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Ungrounded 480x240 delta to delta 3ph 3w voltage to ground reading

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    Ungrounded 480x240 delta to delta 3ph 3w voltage to ground reading

    Need clarification / conformation on the voltage readings to ground, and suggestions / solutions.

    Knowing the secondary 240 line to line should be 240v and line to ground should be 0v.
    Found a voltage reading to ground on a disconnect and was able to determine the circuit that was causing the fault.
    Removed the wiring from both the disconnect and wiring to the circuit breaker at the panel board and locked out both. Have not been able to troubleshoot further at this time.

    Now another disconnect is reading to ground. I am not able to secure this circuit, and know this needs to be addressed before another fault may occur. Can someone explain what may occur if this is not repaired or resolved.

    The location has an old CH V48M24T12F is a Delta to Delta transformer. Eaton’s tech support sent me this “Since this transformer does not create a neutral there is nothing to ground and the 240 VAC does not have a reference to ground and you should not see voltage to ground, only line to line.”

    I am suggesting the ungrounded transformer be replaced with a grounded system.

    Thank you,
    Robert

    #2
    Just to clarify:
    The secondary is 240D, ungrounded?

    If it is, then this is not right:
    “Since this transformer does not create a neutral there is nothing to ground and the 240 VAC does not have a reference to ground and you should not see voltage to ground, only line to line.”
    Without data you’re just another person with an opinion – Edwards Deming

    Comment


      #3
      yes that is correct only, there is only a ground bolt to the case inside the transformer nothing to the windings

      Comment


        #4
        Originally posted by killer76 View Post
        yes that is correct only, there is only a ground bolt to the case inside the transformer nothing to the windings
        Since the 240D is ungrounded, then the phase to ground voltage is undefined. It can be about anything (between 240V and 0V). One can usually measure something because of capacitive coupling. If the coupling is perfect balanced, the phase to ground voltage would be 139V = 240/(sqrt(3)

        If you are reading phase to ground of:
        240V
        240V
        0V
        that is telling you that you one phase has an unintentional ground.

        Before I suggested changing to a grounded system, suggest checking why the existing is ungrounded, and the requirement of the existing loads. Some loads may not be happy with some types of grounded systems.
        Without data you’re just another person with an opinion – Edwards Deming

        Comment


          #5
          Originally posted by killer76 View Post
          yes that is correct only, there is only a ground bolt to the case inside the transformer nothing to the windings
          There should be ground detectors - Could be as little as three incandescing light bulbs.
          Without data you’re just another person with an opinion – Edwards Deming

          Comment


            #6
            the only loads are to single phase and three phase receptacles for welding machines and a couple plasma cutters, fused disconnects feed the receptacles.

            going to get the measurements from the disconnects when no load in present.

            Comment


              #7
              was told that using digital volt meter will give different readings compared to the wiggy type meter, i have an Ideal Vol-Con tester and digital UEI and will use both.
              I was asked to see if you can you give a little more on the ground detectors - Could be as little as three incandescence light bulbs. How would they be connected
              any advice or suggestions are greatly appreciated

              Comment


                #8
                Ive seen systems as simple as lights connected in series between phases and ground or you can get more "professional"
                http://www.directindustry.com/prod/e...3-1690990.html
                At my age, I'm accustomed to restaurants asking me to pay in advance, but now my bank has started sending me their calendar one month at a time.

                Comment


                  #9
                  Originally posted by killer76 View Post
                  was told that using digital volt meter will give different readings compared to the wiggy type meter, i have an Ideal Vol-Con tester and digital UEI and will use both.
                  I was asked to see if you can you give a little more on the ground detectors - Could be as little as three incandescence light bulbs. How would they be connected
                  any advice or suggestions are greatly appreciated
                  The vol con will be more likely to give you "0" volts (if there is not a fault) and more useful information.
                  Ethan Brush - East West Electric. NY, WA. MA

                  "You can't generalize"

                  Comment


                    #10
                    Originally posted by killer76 View Post
                    ... I was asked to see if you can you give a little more on the ground detectors - ...
                    Code section is 2017 NEC 250.21.B Also suggest reading 250.21.A and 250.21.C.

                    This is not a design. It is missing minor things like fuses.

                    If 240V incandescent bulbs are not available, 240V transformered pilots also work.

                    the worm
                    Attached Files
                    Without data you’re just another person with an opinion – Edwards Deming

                    Comment


                      #11
                      Just to clarify, in a 240V 3 phase delta system, you must have ground fault monitoring, OR you must have a grounded phase, a.k.a. "corner grounded", in which case one of the phases will measure zero V to ground, the other two will measure 240V to ground and all 3 will measure 240V phase to phase. A 3 phase delta system without one or the other is a code violation.
                      __________________________________________________ ____________________________
                      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


                        #12
                        that is correct. no corner ground, and no monitors.
                        additional issues, in this application

                        400A MAIN City Supply to 600A 480V 3Ph MLO panelboard, 150A, 480V 3P [should be 175A]
                        to 112.5kva 480v 3ph D x 240v 3ph D 3W to (no secondary OCP 240.4 (F) indicates delta-delta 3-wire shall not be considered)
                        42CKT 225A 240V MLO load center w/
                        6) 50A 3p left side (third cb removed first leg on 3p failed)
                        5) 50A 3p & (1) 30A 3p right side
                        load center is over loaded, the phases are not balanced due to the usage of single-phase welders. one other has failed on one leg have not confirmed what phase
                        both are locked out,
                        all breakers are feeding 60A fused disconnects w/ 60A fuses all for welding machines, some of the disconnect have (3) twist lock receptacles (1) 50A 3ph & (2) 30A 1ph.
                        the twist locks are showing sign of burning at the prong opening

                        suggest replace the Delta xfmr with wye or add detectors to code, increase size to support load
                        suggest add individual fused disconnect w/ correct fusing & receptacles for each welder. client does not want hard wire they will use extension cords of various lengths, another concern.
                        any additional suggestions would be great.

                        Thanks

                        Comment


                          #13
                          I would look at the load again first and then try to figure out the best way to feed it..You can corner ground the delta secondary of the existing transformer and this should give you functionality for OCPD operation, for other leg faults to ground. That is necessary imo, compared to monitoring the existing floating system for faults and then expecting to have someone available to manually clear faults when the detector gives abnormal reading. Not likely and not a scenario I would lean into. Guys today will just keep running it until the breaker or fuse trips, then try resetting the breaker or replacing fuses to get it running again.

                          Converting to all solidly grounded system I would look for. But that is load dependent. You have to look at the load including maybe consulting with the welding machines manufacturer to see what they prefer as a source.

                          Possibly the supply was a much older existing installation and the new loads were simply added on to what was available. You want to know if 240 delta, floating or grounded, is necessary for the machines that are there now. Really an unknown at this point. I would guess the 112kVA floating 240 delta secondary dates from an earlier era than the present load. Is it necessary or can it run on the utility 480 V supply.

                          The welding machines are possibly dual voltage at the input, 480 or 240 with adjustable taps would be common. If so, I would have an eye on moving the load to the utility transformer. But first I would check that transformer to see what it is, grounded and probably Y, but I would check it and recheck it.

                          The welding machine manufacturer may have a preference for an isolating transformer, or not. Only they know this answer. If the machines can run on the 480 V supply, I would probably be interested in moving the load there.

                          Make sure you have good EGC grounding attachment to everything.

                          Replace the twistlok devices that show signs of burning and maybe wring it out for faults. If they are continuous production machines, running big welders on cords and twistloks is going to take a beating.

                          I would not consider monitoring over solid grounding, if I felt there was no one who really understood the system and could troubleshoot it safely, a ghostbuster.



                          Lasciate ogne speranza, voi ch'intrate

                          Comment


                            #14
                            I have been told replacing fuses and resetting the breaker is normal, the new issue is one leg at the disconnect has no voltage, and the breakers are starting to fail.

                            I believe the breakers are failing due to (3) receptacles from one disconnect(s) and unbalanced phase's

                            I need a better understanding of 630.11 to be safe I go with the 100%, for (B) group welders even more confused. I found an old section from NEC2005 the show a diagram of several welders fed by one disconnect, would think if it’s not in 2017 then something is different
                            630.12 OCP shall be provided in 630.12 (A) & (B) not more than 200%, If anyone can provide further explanation maybe a sketch that would be great, then 630.13 indicates a switch or circuit breaker for each welder.

                            only one of the welders has integral cb other than this one shouldn't all of the others comply with 630.13 or is the method described in 630.11 and 630.12 permit multiple welders to one disconnect.

                            I have gone with manufactures installation in the manual. It states each welder has disconnect, conductor size, fuse requirements, along with max. distance from panelboard.

                            Most of the welders are 230 / 460 single & three phase, only about three are 230 single phase.

                            the 600A 480V 3Ph panelboard has 200A fused disconnect w/ 125A fuses hard wired to the buss to a another 200A fused disconnect w/ 125A fuses to the other end of the facility. this is supplying a 125A 480V 3Ph (6) ckt panelboard for (6) welders (2) 15A 3p, (2) 25A 2p, (1) 35A 3p, (1) 20A 3p.

                            In the 600A panel some breakers are spare, and several 2p are to lighting some 3p only using 2 legs, would rather use the 150A 480V 3p and run to another small panel closer to the welding location.

                            Thank you for your feedback


                            Comment


                              #15
                              Originally posted by killer76 View Post
                              I have been told replacing fuses and resetting the breaker is normal, the new issue is one leg at the disconnect has no voltage, and the breakers are starting to fail.

                              I believe the breakers are failing due to (3) receptacles from one disconnect(s) and unbalanced phase's



                              Most of the welders are 230 / 460 single & three phase, only about three are 230 single phase.



                              Thank you for your feedback

                              If you are blowing fuses and breakers anywhere on the ungrounded 240 V delta, it means you normally operate every day with faults to ground on the floating delta and the fuses only blow for the second ground fault (so it's actually a line to line fault through two shorts in series). It burns in two places and has line to line fault current available.

                              You are not a candidate to safely retain and operate the ungrounded system. You should blow no fuses on a floating system, but clear the first fault quickly and permanently, before the second fault happens.. That is the design intent of the industrial floating secondary.

                              Breakers are failing from repeated resetting, or they may actually be doing their job. Change the burned out breakers.

                              What type of welders, what duty cycle. Are the welders used in the production process or are they just there to repair the plant.

                              If the welders are just there to repair the plant, you probably don't use more than one at the same time in the same spot. Load calc is for the actual load. I would say you can have as many welder outlets on a circuit as you want if you are only going to plug in and operate one welder at a time. Load is added to the circuit by the use of the welders (since it is manual only).

                              If you use the welders in the production process, that load calc is completely different and I probably would not want to derate too much.

                              I am thinking the portable plant repair welders, design wise, I would want to see it on 480 as much as possible. Even then the cords and outlets are going to be heavy to lug around.

                              If most of the heavy load and special use industrial equipment can be moved to the utility 480, dual voltage rated equipment, I would consider that as a path forward, with an eye on reducing the load on the 112 kVA 240 delta secondary so much, that that dog can be retired. If I could get the remaining load under 30 kVA, I would like that, and plan on eliminating the 240 delta transformer, refeeding the load with a grounded Y secondary.

                              So survey it first to see if the 240 delta can be retired and most of it's load moved to the utility 480. Check that service to make sure it does not have the same problems. Refeed the rest if it's under 30 kVA remaining.

                              If you still have a lot of load for the 240 delta. Most likely I would try to retain it with a corner grounded secondary and new panels and breakers for it.

                              They need to spend some money sounds like. Put the plan together first.

                              Key issue seems to be how much load do you really need to put on the existing 240 delta. There may be nothing wrong with the transformer if you actually have the right or necessary load for it. If you don't really have more than 30 kW of load, it's a dog, especially if you can (benefit from) a move the welders to 480.
                              Lasciate ogne speranza, voi ch'intrate

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