Problem with electrical inspector

So according to the inspector I cannot connect my inverter output to my sub-panel it must go directly to my main service which is another 700 feet so can I run full 600 VDC all the way using #8 teck cable not saving me money. The output of the solar will vary all the time so the max is 600V but how do you size wire when the output varies? 1 series has 8 panels each panel (4.98A) Vmp47.2 there are 3 series 24 panels. I have no clue:cry:

Comments

  • ggunnggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: Problem with electrical inspector
    Farmer wrote: »
    So according to the inspector I cannot connect my inverter output to my sub-panel it must go directly to my main service which is another 700 feet so can I run full 600 VDC all the way using #8 teck cable not saving me money. The output of the solar will vary all the time so the max is 600V but how do you size wire when the output varies? 1 series has 8 panels each panel (4.98A) Vmp47.2 there are 3 series 24 panels. I have no clue:cry:
    A couple of things...

    Your inspector probably found you to be in violation of the 120% rule in your subpanel. There are ways of dealing with that.

    The voltage of your PV system, whether on the AC or DC side of the inverter, will not vary by much. The current (DC and AC) will vary quite a bit with differences in the strength of the sunlight striking your modules.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Problem with electrical inspector

    The output of the inverter will be 240 VAC. 600 Volts is the maximum rating for the wire and is not particularly relevant to the case. This should not be confused with the DC input to the inverter, and it sounds like it is.

    What is relevant is the current and Voltage drop over the length of the wire. 700 feet is a lot of length and a lot of V-drop whether you're talking about the AC out or the DC in.

    Need some more details about what's going on here.
  • solar_davesolar_dave Solar Expert Posts: 2,366 ✭✭✭✭
    Re: Problem with electrical inspector

    Some AHJ require a external disconnect for the PV at the main panel, I suppose you could add that to your sub-panel feed to get around the requirement. Hopefully your line to the sub-panel is heavy enough as well.

    The inverter to AC can be anywhere I think, mine is located behind a locked gate about 30 ft from the mains. What is the AC amps out from your inverter? Perhaps the AC line is a cheaper feed.
  • FarmerFarmer Registered Users Posts: 24
    Re: Problem with electrical inspector

    I will explain it better he will not accept any connection made to the sub-panel which is being feed by 250mcm alu. He will not allow back-feed both ways on the 250mcm. He would like a new installed run to go back to the meter where they would like a fused disconnect and then to my main service. I can leave the inverter out there 700 feet away and run 240VAC to the disconnect but the wire may be better to run 700 feet 600VDC to the inverter and I can place it beside the disconnect. Does this Help?:D
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Problem with electrical inspector

    I think we're getting closer. :D

    You can either run the 240 VAC all the way back to the main panel, or move the inverter closer and run the DC the long distance to the inverter. Right? If so we'd need to know the operating range of the DC. According to your first post the Vmp per panel is 47.2 and there are three parallel strings of eight in series. Right? If so the the PV array is running 378 Volts and (4.98 * 3) 15 Amps. This should be much easier to accommodate across 700 Feet. Looks like 8 AWG copper would just about handle this with minimal Voltage drop. And there would not be an issue with the Voltage drop on the AC side which could cause the inverter to cut in/out.
  • FarmerFarmer Registered Users Posts: 24
    Re: Problem with electrical inspector
    I think we're getting closer. :D

    You can either run the 240 VAC all the way back to the main panel, or move the inverter closer and run the DC the long distance to the inverter. Right? If so we'd need to know the operating range of the DC. According to your first post the Vmp per panel is 47.2 and there are three parallel strings of eight in series. Right? If so the the PV array is running 378 Volts and (4.98 * 3) 15 Amps. This should be much easier to accommodate across 700 Feet. Looks like 8 AWG copper would just about handle this with minimal Voltage drop. And there would not be an issue with the Voltage drop on the AC side which could cause the inverter to cut in/out.

    Yes DC seems a better way So do you think I can add another panel to each string to bring up the voltage and make up the loss?. Max ISC 5.31A plus cold factor changes the voltage to 67.8V. 9X67.8=610.2V minus the distance 18.3V (3%) =under 600V is that right?
  • BB.BB. Super Moderators, Administrators Posts: 30,642 admin
    Re: Problem with electrical inspector

    Your GT Inverter mfg. should have a software program (or website) that would allow you to plug in the numbers... In some cases, it may be worth while to call the customer support line and get them to send you a letter "blessing" your setup (or have your installer do it--if you end up with one).

    The "nice" thing about making your long run the DC version--is the voltage can be "anything" and the GT Inverter will adjust. With the long run being AC, your AC wiring must be between ~212 and 264 VAC--Outside of those limits (+/- for some measurement errors--like 260 VAC peak possibly), the GT inverters will shut down (high/low line from utility, or high voltage "rise" from GT inverter to Utility connection--more common for folks "in the middle of no-where" where the AC Line voltage is less than ideally regulated).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • solarixsolarix Solar Expert Posts: 713 ✭✭
    Re: Problem with electrical inspector

    What do your plans say?
    Did your AHJ already approve the way you want to do it and now the inspector is trying to change the deal? If so, you may be able to get him to stick to the already approved plans. The codes do allow for backfeeding subpanels, but on the other hand, most utilities and AHJ's don't go for it as they want all the evil, dangerous solar stuff located at the service entry where they can have easy access to shutting you off.
  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Problem with electrical inspector
    Farmer wrote: »
    I will explain it better he will not accept any connection made to the sub-panel which is being feed by 250mcm alu. He will not allow back-feed both ways on the 250mcm. He would like a new installed run to go back to the meter where they would like a fused disconnect and then to my main service. I can leave the inverter out there 700 feet away and run 240VAC to the disconnect but the wire may be better to run 700 feet 600VDC to the inverter and I can place it beside the disconnect. Does this Help?:D

    Has the inspector cited a particular code section or sections to justify his position? If he has, then it will give you a better idea what your options are for complying (or whether he is misinterpreting the NEC or local requirements.) There is nothing specific about using 250mcm Al by itself that is a problem, but there may be issues when you add local loads at the inverter end into the picture.
    Is he telling you to bring the inverter output through a fused disconnect to the supply (meter) side of the main panel (called a "supply side tap") or to bring it into the main panel through its own backfed breaker?
    You have not told us what amperage you will be producing from your inverter, what its rated max output is, or what the maximum power output from your panels might be.
    Another important factor is what loads are being powered by the sub-panel and what size breaker at the main panel is feeding the sub panel.

    If you are not interested in going this route, then you can look at one of the voltage drop calculators listed in other threads to see what size wire you would have to use to bring the DC all the way from the panels to an inverter location closer to the main panel. Running 600 volts DC will definitely use smaller wires for the same power loss than running 240 volts AC. But the 600 volt system operation could add additional code requirements on the wiring methods.
    Finally, running the inverter output 700 feet with too large a voltage drop can prevent some types of GTIs from sensing a good connection to the grid and prevent them from even starting. Or the higher voltage at the subpanel when the GTI is operating may cause problems for loads connected at the subpanel.

    Without a lot more detail it is hard to give you more specific advice.
    SMA SB 3000, old BP panels.
  • FarmerFarmer Registered Users Posts: 24
    Re: Problem with electrical inspector
    inetdog wrote: »
    Has the inspector cited a particular code section or sections to justify his position? If he has, then it will give you a better idea what your options are for complying (or whether he is misinterpreting the NEC or local requirements.) There is nothing specific about using 250mcm Al by itself that is a problem, but there may be issues when you add local loads at the inverter end into the picture.
    Is he telling you to bring the inverter output through a fused disconnect to the supply (meter) side of the main panel (called a "supply side tap") or to bring it into the main panel through its own backfed breaker?
    You have not told us what amperage you will be producing from your inverter, what its rated max output is, or what the maximum power output from your panels might be.
    Another important factor is what loads are being powered by the sub-panel and what size breaker at the main panel is feeding the sub panel.

    If you are not interested in going this route, then you can look at one of the voltage drop calculators listed in other threads to see what size wire you would have to use to bring the DC all the way from the panels to an inverter location closer to the main panel. Running 600 volts DC will definitely use smaller wires for the same power loss than running 240 volts AC. But the 600 volt system operation could add additional code requirements on the wiring methods.
    Finally, running the inverter output 700 feet with too large a voltage drop can prevent some types of GTIs from sensing a good connection to the grid and prevent them from even starting. Or the higher voltage at the subpanel when the GTI is operating may cause problems for loads connected at the subpanel.

    Without a lot more detail it is hard to give you more specific advice.

    Yes he did refer to a new section his friend wrote Section 64 and the layout drawings to stick to. Yes I can see the load pushing back on the same line having issues. looking at the drawings in the code book it shows the line from the panel supply to dc disconnect and then the inverter and Ac disconnect which could be your utility disconnect as well, then into your main service box. I was told to stick to the drawing examples. The inverter is sunny boy 8000 I have 27 CS5P 235W panels but only used 24 because the voltage put me over 600V when the cold factor is added in. I am hoping for 15DC amps at just under 600V when it reaches the inverter. The main feed the sub with a 60A breaker during winter 1-2 amps, summer 30-40 amps are the loads. So I priced out #8 teck 221meters $1650 but I think running 3 #4 aluminum wires in DB2 may be cheaper way to go and I will ground it at the source. So Inetdog I hope I answered your questions And Solarix my electrician liked the plan I drew. It just added a disconnect between the sub and the main service using 250mcm and 200A disconnect with 60A fuses hard to get 250mcm in a 60A box. Thanks for your replies And how do I add pictures I tried and it does not work the file may be too big any clues???
  • bmetbmet Solar Expert Posts: 630 ✭✭
    Re: Problem with electrical inspector

    This dialog of aluminum wiring has me spooked. I used some #10 aluminum wire in a 12 VDC circuit for a Solsom CFL. I wired it wrong, and the aluminum wire melted at the outlet box. It was an eye opener for proper fusing.
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