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    #31
    Originally posted by kwired View Post
    I can agree with that, what might be dangerous though is not having any EGC system - which from OP's descriptions so far doesn't appear to be any.

    If this were originally a grounded phase system, then as old as it is, should have been legal to run just three conductors to separate buildings and then ground at each building like you would have grounded a service. Today you can't do that anymore. But don't sound like anything is grounded period, and no ground fault indication either.
    Maybe, it's just not really clear....he said "local grounds" only......I don't know if he is talking system grounding or equipment grounding or bonding. If it's old, it's probably all in rgs.
    Ethan Brush - East West Electric. NY, WA. MA

    "You can't generalize"

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      #32
      OP really needs to get an EE in there familiar with his type of distribution. I think he was headed that way. It may be an old EE with a belt and suspenders.
      Tom
      TBLO

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        #33
        Originally posted by ptonsparky View Post
        OP really needs to get an EE in there familiar with his type of distribution. I think he was headed that way. It may be an old EE with a belt and suspenders.
        Or a competent electrician.....
        Ethan Brush - East West Electric. NY, WA. MA

        "You can't generalize"

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          #34
          If he has all RGS conduit feeders, all steel boxes, and proper attention was paid to the system so that all the site metal with electrical power to it is bonded to the contiguous EGC system, the hazard would be greatly reduced. The floating ungrounded supply would still be legal with signage and GF detection.

          We would say he has 3 phase 3 wire with 4 conductors.

          With multiple buildings spread out over a site dating to 1935, you have to assume, of all the guys who worked on the power there, some of them should not be touching wiring except with sufficient supervision. Not a bet I would take.

          Even if he has a lot of visible RGS, you really won't know if all the loads and structures are connected to it without a survey. Knowing this is in the future.

          3 phase 3 wire 3 conductors using local "Peg Grounding" has been installed enough times that it shows up in MSHA fatal accident investigation reports. These were not installed by mistake. It is a system that was repeated. Then lots of guys will come along and just copy something because ... that's the way it has always been done. Or that's the way we do it here ...

          According to accident reports, operators have tried to use earth as their safety grounding system. When this has been done, fatalities have normally been the end result. The following accident report details the hazards of using earth as a safety grounding system.

          https://arlweb.msha.gov/S&HINFO/TECHRPT/GROUND/MNMELECT.HTM

          In the modern times, all the guys will just guess or assume the breaker will trip if there is a problem. They will wait for the breaker to trip. And if the breaker resets, they will assume the problem is gone. These guys are not ghostbusters.

          One I found is exactly what the OP describes. I don't know if he has local only grounds or RGS. Site I saw had two large (old old old) industrial building complexes and then three sites in the mine with 480, mostly 3 phase 3 wire 3 conductors. Main transformer was floating Y with three conductors leaving.

          One of the mine power site was a floating 20 hp dewatering pump. There was a mix of 4 conductor SO, EMT, but the underground feeder was 3 conductors. Any fault and all the metal would go to 277.

          This site had passed many MSHA required annual grounding inspections. How I don't know, but it took me all of five minutes to fail it.

          In a large site feeding a load 1000 ft away underground, installed cheap way way back, do you think they ran RGS. Point is, you will not know the answer until you survey it. And you have to know what you are looking for.

          You have to verify your distribution system has an "effective fault clearing path back to the source".
          Last edited by __dan; 08-06-18, 05:30 PM.
          Lasciate ogne speranza, voi ch'intrate

          Comment


            #35
            To late to the debate, but I too wonder if the there is a grounded or grounding conductor missing to the source.

            Technically it is possible in such a case for everything in the building to behave like an ungrounded delta for a phase fault, but have 277 volts to remote earth. Such a system is dangerous because the ground current between the building and substation can result in fire or electrocution.
            Our comedian shamelessly joked about a blackout. Talk about dark humor.

            Comment


              #36
              Originally posted by Bretzel View Post
              Are you certain this is a wye system? What (if any of the source) conductors are grounded?

              The primary is 13,200 Wye, the secondary is 480 Wye. (Switchable to 600, 575, 535, 480, 460, 230 with the turn of a bakelite knob.) The primary is grounded at the transformers but the secondary is not and appears never to have been grounded. The entire distribution system is three wire. The older (1920s patent dates) oil-filled transformers are a mix of single and three phase installtions with local grounds to earth. This construction appears to be original. Newer dry transformers are installed in a similar manor. There is a mix of Wye and Delta transformers on the system.

              We have a number of ancient line surge arresters which appear to be of the carbon-filled ceramic canister type. I have to assume these require at least periodic maintenance or replacement. If one of them had a lightning strike at some point it could easily be the source of our ground fault.

              Apparently, no one knows exactly when the voltage issues arose but with the addition of some newer equipment with PLC and VFD controls it has become much more obvious.

              My plan at this point: While I find a consulting electrical engineer to bring in, I'll have my electricians start checking the grounding of the newer transformers and downstream equipment working backward in installation time looking for the lower voltage leg to be grounded at some location. We'll also check the very few underground runs we have for ground faults.
              Can you post pictures or the substation and transformers?
              Our comedian shamelessly joked about a blackout. Talk about dark humor.

              Comment


                #37
                Really interesting conversation (photos, too, please).

                It does sound like a shutdown for testing would he useful; it's also an excellent opportunity to make some new "as-built" drawings of the transformers/switchboards/etc (complete with more photos ).

                Comment


                  #38
                  Unfortunately, due to the nature of our work, cameras of any kind are not allowed on the property. It's a check your cell phone at the gate kind of place. Otherwise is a really cool operating museum!
                  Last edited by Bretzel; 08-06-18, 10:18 PM.

                  Comment


                    #39
                    Thank you to all who have added to this thread, it has been most informative. A special tip of my hat to Wire-Smith for the link to the GE transformer theory paper. I learned a lot and cured my insomnia at least 7 times this weekend! Really, it was very good information.

                    I have visually verified this is a 3 wire, no ground/neutral wire downstream of the primaries on the substation transformers.

                    At one time, we had our own seasonal hydro generating station and a small coal fired boiler which ran the generator during the dry season. It appears to have produced 600 DC which ran a motor-alternator to turn out the 480 at 60Hz. The motor-alternator would have been easier to regulate the frequency than would the hydro or stream.

                    The POCO supplies primary at 13,200. Each of three, 999,999 Watt transformer has two terminals on the top. One ties to a hot leg of the primary and one ties to a common with which is both bonded to the POCO ground and to a ground peg just outside of the building housing the transformers.

                    The 480 secondary side of the transformers has only two terminals. There are only three wires leaving the transformer building. T1 connects across leg A and B of the 3 plant distribution wires; T2 connects across leg B and C; T3 connects across legs C and A. There is a stud welded to the bottom of the side of each transformer can. This stud connects to a conductor which bonds each can to the next and then to the same ground peg as the primary. There is no distribution ground or neutral wire from here downstream.


                    The distribution is mainly on poles and cross arms, open wire. There are three locations with piped, underground wiring. Some more recent main installations have used 4 wire runs which are grounded to earth at each end but do not run all the way back to the transformer building. In these and all other areas of the plant there is a ground peg at each transformer, transformer bank, or machine. I understand these local ground pegs and earth cannot return a fault back to the source if we have an unintentional ground fault of one of the distribution legs. It appears the location of this fault is what we are now searching to find. There are no indicator lights on the system for faults. Through planned outages, we have found an area when we believe the ground fault has most likely occurred. The electricians are working the area de-energized. They are using a megger where appropriate and an ohm meter where necessary such as the arresters.

                    I have initiated discussions with business management to replace the transformers with a package substation with remote primary and secondary switching and proper distribution. I'm still looking for that EE who is knowledgeable, thorough, and old enough to have seen something like it before and who is reasonable enough to help plan a measured, staged conversion to a modern system.

                    Comment


                      #40
                      Originally posted by electrofelon View Post
                      Maybe, it's just not really clear....he said "local grounds" only......I don't know if he is talking system grounding or equipment grounding or bonding. If it's old, it's probably all in rgs.
                      I was going to reply to this, but looks like OP clarified some in last post. Appears to be an ungrounded system (at least the 480 volt system is) and is grounding done "locally" at each building? But likely only to non current carrying components leaving the system still ungrounded.

                      Can make for a real mess with stray currents when you have a ground fault on phase A in one building, a fault on phase B in another building and a fault on phase C in a third building.
                      I live for today, I'm just a day behind.

                      Comment


                        #41
                        Originally posted by kwired View Post
                        I was going to reply to this, but looks like OP clarified some in last post. Appears to be an ungrounded system (at least the 480 volt system is) and is grounding done "locally" at each building? But likely only to non current carrying components leaving the system still ungrounded.

                        Can make for a real mess with stray currents when you have a ground fault on phase A in one building, a fault on phase B in another building and a fault on phase C in a third building.
                        Yes I agree different faults in different buildings can be a mess when there is only a high impedance path between them
                        Ethan Brush - East West Electric. NY, WA. MA

                        "You can't generalize"

                        Comment


                          #42
                          So, it appears from the comments, clearing the present fault will make the system slightly safer but not safe. Correct?

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                            #43
                            Originally posted by Bretzel View Post
                            So, it appears from the comments, clearing the present fault will make the system slightly safer but not safe. Correct?
                            Correct. The system needs an EGC and ground detector lights.
                            Our comedian shamelessly joked about a blackout. Talk about dark humor.

                            Comment


                              #44
                              Originally posted by mbrooke View Post
                              Correct. The system needs an EGC and ground detector lights.
                              Or intentionally ground one of the conductors.

                              Is this 480 directly utilized by any load or is it always transformed to 120/240 - 208?

                              Technically should still have separate EGC from grounded conductors per today's codes, but when it was originally installed likely would have been ok to just run grounded conductor to each building and then connect to a grounding electrode at each building and run separate EGC's after first disconnect at each building.
                              I live for today, I'm just a day behind.

                              Comment


                                #45
                                Originally posted by Bretzel View Post
                                =

                                The 480 secondary side of the transformers has only two terminals. There are only three wires leaving the transformer building. T1 connects across leg A and B of the 3 plant distribution wires; T2 connects across leg B and C; T3 connects across legs C and A. There is a stud welded to the bottom of the side of each transformer can. This stud connects to a conductor which bonds each can to the next and then to the same ground peg as the primary. There is no distribution ground or neutral wire from here downstream.
                                [ATTACH=CONFIG]20968[/ATTACH]
                                =
                                thats ungrounded delta

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