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    #16
    Originally posted by kwired View Post
    Main breaker?
    Main lug 3 phase panel. Inverters are single phase but the 6 breakers balance out the phases.

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      #17
      Originally posted by matt123 View Post
      Main lug 3 phase panel. Inverters are single phase but the 6 breakers balance out the phases.
      I think he was asking if it's the main breaker that is getting warm.

      Comment


        #18
        Originally posted by kwired View Post
        From what you mentioned I am seeing 6 breakers with a relatively constant load of 32 amps - which would be 192 amps, all connecting to a 200 amp panel.
        He's got 32A per breaker, but each one is only connected to two of the buses. It's a group of single phase inverters connected phase to phase to a three phase service.

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          #19
          Originally posted by matt123 View Post
          The weird thing is that the bus is not heating up at all. All connections were checked and only hot spot is the breaker casing.
          Sounds like it's coming from the breaker's internals, then, so it must be called "normal" for its use.
          Master Electrician
          Electrical Contractor
          Richmond, VA

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            #20
            Originally posted by matt123 View Post
            Main lug 3 phase panel. Inverters are single phase but the 6 breakers balance out the phases.
            Ok that reduces the current in the 200 amp panel - my comment of 192 amps was for a single phase source.

            Don't know enough about PV systems, can you tie such units to a three phase system or do you need an inverter(s) with three phase output?
            I live for today, I'm just a day behind.

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              #21
              Originally posted by kwired View Post
              ...

              Don't know enough about PV systems, can you tie such units to a three phase system or do you need an inverter(s) with three phase output?
              I believe it's become less common to use single phase inverters as three-phase have become more available, but yes, you can do it.

              Comment


                #22
                Originally posted by kwired View Post
                Ok that reduces the current in the 200 amp panel - my comment of 192 amps was for a single phase source.

                Don't know enough about PV systems, can you tie such units to a three phase system or do you need an inverter(s) with three phase output?
                Yes, you can. You would connect the single phase inverters (ideally a number of them divisible by three for balancing) phase to phase (A-B, B-C, and C-A) or phase to neutral (A-N, B-N, and C-N). As jben says, it's not as common as it used to be when there were a lot fewer 3 phase inverters. My first commercial system was 72 SMA 7000's phase to neutral on a 480V service.

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                  #23
                  Originally posted by matt123 View Post
                  Went out today and checked it out and the breakers are reading 135 degrees. Seems hot so I called square d and talked to one of their engineers and he said that breaker can go up to 185. Anyone have any inverters running 32 amps at that temp? Seems hot or am I just over thinking it?
                  My help just replaced a panel interior where the breakers were getting to the 180 degree range. Bad connection to the buss. They used a small handheld thermal scanner to read the temps.
                  Tom
                  TBLO

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                    #24
                    Originally posted by ggunn View Post
                    Yes, you can. You would connect the single phase inverters (ideally a number of them divisible by three for balancing) phase to phase (A-B, B-C, and C-A) or phase to neutral (A-N, B-N, and C-N). As jben says, it's not as common as it used to be when there were a lot fewer 3 phase inverters. My first commercial system was 72 SMA 7000's phase to neutral on a 480V service.
                    Do they have ability to know if they are supplying 208 vs 240 volts? Either automatic or with manual settings? Same unit that supplies 240 volts line to line being used on 208 three phase would need to adjust I would think.

                    Something that is single voltage and connects line to neutral would put out 120 volts either way.
                    I live for today, I'm just a day behind.

                    Comment


                      #25
                      Originally posted by kwired View Post
                      Do they have ability to know if they are supplying 208 vs 240 volts? Either automatic or with manual settings? Same unit that supplies 240 volts line to line being used on 208 three phase would need to adjust I would think.

                      Something that is single voltage and connects line to neutral would put out 120 volts either way.
                      In my case it was 277V (phase to neutral on 480V). I do not remember if we had to tell the inverters to run at 277V or if they just did it in response to the voltage they saw; it was nearly 10 years ago.

                      Comment


                        #26
                        Originally posted by kwired View Post
                        Do they have ability to know if they are supplying 208 vs 240 volts? Either automatic or with manual settings? Same unit that supplies 240 volts line to line being used on 208 three phase would need to adjust I would think.

                        Something that is single voltage and connects line to neutral would put out 120 volts either way.
                        Judging from the products out there, it's not that hard to engineer a product that can handle both 240 and 208, and even 277. It just needs components rated high enough for the highest voltage and highest current it would be used at. The rest is just software. The datasheet will usually specify a different max current output for the different voltages. If there is a neutral then detection is usually automatic, if there is not then manual, there are exceptions to that.

                        Comment


                          #27
                          Originally posted by jaggedben View Post
                          Judging from the products out there, it's not that hard to engineer a product that can handle both 240 and 208, and even 277. It just needs components rated high enough for the highest voltage and highest current it would be used at. The rest is just software. The datasheet will usually specify a different max current output for the different voltages. If there is a neutral then detection is usually automatic, if there is not then manual, there are exceptions to that.
                          I checked up the other day. Not so hot but some vibration through the breakers. , slight humming. Thoughts?

                          Comment


                            #28
                            Originally posted by matt123 View Post
                            I checked up the other day. Not so hot but some vibration through the breakers. , slight humming. Thoughts?
                            Normal.
                            Tom
                            TBLO

                            Comment


                              #29
                              Single-phase Inverters Connected to Three-phase Grid

                              Originally posted by ggunn View Post
                              Yes, you can. You would connect the single phase inverters (ideally a number of them divisible by three for balancing) phase to phase (A-B, B-C, and C-A) or phase to neutral (A-N, B-N, and C-N). As jben says, it's not as common as it used to be when there were a lot fewer 3 phase inverters. My first commercial system was 72 SMA 7000's phase to neutral on a 480V service.
                              This isn't entirely correct. If single-phase inverters are connected to a three-phase grid topology, the system must comply with Articles 705.42 and 705.100. Conditions exist (e.g. 240 volt delta) where one phase could open, creating an "open delta". Single-phase inverters connected in such a configuration won't sense the lose of one phase, and will continue to export power.

                              To remedy this condition requires the use of external sensing and control hardware to open all three phases should one phase open. For those not familiar with an open delta, the voltage across the "open" phase will still measure essentially the same as for the other two phases. Inverters connected to the "open" phase will not sense the loss of that phase, and will continue to export power. Depending on the wattage of the solar array connected across an open phase, it's entirely possible to overload the transformer, since an open delta is rated for 57.7% of a full delta transformer.

                              There is also a risk of phase imbalance if part of an array should cease to export power. This could occur if a breaker in that array should trip, and the other two arrays continue in full operation.

                              Single-phase inverters *can* be used in a three-phase topology if all requirements in Article 705 are met. This requires multiple points of sensing, multiple types of sensing, and three-pole relays or contactors of appropriate ratings to open all three phases with the loss of any one phase in the system. Grid-interactive inverters will cease exporting power with loss of the grid as required in UL 1741, UL 1741SA, and UL 62109. IEEE 1547 contains the details of the required shutdown conditions, and is a subset of the UL Standards just mentioned.

                              Since inverters are a source, not a load, traditional methods of sensing an open phase may not be effective in such cases. Moreover, solar inverters are a current-limited current-source, making over-current in the event of the loss of a phase an impossibility, as would be the case such as for a large three-phase motor.

                              Lacking the protections just referenced, a Code violation exists when single-phase inverters are connected to a three-phase grid because inverters on the unaffected phases won't cease to export power in the event of the loss of a phase.

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