Inverter Error: AC Voltage Too High - wire not thick enough?

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HX_Guy
HX_Guy Solar Expert Posts: 296 ✭✭✭✭✭✭
in Solar Beginners Corner #1
After finishing up the install today, my installer hooked up a test meter and we tried to test the system. I'm using a SolarEdge inverter and after it synced with the optimizers, we got a "AC Voltage Too High" error (and apparently it also burnt out his test meter, or maybe it was a coincidence, but it would no longer turn on).

Looking online, seems someone else had this problem and it may either be that a firmware update is needed or that the wire gauge is too small.
I'm trying to figure out what the proper wire gauge should be but getting different answers, can anyone help? One online calculator says 4AWG while another says 8AWG. The installer put in 6AWG and said it should more more than plenty thick.

Circuit voltage is 240v and the wire run from the service panel, though the disconnect, through the meter, to the inverter is 21 ft in total length.
The inverter output current is 48A (the backfeed breaker is 60A). What size wire should be used here?
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  • HX_Guy
    HX_Guy Solar Expert Posts: 296 ✭✭✭✭✭✭
    #2
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    Re: Inverter Error: AC Voltage Too High - wire not thick enough?

    Quick follow up question...when using these online conductor size calculators, do I use 48A or 60A for the current? They give very different answers.
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #3
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    Re: Inverter Error: AC Voltage Too High - wire not thick enough?

    #6 wire is only good for 37 amps continuous.
    Your wire HAS to be rated to handle 60A, if it's attached to a 60A breaker, otherwise it will burn up before the breaker would trip. That gives your 48A a little bit of a cushion.

    http://www.powerstream.com/Wire_Size.htm
    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
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  • HX_Guy
    HX_Guy Solar Expert Posts: 296 ✭✭✭✭✭✭
    #4
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    Re: Inverter Error: AC Voltage Too High - wire not thick enough?

    So then the 6AWG is no good and we need 4AWG right? Which also means we need 1" EMT not the 3/4" he used. He has to redo the whole outdoor conduit installation, unbelievable.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #5
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    Re: Inverter Error: AC Voltage Too High - wire not thick enough?

    yTwo sets of calculations... If you have a 48 AAC maximum current, then the circuit (and breaker/wiring/etc.) needs to be rated 1.25x larger (rounded up) for actual rating. Or:
    • 48 AAC maximum current (array and/or inverter maximum rated output) * 1.25 NEC derating = 60 Amp minimum branch circuit
    So, the wiring needs to be rated for 60 amps minimum (i.e., copper vs aluminum, ambient temperature of installation, type of insulation, wet/dry environment, conduit size and fill factor) all will give you THWN 6 awg (or whatever). Use the NEC manual (or online wire sizing program) to pick the right values (i.e, ambient temperature, fill factor, etc.). The beginning chart looks something like:

    https://lugsdirect.com/WireCurrentAmpacitiesNEC-Table-301-16.htm

    Next, you need to look at the length of wire run and acceptable voltage drop (or voltage rise in a GT Inverter's AC output). Typically, we size the wire run for 3% to 1% voltage drop (moving from 3% to 1.5% voltage drop is ~3 AWG larger wire diameter--So there is 2x as much copper and 2x the costs). Use the 48 AAC for this calculation (voltage drop).
    • 240 VAC * 3% = 7.2 volt drop (or "rise" at the GT inverter)
    • 240 VAC * 1% = 2.4 volt drop
    Also, you need to look at operational voltages. More or less, the acceptable AC voltage range is around +10% to -15% or:
    • 240 VAC * 1.10 = 264 VAC maximum
    • 240 VAC * 0.85 = 204 VAC minimum
    Note, there are mfg. tolerances, and you may end up with 260 VAC being the maximum the GT inverter is guarantee to operate without faulting. Minimum operating voltage may be 90%--Or 214 VAC.

    Note that these numbers may be programmable in the GT inverter by the installer (password protected configuration).

    So, looking at the allowed voltage drop (rise) 3% gave us ~7.2 volts maximum. Which means the maximum line voltage from the house panel (or even the street transformer) would be:
    • 260 volts - 7.2 volts = 252.8 volts AC line maximum (with 7.2 volt rise to the GT inverter)
    My home's line voltage seems to run around 244 to 250 VAC (at the meter, I have a digital utility meter that gives me the Line to Line voltage).

    If your area has "high" line voltage or varies between winter and summer (summer, lots of water pumping and Air Conditioning, the utility may "crank up" the line voltage to allow for daytime sag... Etc...

    When the line voltage is "High", you may need heavier copper wire from the GT inverter to the Main Panel to avoid "over voltage" error at the GT inverter (as an example).

    Anyway, that is the basics.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • SkiDoo55
    SkiDoo55 Solar Expert Posts: 414 ✭✭✭
    #6
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    Re: Inverter Error: AC Voltage Too High - wire not thick enough?

    Electrican2 calculator for 48 amp, 240 VAC using THNN2 90 C wire comes up with #4 wire with 60 amp or 70 amp max breaker. Shows about 0.3 % voltage drop for 21 ft run. Yes fill tables show 1" EMT min for 3 #4 wires with either #8 or #10 ground wire in it.
    might need to recalculate your array max voltages and look at what the inverter normal operating ranges are. Could be high on input, out of MPPT tracking range.
    GT3.8 w/4600W Trina 230W, TX5000 w/5000W ET-250W, XW4024 w/1500W ET-250W, 4 L16, 5500W Gen. (never had to use) Yet!!
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  • HX_Guy
    HX_Guy Solar Expert Posts: 296 ✭✭✭✭✭✭
    #7
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    Re: Inverter Error: AC Voltage Too High - wire not thick enough?
    SkiDoo55 wrote: »
    Electrican2 calculator for 48 amp, 240 VAC using THNN2 90 C wire comes up with #4 wire with 60 amp or 70 amp max breaker. Shows about 0.3 % voltage drop for 21 ft run. Yes fill tables show 1" EMT min for 3 #4 wires with either #8 or #10 ground wire in it.
    might need to recalculate your array max voltages and look at what the inverter normal operating ranges are. Could be high on input, out of MPPT tracking range.

    Thanks for all the replies.

    The error is definitely on the AC output side. Per the manual, it says:

    AC Voltage Too High
    - AC voltage surge. The internal hardware that measures AC voltage has measured substantially high sudden output voltage.
    If the fault persists:
     Check the AC connection to inverter.
     Verify that the inverter is set to the correct country.
     Check with the grid operator if a large surge source or irregular load exists near the site.
     Verify that the output wire size matches the distance between the inverter and the location of the grid connection.
     Use a larger gauge wire for the AC output.

    Even if say we test it again tomorrow and it work ok *for now*, it sounds like the wire needs to be changed out to 4AWG and 1" EMT anyway, right?
    This is confusing, I don't get why there are so many different answers. For example looking at Southwire's spec sheet for their SIMpull THWN-2 wire (the stuff the installer used), it says the allowable ampacities for 6AWG wire is 55A @ 60ºC, 65A @ 75ºC, and 75A @ 90ºC.

    http://www.southwire.com/ProductCatalog/XTEInterfaceServlet?contentKey=prodcatsheet276
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  • ggunn
    ggunn Solar Expert Posts: 1,973 ✭✭✭
    #8
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    Re: Inverter Error: AC Voltage Too High - wire not thick enough?
    mike95490 wrote: »
    #6 wire is only good for 37 amps continuous.
    Your wire HAS to be rated to handle 60A, if it's attached to a 60A breaker, otherwise it will burn up before the breaker would trip.

    Conductors connected to a 60A breaker need only have a derated ampacity of more than 50A. When you are working the problem the other way and come up with the conductors' ampacity, you may protect them with a breaker the next size up unless you are dealing with current of more than 800A.
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