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  • Ground and Neutral Wires

    I am installing 26 Itek 280 watt roof mounted panels with a Solectria PVI-7600-TL Inverter. I have installed a AC disconnect and a production meter base as required for my state incentives.

    I have ran the ground from the panels on the roof to the inverter however I am not sure if it is best to run the ground through the Ac disconnect and production meter box into the breaker panel and connect to ground there?

    I am also not sure how to wire the Neutral - do I just go from the inverter to the breaker panel or do I need to make any connections with the Neutral at the AC disconnect or production meter?

    Thanks for any help.

    AC Disconnect & Meter.jpg
    Inverter.jpg
    Solar Panels.jpg

  • #2
    Don't know anything about production meters, so can't help you there.

    As for the grounding.
    My belief is that the EGC would need to be connected to any and all metal boxes that it passes through.
    There is a lug just for that purpose on many/most boxes.

    Is this an EGC or a GEC?
    (And if you don't know, you better figure it out)
    My *guess* would be it's only EGC - but if it is GEC then you have other rules you need to deal with which I'm not familiar with.

    Good luck.

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    • #3
      The utility style round meters for 120/240 single phase service do not have a point to which the neutral is connected. There will usually be a neutral terminal in the meter base assembly which can be used to bond the neutral to the ground. But it does not connect to the meter.

      The current consensus, although not a strong one, is that the PV disconnect for a line side connection should bond the neutral to the ground, just as the existing service equipment does. You can make that bond in the meter base or at the PV disconnect, assuming they are adjacent. But if the PV connection is load side instead, you must NOT bond the neutral to the ground at the PV disconnect or at the meter base.

      Just for your information, the revenue grade meter measures the current in both L1 and L2 and assumes that any imbalanced current is traveling over the neutral. This is a perfectly good assumption.
      But it also assumes that the L1-N voltage and the L2-N voltage are both exactly half of the L1-L2 voltage, which is the only one it actually measures.
      That is a fair approximation as long as the imbalance is not too large and the resistance in the neutral does not cause a voltage drop of more than a volt or two.
      SunnyBoy 3000 US, 18 BP Solar 175B panels.

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      • #4
        What neutral? Your inverters are 240 volts right? You have no need to carry a Neutral as you have no 120 volt supply/load connections.
        MSEE, PE

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        • #5
          Originally posted by Sunking View Post
          What neutral? Your inverters are 240 volts right? You have no need to carry a Neutral as you have no 120 volt supply/load connections.
          Current UL listing requirements for some categories of GTI, probably for anti-islanding reasons but who knows for sure, require that a neutral reference be provided (no current drain) and that the 240V GTI shut down if the imbalance between the measured L1-N and L2-N voltages gets above a certain limit (somewhere less than 10V if I recall correctly.)
          SunnyBoy 3000 US, 18 BP Solar 175B panels.

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          • #6
            Originally posted by inetdog View Post
            Current UL listing requirements for some categories of GTI, probably for anti-islanding reasons but who knows for sure, require that a neutral reference be provided (no current drain) and that the 240V GTI shut down if the imbalance between the measured L1-N and L2-N voltages gets above a certain limit (somewhere less than 10V if I recall correctly.)
            Interesting I stand corrected. At the moment cannot see any reason for Neutral, as Ground from the N-G bond point in the service disconnect would do the same thing. Sounds like an extra conductor with no purpose to me. I gotta be missing something.
            MSEE, PE

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            • #7
              So it sounds like I can run the neutral all the way to the breaker panel?

              For the ground my inverter has a grounding electrode terminal bar and a grounding electrode terminal connection for AC out. I am not sure where to make the grounding connections.

              Comment


              • #8
                Originally posted by Sunking View Post
                Interesting I stand corrected. At the moment cannot see any reason for Neutral, as Ground from the N-G bond point in the service disconnect would do the same thing. Sounds like an extra conductor with no purpose to me. I gotta be missing something.
                Arguably the EGC in any outlet, switch, etc could just be used instead of neutral.
                But they aren't (or at least aren't supposed to be - I just rewired a lighting circuit where the ground wire was used as the current return because the neutral inside of the romex came from the factory missing 1/2" of the wire. And rather than pull new romex, the electrician 40 years ago just used the wires he had)

                Anyhow - back to the neutral in a GTI inverter.
                My inverter requires EGC for grounding (just like almost any equipment)
                And a neutral that it uses for detecting if there's any issues with the L1-N or L2-N voltages.
                If either of those get out of range (either too high or too low I think) it disconnects from the grid.
                I wouldn't be suprised if it also uses some small amount of power on one of them for the electronics. (to power the small cpu it has, the LCD screen, the ethernet, etc.)
                The neutral and the EGC are tied together in the main panel only 2 feet away (~3ft by wire) But I'm sure if only a single wire were used for both bonding and the neutral reference it'd be considered a code violation.
                Logically it would work and there's really no difference. BUT it's simple enough to pull the two wires and just have it be code compliant.

                Comment


                • #9
                  Originally posted by Sunking View Post
                  Interesting I stand corrected. At the moment cannot see any reason for Neutral, as Ground from the N-G bond point in the service disconnect would do the same thing. Sounds like an extra conductor with no purpose to me. I gotta be missing something.
                  It seems to me that there are at least two possible reasons for requiring the neutral.
                  1. To maintain the effective separation of function of neutral and EGC by not even using the EGC as a minimal current voltage reference. This is in line with not allowing a three wire dimmer to use EGC instead of neutral for its neutral reference. Also because even a small, as power goes, current in the EGC could cause an upstream GFCI to trip.
                  2. To make sure that the voltage balance determination is made correctly if there is a high resistance neutral and unbalanced loads upstream of the inverter output. L1-G/L2-G balance does not assure L1-N/L2-N balance.

                  PS: Some inspectors are currently insisting that the reference-only neutral be counted as a CCC, or even that that neutral cannot be sized smaller than the line conductors which are actually carrying the inverter output current.
                  I do not think that [2014] has made this particular point any clearer.
                  Last edited by inetdog; 05-26-2015, 04:45 AM.
                  SunnyBoy 3000 US, 18 BP Solar 175B panels.

                  Comment


                  • #10
                    Originally posted by inetdog View Post
                    Also because even a small, as power goes, current in the EGC could cause an upstream GFCI to trip.
                    Not sure how that would be possible as there should be no upstream GFCI breakers. Only thing up stream should the Main Service Breaker. Even if it were a sub panel you would not feed it with a GFCI feeder as it would be operating constantly from false trips. Anyway I was just curious because there are no 120 volt loads I know of.
                    MSEE, PE

                    Comment


                    • #11
                      Not familiar with Solectra inverters per se, but assuming it is a transformer type with grounded DC conductors, the inverter ground should have both an EGC (safety ground) as well as a GEC (lightning protection). The EGC is used to ground all metallic enclosures and conduit etc. to protect against ground faults (shorts to ground) and needs to not carry current (except during a fault). Thus you still need a neutral as the inverter does have some minor circuitry using it (if nothing else than to monitor the phase voltages). The neutral should wire from the inverter through any disconnects and meters (without connecting to them) to the breaker panel. Can be a reduced size from the hot wires though. The GEC is handled 2 ways in the code. Either can be outside the conduit or inside the conduit. Outside is preferable as the potentially high currents of a lightning hit are less induced into the active wiring, but being exposed, needs to be 6ga to meet the durability requirement. Inside is sometimes preferable on long runs and can double as the EGC, but because of the "choking effect" of a conductor in a metal conduit, code requires the conduit to be bonded on both ends. With a disconnect and meter in the AC path, this can be a real hassle. Don't ask me why, but the field engineers for the transformerless inverters say that because the DC side is not grounded, the need for a GEC eliminated altogether.
                      BSEE, R11, NABCEP, Chevy BoltEV, >3000kW installed

                      Comment


                      • #12
                        Originally posted by solarix View Post
                        Don't ask me why, but the field engineers for the transformerless inverters say that because the DC side is not grounded, the need for a GEC eliminated altogether.
                        The details of this depend strongly on which version of the NEC is in effect. The statement is pretty close to true for areas subject to the 2014 NEC. Note however that a GEC is still needed somewhere for grounding/bonding the frame and other exposed metal of the panel array.
                        SunnyBoy 3000 US, 18 BP Solar 175B panels.

                        Comment


                        • #13
                          Originally posted by Sunking View Post
                          What neutral? Your inverters are 240 volts right? You have no need to carry a Neutral as you have no 120 volt supply/load connections.
                          Seems strange but the installation manual for that inverter clearly shows both a neutral and ground wire coming from the house panel being terminated on distinct terminal blocks (PE for ground & N for neutral) along with L1 & L2.

                          There is also a wiring diagram (Figure 16) on page 26 for a 240v/120v split phase AC grid connection showing the Neutral wire from the inverter connected to the center or ground terminal of the 240/120v transformer.

                          My guess would be for the OP to just run the neutral wire through the AC disconnect switch to the neutral bus in the main panel.
                          Last edited by SunEagle; 05-26-2015, 01:55 PM. Reason: added last sentence

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                          • #14
                            Originally posted by SunEagle View Post
                            Seems strange but the installation manual for that inverter clearly shows both a neutral and ground wire coming from the house panel being terminated on distinct terminal blocks (PE for ground & N for neutral) along with L1 & L2.
                            Huh? PE = Protective Earth which is not a term used in the USA or NEC. Only place you see that term is UK, and they don't use 120 volts so now I am even more confused. Oh well I really do not care and will step out of this.
                            MSEE, PE

                            Comment


                            • #15
                              Originally posted by Sunking View Post
                              Huh? PE = Protective Earth which is not a term used in the USA or NEC. Only place you see that term is UK, and they don't use 120 volts so now I am even more confused. Oh well I really do not care and will step out of this.
                              The manual is specific to US installations and mentions the required NEC section 690 requirements. It also refers to DC AFCI compliance UL 1699B standard. Not sure if the PE or "equipment grounding conductor" is a carry over from European equipment or not.

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