                      Primary Current: 43.7
                      Secondary Volts: 480Y/277
                      Secondary Amps: 1203

                      Proposed installation has the monitoring device mounted on a wall @ 8' away, total lead length @ 12', CT leads and voltage leads in separate conduits. Monitoring equipment voltage leads terminate at a disconnect/fuse holder with FNQ-R-5 fuses. SCCR rating is "Exempt Per UL-508A Paragraph 49.5".

                      I've read 240.21(C) and don't see how this could be compliant. Most of the monitoring equipment I'm familiar with is entirely enclosed in switchgear as mentioned in the article.

                      If I'm referencing the wrong article, please direct me where to find the correct reference to determine placement of OC/Short Circuit protection and conductor size, if it's even possible.


                      Is there are reason they want to mount it on the wall? There should be a panel on the transformer designed to hold the optional monitoring equipment. We install a lot of Powerlogic monitors, the CM2350 should do everything you need to do and has protection built into the unit.

                      Comment


                        #12
                        Yes Zog that would have been ideal, didn't happen that way. I don't know why it has to be where it is, I have no influence over how any of this gets done.

                        Anyway, back to 240.21(C)(2)(4).

                        As long as we've come this far, just to satisfy my personal curiosity, according to the described formula this would this be the required ampacity of an unprotected secondary?

                        OCPD setting based on ABB current relay with tap pins in position 6 x INST.(X TAP) dial set at 14.

                        (OCPD Setting x (Primary Voltage/Secondary))/10
                        (84 x (13200/480)) / 10 =
                        (84 x 27.5) / 10 =
                        2310 / 10 = 231 Amps
                        Last edited by 110.14(D); 10-18-19, 09:44 PM.

                        Comment


                          #13
                          Originally posted by 110.14(D) View Post
                          Anyway, back to 240.21(C)(2)(4).

                          As long as we've come this far, just to satisfy my personal curiosity, according to the described formula this would this be the required ampacity of an unprotected secondary?

                          OCPD setting based on ABB current relay with tap pins in position 6 x INST.(X TAP) dial set at 14.
                          The the rating of the overcurrent device protecting the primary of the transformer would be the 51 relay. The value you were calculating with above; was it the 50 relay or 51 relay setting?
                          Was the 51 setting at 84A or the 50 setting at 84A? Since the FLA of the primary was 43.7A, I'm not sure if the 51 setting would be as high as 84A.
                          Ron

                          Comment


                            #14
                            That would be a model 51I. Not being familiar with the device I downloaded the manual. Works out to @192% which table 450.3(a) seems to allow. Impedance is 5.79 in supervised location.
                            Last edited by 110.14(D); 10-19-19, 10:37 PM.

                            Comment

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