voltage at ground wire

solarhills99solarhills99 Registered Users Posts: 15 ✭✭
Recently getting my off grid system grounded on a distant out building using a separate from the house ground rod. If I put a volt meter on my ground rod wire and my positive combiner box terminal it reads the voltage of the panels.  Is this correct.
Thanks.

Comments

  • mike95490mike95490 Solar Expert Posts: 8,240 ✭✭✭✭✭
    Is the minus of the panels tied to Ground ?

    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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  • solarhills99solarhills99 Registered Users Posts: 15 ✭✭
    no, the minus is not.
  • mcgivormcgivor Solar Expert Posts: 2,815 ✭✭✭✭✭
    The controller itself may be negative ground, is there a ground lug provided? 
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery bank 
    Second system 1890W  3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah FLA 24V nominal used for water pumping and day time air conditioning.  
    5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
  • BB.BB. Super Moderators, Administrators Posts: 29,002 admin
    I am not quite sure which ground rod location vs combiner box location (i.e, house ground rod and combiner box at array?).

    It does sound like the combiner box has a "connection" between array + and the box--And the box itself does not have a "hard ground" between its metal and the ground rod.

    The connection from array + to box may be just some dirt/corrosion/moisture, and if you use a resistor or lamp between box and ground, you may "short out" the voltage to zero volts--And have very little (1/1,000 of an amp or less) current flow. Digital volt meters have something like 1,000,000 to 10,000,000 Ohm of input resistance--And it is easy to pick up "stay voltages".

    It is common for a tech to have a 120 volt 20-100 Watt filament lamp with alligator clips to provide loading when trying to track down issues like this.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • TecnodaveTecnodave Registered Users Posts: 356 ✭✭✭
    edited May 15 #6
    BB  and anybody interested in this issue.

    Fluke has addressed the high impedance DVM problem with a new line of "electricians"   DVM's that have 10k ohm's /volt input impedance.  These will load down a circuit enough that stray voltages are drained off. May I recommend the Fluke 117 electricians DVM . It is specially designed for the commercial electrician.  I bought one and it is very handy for this situation.  It will not be useful in very low power electronics , digital circuits, etc. use due to the fact that it will load down a circuit and give false readings due to its loading. Fluke standard is 14 megohm input impedance as seen on the 77,87,177,377 etc.

    I use a 7 watt incandescent lamp with alligators  as a loading device. You don't need anything larger than that.

    david
    2 Classic 150, 2 Kid, 5 arrays 7.5 kw total  2ea.  2S6P Sharp NE-170/NE-165, 1ea. 12P Sanyo HIT 200,  2ea. 4/6P Sanyo HIT 200, MagnaSine MS4024AE, Cotek SK-1500,Exeltech 1100,  2 Banks L-16 battery, Rolls-Surette S-530 and Interstate Traction, Shunts with whizbangJr and Bogart Tri-Metric, iCharger i208B  dc-dc buck/boost converter with BMS for small form lithium 8S 16650 or 10S LiFePO4,
  • BB.BB. Super Moderators, Administrators Posts: 29,002 admin
    edited May 16 #7
    This meter also has a "low impedance" mode of ~3,000 Ohms (as I recall):

    https://www.amazon.com/gp/product/B019CY4FB4

    I like it because it also has an AC/DC current clamp too... Has been working well for me.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • HorseflyHorsefly Registered Users Posts: 330 ✭✭✭✭
    BB. said:
    This meter also has a "low impedance" mode of ~3,000 Ohms (as I recall):

    https://www.amazon.com/gp/product/B019CY4FB4

    I like it because is also has an AC/DC current clamp too... Has been working well for me.

    -Bill
    Ditto what Bill says. That's the meter I've been using, and I'm very happy with it.
    Off-grid cabin: 6 x Canadian Solar CSK-280M PV panels, Schneider XW-MPPT60-150 Charge Controller, Schneider CSW4024 Inverter/Charger, Schneider SCP, 4 x Vmax XTR12-155 12V, 155AH batteries in a 2x2 24V 310AH bank.
  • TecnodaveTecnodave Registered Users Posts: 356 ✭✭✭
    BB & Horsefly,

    ok ok so I went and checked it out.....looks real good....ordered one,  I do need a DC amp clamp meter better than what I'm using  , love Fluke but Klein does make real good tools,  and this one is IEC 1010 cat 4 , one of my basic requirements,   Amprobe  does too, but from what I've heard Fluke bought Amprobe?  
    2 Classic 150, 2 Kid, 5 arrays 7.5 kw total  2ea.  2S6P Sharp NE-170/NE-165, 1ea. 12P Sanyo HIT 200,  2ea. 4/6P Sanyo HIT 200, MagnaSine MS4024AE, Cotek SK-1500,Exeltech 1100,  2 Banks L-16 battery, Rolls-Surette S-530 and Interstate Traction, Shunts with whizbangJr and Bogart Tri-Metric, iCharger i208B  dc-dc buck/boost converter with BMS for small form lithium 8S 16650 or 10S LiFePO4,
  • MrM1MrM1 Registered Users Posts: 404 ✭✭✭
    Does it do in rush for current peaks like motor starts? 
    REC TwinPeak 2 285W 3S-3P 2.6kW-STC / 1.9kW-NMOT Array / MN Solar Classic 150 / 2017 Conext SW 4024 Inverter latest firmware / OB PSX-240 Autotransfomer for load balancing / Trojan L16H-AC 435Ah bank 4S connected to Inverter with 7' of 4/0 cable / 24 volt system / Grid-Assist or Backup Solar Generator System Powering 3200Whs Daily / System went Online Oct 2017 / System, Pics and Discussion
  • solarhills99solarhills99 Registered Users Posts: 15 ✭✭
    So back to my situation.  I have my array on a garage located 100' from the house and my battery bank etc.  I have a separate ground rod at the garage not linked to the house ground.  When I detach the house from the combiner box and measure array positive to the ground rod I get a reading of the array voltage.  The current is negligible.  Are you saying that this is a function of my cheapo meter and I'm ok with this situation.

    Thanks,

    Charles
  • TecnodaveTecnodave Registered Users Posts: 356 ✭✭✭
    edited May 16 #12
    @solarhills,

    you  are seeing some leakage current from somewhere in the system......if you are disconnecting BOTH positive and negative from the remote array AND negative is not grounded at the array, then this is some leakage. The voltage can be quite high and can present a shock hazard. To mitigate this hazard I would suggest cleaning the array combiner with an electronic cleaner, degreaser to remove built up dust, etc.  I use CRC QD Electronics Cleaner. This product is safe to use on electronic circuit boards, breakers, switches, etc. as it does not leave a residue. Do not in any case use a product such as WD-40 as it leaves a petrochemical residue which will break down during an arc and produce hazardous gas and will destroy contacts as in breakers, switches, etc.  Recheck  voltages.  One or more panels may have a leakage problem from the wiring to the frame, either internally or at the MC connectors.  CRC QD can be used with plastics and insulators as well.   A good multimeter should show this. Check the current with a sensitive meter, if it's only a milliamperes or so it will not not be a hazard but currents of 30 milliamperes can stop the heart!  Normal GFCI outlets trip at 3 milliamperes , the special GFCI for machinery trip at 30 ma. (This is for your concrete floor mounted hydronic zone heater, furnace, etc.). NEC guidance on the issue is to tie the grounds togather,  bonding is the word used in the NEC. If you are in a lightening prone area I would suggest a bare copper 6ga. minimum wire to be connected between the ground rods. This will prevent the lightening from entering the house and will bond the entire system.  On checking the panels themselves disconnect each one individually and check for voltage from wires to frame or cover panel to exclude light and use the ohm's function to check resistance from wiring to frame....it should be 20 megohm or so. 
    2 Classic 150, 2 Kid, 5 arrays 7.5 kw total  2ea.  2S6P Sharp NE-170/NE-165, 1ea. 12P Sanyo HIT 200,  2ea. 4/6P Sanyo HIT 200, MagnaSine MS4024AE, Cotek SK-1500,Exeltech 1100,  2 Banks L-16 battery, Rolls-Surette S-530 and Interstate Traction, Shunts with whizbangJr and Bogart Tri-Metric, iCharger i208B  dc-dc buck/boost converter with BMS for small form lithium 8S 16650 or 10S LiFePO4,
  • BB.BB. Super Moderators, Administrators Posts: 29,002 admin
    That Klein meter does not do peak/surge current measurements.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • TecnodaveTecnodave Registered Users Posts: 356 ✭✭✭
    @ MrM1,

    this is meter does not do peak inrush. There are two kinds of amp clamp meters. This one is a Hall effect sensor as it is AC/DC. Inductive sensors sense inrush current better bur cannot sense DC.   I Have to be very selective in my test instruments as I do live 480 volts including at the primary feed and absolutely require IEC1010 cat 4 instruments as a lightening strike on the power grid miles away from you can induce a 8000 volt spike on the power line. This will explode a cheap multimeter in your hands, with possibly fatal results. Cheap meters are fine on a branch circuit as the capacitance of the wiring will dampen the spike, not to be used in the main box or feeder lines.  
    2 Classic 150, 2 Kid, 5 arrays 7.5 kw total  2ea.  2S6P Sharp NE-170/NE-165, 1ea. 12P Sanyo HIT 200,  2ea. 4/6P Sanyo HIT 200, MagnaSine MS4024AE, Cotek SK-1500,Exeltech 1100,  2 Banks L-16 battery, Rolls-Surette S-530 and Interstate Traction, Shunts with whizbangJr and Bogart Tri-Metric, iCharger i208B  dc-dc buck/boost converter with BMS for small form lithium 8S 16650 or 10S LiFePO4,
  • HorseflyHorsefly Registered Users Posts: 330 ✭✭✭✭
    BB. said:
    That Klein meter does not do peak/surge current measurements.

    -Bill
    Bill - Hate to disagree, but if that is indeed the one I ordered (and it looks like the same one) it *DOES* do peak current measurement. That meter is how I measured the peak current on our well pump before we put in the solar.
    Off-grid cabin: 6 x Canadian Solar CSK-280M PV panels, Schneider XW-MPPT60-150 Charge Controller, Schneider CSW4024 Inverter/Charger, Schneider SCP, 4 x Vmax XTR12-155 12V, 155AH batteries in a 2x2 24V 310AH bank.
  • BB.BB. Super Moderators, Administrators Posts: 29,002 admin
    The meter has peak hold, but does not do "real" peak inrush, as far as I know...

    -Bill "I could be wrong" B.
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • EstragonEstragon Registered Users Posts: 3,583 ✭✭✭✭✭
    I'm not entirely sure there is a problem with leakage current.  When lit, the pv string creates ~Voc voltage between +ive and -ive ends of the string.  It isn't clear if the -ive end is grounded at the house end, but at 100', there likely wouldn't be much of a connection through the dirt to the array ground anyway.

    Presumably, even if floating, string -ive would generally float at something like ground potential (ie ignoring elevation, local thunderstorm, etc.), so reading the string +ive to grounded frame would show something like Voc potential?

    If there's current flowing, I get there's a leakage problem, but does O.C. voltage potential alone mean there's necessarily a problem?  I haven't tried it, so I'm not sure.
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • BB.BB. Super Moderators, Administrators Posts: 29,002 admin
    Read through the Klein CL800 manual.

    Technically called mim/max hold.

    Meter updates 3x per second.

    I would only trust min.max of the value (current, voltage,  etc.) only if the value is present for 1 second or more.

    If the sample period hits the peak surge, you may read closer to the true peak surge current. But this is not the meter I'd use for true peak hold measurements.

    It is an RMS reading meter (root mean square), which means that it does a form of averaging, and probably does not measure/display true peak current.

    Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • TecnodaveTecnodave Registered Users Posts: 356 ✭✭✭
    I ordered the CL800 as well, reading the specs I do not see "inrush current" ,  peak hold is not the same value.
    2 Classic 150, 2 Kid, 5 arrays 7.5 kw total  2ea.  2S6P Sharp NE-170/NE-165, 1ea. 12P Sanyo HIT 200,  2ea. 4/6P Sanyo HIT 200, MagnaSine MS4024AE, Cotek SK-1500,Exeltech 1100,  2 Banks L-16 battery, Rolls-Surette S-530 and Interstate Traction, Shunts with whizbangJr and Bogart Tri-Metric, iCharger i208B  dc-dc buck/boost converter with BMS for small form lithium 8S 16650 or 10S LiFePO4,
  • solarhills99solarhills99 Registered Users Posts: 15 ✭✭
    Thanks for the feedback.  I've checked a separate array/combiner box no such voltage to ground so I'll be checking individual sub arrays on the offending array for leaks.
    Charles
  • TecnodaveTecnodave Registered Users Posts: 356 ✭✭✭
    Charles,

    please   take three. readings of this leakage current, a voltage reading then an current DC reading and a current AC reading, this will probably be a value in the milliamperes range. If it's DC current , it's coming from the array, if it's AC it might be induced current from some nearby wires or powered devices. I'm thinking you have a leakage path within the p.v. Wiring.....the most likely source. I have had MC-3 connectors leak water in and create a ground path , I use vasoline on connectors to keep water out. 
    2 Classic 150, 2 Kid, 5 arrays 7.5 kw total  2ea.  2S6P Sharp NE-170/NE-165, 1ea. 12P Sanyo HIT 200,  2ea. 4/6P Sanyo HIT 200, MagnaSine MS4024AE, Cotek SK-1500,Exeltech 1100,  2 Banks L-16 battery, Rolls-Surette S-530 and Interstate Traction, Shunts with whizbangJr and Bogart Tri-Metric, iCharger i208B  dc-dc buck/boost converter with BMS for small form lithium 8S 16650 or 10S LiFePO4,
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