Couple of wiring questions

mr.radonmr.radon Solar Expert Posts: 158 ✭✭✭✭✭
I'm installing a array of (45) 230W REC230PE panels using Enphase M190-72-240-S12 inverters.
I have the arrays divided into (3) 15 panel groups (per Enphase). I'm punching through the roof in two locations to bring the AC down to the feeder box with two soladeck enclosures. I'm using 10/3 Romex cable.
In the feeder box I have (6) 15A circuits breakers (installed inside the garage next to the house's panel).
I'm sending the 240V power lines from the feeder box to an externally mounted 2 pole disconnect switch, that goes to my production meter and then into my 200A service box via a 40amp 2 pole circuit breaker.
Grounding: I'm grounding all the racks and panels with UGC-2 CLICKSYS Grounding clips and WEEB 6.7 ground lugs using 6AWG cooper ground wire.

Questions?
1) Is the 10AWG ground wire in the 10/3 Romex spool I'm using serve any purpose since by code I need to run a 6AWG ground wire?
2) Do I run the 6AWG cooper ground wire off the roof through the soladeck enclosures (following the path of the (3) 15A circuits)?
2a) Is there a water tight 6AWG fitting to pass the ground wire into the soladehttp://forum.solar-electric.com/images/editor/menupop.gifck?
3) Does the ground and neutral wires bypass the externally mounted disconnect switch and production meter (goes straight from the feeder box to the 200A service box)?
4) What is the gauge of wire I need to interconnect the feeder box and service box given I have a 40A circuit breaker?

I know a lot of questions. I'm an electrical engineer and have a set of the latest NEC codes (I design DC systems). My panels, inverters and racking system are arriving in a few days and I want to get started with running the electrical wires/conduit before hand.
I can post my hand sketch of the wiring diagram if it helps...

Thanks,

Comments

  • dreesdrees Solar Expert Posts: 481 ✭✭✭
    Re: Couple of wiring questions
    mr.radon wrote: »
    I'm installing a array of (45) 230W REC230PE panels using Enphase M190-72-240-S12 inverters.
    I have the arrays divided into (3) 15 panel groups (per Enphase). I'm punching through the roof in two locations to bring the AC down to the feeder box with two soladeck enclosures. I'm using 10/3 Romex cable.
    In the feeder box I have (6) 15A circuits breakers (installed inside the garage next to the house's panel).
    Why 6 15A breakers in your feeder box when you only have 3 strings?
    mr.radon wrote: »
    I'm sending the 240V power lines from the feeder box to an externally mounted 2 pole disconnect switch, that goes to my production meter and then into my 200A service box via a 40amp 2 pole circuit breaker.
    I think you need a 45A breaker for 45 inverters. Nominal current rating of each inverter is 0.8A * 45 = 36A + 25% NEC safety rating = 45A.
    mr.radon wrote: »
    1) Is the 10AWG ground wire in the 10/3 Romex spool I'm using serve any purpose since by code I need to run a 6AWG ground wire?
    2) Do I run the 6AWG cooper ground wire off the roof through the soladeck enclosures (following the path of the (3) 15A circuits)?
    Depends on the inspector. Running the #6 down to the ground is the "by the book" method. Otherwise you to combine all your #10 grounds to the #6 and run them down from there. Might be worth calling Enphase and see what they suggest. Your local inspector should know, too.
    mr.radon wrote: »
    2a) Is there a water tight 6AWG fitting to pass the ground wire into the soladeck?
    Yes, there are standard wire relief fittings which will seal the #6 wire into the soladeck. Even Home Depot has them.
    mr.radon wrote: »
    3) Does the ground and neutral wires bypass the externally mounted disconnect switch and production meter (goes straight from the feeder box to the 200A service box)?
    Every metal part should be tied into the ground. The neutral will typically just pass through the disconnect box making no connection.
    mr.radon wrote: »
    4) What is the gauge of wire I need to interconnect the feeder box and service box given I have a 40A circuit breaker?
    Depends on the insulation rating of the wire - but #8 to #6. See earlier comment about your 40A breaker.
    See this site for wire ratings (also in the NEC): http://www.cerrowire.com/default.aspx?id=46
    mr.radon wrote: »
    I can post my hand sketch of the wiring diagram if it helps...
    You didn't have to submit the plans to the city to get the permit?
  • mr.radonmr.radon Solar Expert Posts: 158 ✭✭✭✭✭
    Re: Couple of wiring questions
    drees wrote: »
    Why 6 15A breakers in your feeder box when you only have 3 strings?
    I think you need a 45A breaker for 45 inverters. Nominal current rating of each inverter is 0.8A * 45 = 36A + 25% NEC safety rating = 45A.

    The Enphase micro inverters I use have a limit to 15 in a string (per Enphase because of the gauge of wire in their inverters). The Enphase inverters send 240 off the roof. For each phase I need a 15A breaker, phase A & B. So each string of 15 I need two breakers. Or should I be getting a double pole 15A breaker?
    Since I have E, S and W facing arrays I figure unless a supernova hits and the fact I live in the PNW I'll never produce 190W (not even close) from each Enphase at the same time. But the calculations are:
    190WMax/240= .792A X 45 = 35.625A + 25% = 44.5A but you would never hit the 45 A. So, I'm hoping this will fly. Otherwise I guess I have to find a 180A main breaker or upgrade my service connection, or....
    My best case power output is just a fraction of that.
    You didn't have to submit the plans to the city to get the permit?
    No, I did not need a sketch for the permit from L&I.
    For the interconnect agreement with the power company I needed the hand sketch.
    I need to scan it then I'll post it.

    Thanks for all the answers to the questions.

    And boy am I glad the NEC doesn't have any input into the design of vehicle power distribution harnesses.
  • BB.BB. Super Moderators, Administrators Posts: 32,019 admin
    Re: Couple of wiring questions

    As far as I know--Yes, those should be double pole (240 VAC) breakers, not single pole 120 VAC.

    In either case, you will have the same results... I do not believe the Enphase will output any power if one leg breaker is opened. They require both legs for proper operation.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • dreesdrees Solar Expert Posts: 481 ✭✭✭
    Re: Couple of wiring questions
    mr.radon wrote: »
    The Enphase micro inverters I use have a limit to 15 in a string (per Enphase because of the gauge of wire in their inverters). The Enphase inverters send 240 off the roof. For each phase I need a 15A breaker, phase A & B. So each string of 15 I need two breakers. Or should I be getting a double pole 15A breaker?
    Yes, as BB said, you should be using double pole 15A breakers in your PV subpanel.
    mr.radon wrote: »
    Since I have E, S and W facing arrays I figure unless a supernova hits and the fact I live in the PNW I'll never produce 190W (not even close) from each Enphase at the same time. But the calculations are:
    190WMax/240= .792A X 45 = 35.625A + 25% = 44.5A but you would never hit the 45 A. So, I'm hoping this will fly. Otherwise I guess I have to find a 180A main breaker or upgrade my service connection, or....
    My best case power output is just a fraction of that.
    The reason for the 25% safety factor is to avoid nuisance tripping in warmer weather as the breaker warms up under constant load. Since the panels will likely only max out around 180W or less unless it's cool, you'll probably be fine so...

    I don't disagree - but I think to the letter of the NEC the inspector may not like that and you may want to run it by them first. Or as you said, try to find a slightly smaller main breaker and install a 50A backfeed breaker (I think a 45A breaker may be tough to find).
    mr.radon wrote: »
    No, I did not need a sketch for the permit from L&I.
    Lucky! All the local jurisdictions around here need a detailed packet to get the permit approved. Mine was about 12 pages long.
  • Solar GuppySolar Guppy Solar Expert Posts: 1,973 ✭✭✭
    Re: Couple of wiring questions

    You have two issues,

    First, your going to need a much larger breaker than 40 amps for 10350 watts of PV, not exactly how much, off hand I think you can't run more than 80% of the maximum continuous rated amperage of the combined micro-inverters listed output.

    Second, a a much bigger issue is you can't have more than 40 amps for back feed on a 200 amp service ... so you will be required to have less PV/inverters to be NEC compliant.
  • dreesdrees Solar Expert Posts: 481 ✭✭✭
    Re: Couple of wiring questions
    First, your going to need a much larger breaker than 40 amps for 10350 watts of PV, not exactly how much, off hand I think you can't run more than 80% of the maximum continuous rated amperage of the combined micro-inverters listed output.
    Each inverter is rated at 0.8A, so he needs a 45A breaker (0.8 * 45 = 36 * 1.25 = 45).
    Second, a a much bigger issue is you can't have more than 40 amps for back feed on a 200 amp service ... so you will be required to have less PV/inverters to be NEC compliant.
    Or he can downsize the main breaker from 200A to 195A or less (if using a 45A backfeed breaker).
  • mr.radonmr.radon Solar Expert Posts: 158 ✭✭✭✭✭
    Re: Couple of wiring questions

    Looks like the NEC's regarding solar power fall flat here. (or fall in the plain dumb category)
    One array of 15 faces E, one Array of 15 faces South, One array of 15 faces W. So unless there is a SUPERNOVA over my house, there is no way I will get 100% power out of and E,S,W array. Hence never get close to 45A. Even with worst case (best case power wise) I'll never exceed 25A.
    drees wrote: »
    Or he can downsize the main breaker from 200A to 195A or less (if using a 45A backfeed breaker).
  • dwhdwh Solar Expert Posts: 1,341 ✭✭✭
    Re: Couple of wiring questions
    mr.radon wrote: »
    Looks like the NEC's regarding solar power fall flat here. (or fall in the plain dumb category)
    One array of 15 faces E, one Array of 15 faces South, One array of 15 faces W. So unless there is a SUPERNOVA over my house, there is no way I will get 100% power out of and E,S,W array. Hence never get close to 45A. Even with worst case (best case power wise) I'll never exceed 25A.

    Talk to the city engineer. You might be able to get an exception.
  • dreesdrees Solar Expert Posts: 481 ✭✭✭
    Re: Couple of wiring questions
    mr.radon wrote: »
    One array of 15 faces E, one Array of 15 faces South, One array of 15 faces W. So unless there is a SUPERNOVA over my house, there is no way I will get 100% power out of and E,S,W array. Hence never get close to 45A. Even with worst case (best case power wise) I'll never exceed 25A.
    What angle is each roof sloped at? I think you'll be suprised at the some of the power you'll see for 5-10 minutes on partly cloudy days after a cloud passes by.
  • mr.radonmr.radon Solar Expert Posts: 158 ✭✭✭✭✭
    Re: Couple of wiring questions

    27 degrees is the fixed roof pitch.
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Couple of wiring questions

    if the pvs are also sloped at the same angle as your roof is then you will have a production problem in the months not around the summer solstice. your lat is about 47.5 degrees and this should be the minimum angle those pvs should be at (for reference 0 degrees with the pv laying flatly or horizontally) and many add even more to it to optimize the shorter and narrower winter production months.
  • mr.radonmr.radon Solar Expert Posts: 158 ✭✭✭✭✭
    Re: Couple of wiring questions

    Wrong, In Seattle WA 27 degrees produces MORE power then 47.5....;)
    You didn't take into account dome radiation effect in Seattle WA. A panel laid flat (0 degrees) doesn't even loose that much in PV Watts V1 & V2.
    In Seattle the optimal angle is 34 degrees based on NREL solar radiation data collected over the last 20 years.
    Seattle for example: (1KW, 0.77)
    47.5 @ 180degrees = 3.76kWh/m2/day --- 970 kwh
    27.0 @ 180degrees = 3.81kWh/m2/day --- 988 kwh
    0.00 @ 180degrees = 3.34kWh/m2/day --- 854 kwh
    34.0 @ 180degrees = 3.83kWh/m2.day --- 993 kwh
    (yeah crappy numbers because of our rain, rain, rain):roll:
    niel wrote: »
    if the pvs are also sloped at the same angle as your roof is then you will have a production problem in the months not around the summer solstice. your lat is about 47.5 degrees and this should be the minimum angle those pvs should be at (0 degrees with the pv laying flatly or horizontally) and many add even more to it to optimize the shorter and narrower winter production months.

    There are some particular variations from location to location that effects PV systems. I have designed the system to produce on average 9070kwh per year; winter months here in Seattle are very bad for PV systems...
    I've run the hour by hour analysis in PV Watts V1 and V2, for power from the E, S, and W faces. If I take the best solar radiation condition for my arrays, and run the numbers for power produced at -20F (cold=good for PV), I will not get more then 25A combined output. This is where the NEC PV rules fall flat. I don't think they understand a PV panel is a current source, not a voltage source. ie, you can short circuit a PV panel and it can never produce more then a certain amount of current unless something increase the light reaching the panel.

    The only reason I'm doing E, S, W arrays is that is the way my house was built, I could meet my current energy needs with just 15 panels, but I want to have the power to charge a future plug in ecar.
  • dreesdrees Solar Expert Posts: 481 ✭✭✭
    Re: Couple of wiring questions

    So at 27* your south facing panels will be at their optimum a month before/after summer solstice - the sun hits 65.8* on June 20th.

    With the cool weather that Seattle sees, you'll easily see those panels maxing out the inverter at 199W - or 3000W = 12.5A.

    Now, the other panels on the east/west will be at best 27* off at solar noon (assuming you are not tilting those panels south at all which you should really consider doing). Cosine (63) = 0.45 - they'll only be getting about half the sun of the S facing panels at solar noon so yeah, 25A max will probably be close to the maximum you'd ever see for any period of time. Could see you getting up to 30A for very brief periods after clouds pass by and the panels have a chance to cool off, but given that I don't see you running the risk of tripping any 40A breakers.
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Couple of wiring questions

    not wrong as the solar angle in winter will be 47.5 + 23 =70.5 degrees at its solar noon peak for winter solstice. at all other times, and even off to the east and west, the sun is lower in the sky meaning the pvs need tilted even more, but you say i'm wrong and you can do what you want. i would question pv watts showing that much power that far off angle as about 50% of the solar power is lost at around 40 degrees or so off. these figures may be off slightly too from memory, but not that far off.
    btw, solar diffuse radiation will work far better when one deals with solar thermal.
  • mr.radonmr.radon Solar Expert Posts: 158 ✭✭✭✭✭
    Re: Couple of wiring questions

    In Seattle the optimal angle is 34 degrees based on NREL solar radiation data collected over the last 20 years. Here are some of the solar maps:
    http://www.nrel.gov/gis/solar.html PV Watts is based off of. Personally I use PV Watts V2, but there is less then a .1% difference between V1 and V2.

    Did you even bother to look at the PV Watts numbers? Interesting, try PV Watts in another area I'm familiar with, Denver, CO. Optimal placement is NOT due South! Why? Afternoon thunderstorms. You are best placing them at about 165 degrees.

    Due south angled at your geographic latitude is NOT the optimal placement for every fixed solar panel placement.

    Then there is the cost and wind loading factors to consider if you even try to change the angle of the panels, you would NEVER recoup the costs. PV Watts shows that at 47.5 degrees there is a 1.8% NET DECREASE in yearly energy production.

    Everyone should want their FIXED system optimized to produce maximum power over the entire year. Not winter. I'm a Netmetered system, not off grid.

    Lets say I had all the money in the world I could do two axis tracking, I'd get 4.91kWh/m2/day --- 1293 kwh. Not that big of an improvement, only 30.1% over my 27 degree fixed pitch roof. That will never pay off a 2 axis tracking system for 45 panels.

    In Seattle, WA installed angle does not have very much of an effect on what a panel can produce averaged over the course of a year. :roll:
  • BB.BB. Super Moderators, Administrators Posts: 32,019 admin
    Re: Couple of wiring questions

    For my system... Our net metering with Time of Use pays us (at least) ~$0.29 during the summer 6 month peak time and ~$0.12 for the winter cycle (noon to 6pm, Monday thru Friday).

    So--technically, I should maximize my summer production at the expense of winter production because I can get 2.5x the energy banking during the summer afternoons.

    In the end, knowing your billing details and load profile, you may find other optimums settings other than the default.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mr.radonmr.radon Solar Expert Posts: 158 ✭✭✭✭✭
    Re: Couple of wiring questions

    This is the drawing I sent my utility with the Netmetering agreement.
  • mike95490mike95490 Solar Expert Posts: 9,363 ✭✭✭✭✭
    Re: Couple of wiring questions
    mr.radon wrote: »
    This is the drawing I sent my utility with the Netmetering agreement.

    Nice sketch. They may get you for the spliced grounds, some places, you cannot have a joint in the ground wire.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • mr.radonmr.radon Solar Expert Posts: 158 ✭✭✭✭✭
    Re: Couple of wiring questions

    A picture of my 125 Service box. Ready to mount disconnect switch and wire to it. Have all the wiring run in the attic, just waiting on panels to arrive.

    Need to get a ground buss bar for the service panel.

    Question: anyone know if the AC disconnect switch has to have an external handle? Mine you need to flip the cover open to access the switch.
  • BB.BB. Super Moderators, Administrators Posts: 32,019 admin
    Re: Couple of wiring questions

    Depends on your local utility requirements...

    Basically, the utility may require an accessible/lockable disconnect (near meter, not behind locked gates/man-eating dogs) or they will simply pull your meter and kill the power to the whole home.

    So--it is a "service for you" that they can disconnect the Solar GT system and leave power to the rest of your home. So, in that case, they don't "need" a separate disconnect (at least that was how our utility described it--IIRC).

    But, a few years ago, PG&E (Northern California electric and gas company) decided that no external disconnect was needed because the GT inverters were not a danger to the linemen or their equipment.

    So, contact your local utility / building department and see what they require at this time.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mr.radonmr.radon Solar Expert Posts: 158 ✭✭✭✭✭
    Re: Couple of wiring questions

    Basically I need to call PUD. (utility) I know from a previous conversation they want a disconnect switch with an engraved label "pop riveted" on the panel. Yes it says pop rivet in their spec.
    I told them Enphase needs to see power before it sends out power, but they don't want to trust the controller.

    Interesting the wirting in the US to Germany. There you don't even have to ground the panels, and you can bring 1000VDC off the roof without a DC or AC disconnect.
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