Wire size question

Received my (44) JASolar 370w panels for a grid tied system. It will have 4 strings of 11 panels with DC Voltage 408v and 10.2 amps per string. The PV wire on the panels are 12 AWG and have at least 50 fine strands (I did not count them all).

My electrical permit drawing also shows 12 AWG PV wire.  When I look at buying 12 AWG PV wire, it has only 7 strands.  If I buy 10 AWG PV wire it is available in 7 or 19 strands.  My longest run for the PV wire is 30' in conduit.  

Will I see much of a difference between 10 AWG and 12 AWG or is ok to buy the 12 AWG PV wire with 7 strands?

Comments

  • BB.BB. Super Moderators, Administrators Posts: 30,502 admin
    The finer the wire strands, the better able the cable will be able to flex without work hardening the copper. Also, smaller stranded cable can be easier to pull through conduits.

    Solid and low strand count wiring, works well with typical binding screws found in solar bus bars, charge controllers, etc. Very fine wire tends to move and "squirm" out of the pressure point and make for poor long term connections (does depend on the design of the wire connections).

    Also when using crimp connectors, very fine strand wiring has a larger overall diameter because of the "air space" between strands. For very fine stranded cable, may need a different crimp connector made for that application.

    For our typical usage, 1/7/19/50+ stranded cable--Does not affect current capacity of the cabling. There is something called the skin effect, but for our normal system designs, does not really affect anything:

    https://en.wikipedia.org/wiki/Skin_effect

    Using a voltage drop calculator for 30 feet / 10.2 Amps / 10&12 AWG:

    12 AWG:
    Voltage drop: 0.97
    Voltage drop percentage: 0.24%
    Voltage at the end: 407.03

    10 AWG:
    Voltage drop: 0.61
    Voltage drop percentage: 0.15%
    Voltage at the end: 407.39

    No appreciable difference between 0.24% and 0.15% voltage drop (from an engineering point of view). You are well below 1% voltage drop with either wire AWG. With the heavier cable, you would get ~0.1% more harvest.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • DesertRatDesertRat Registered Users Posts: 11 ✭✭
    Bill,
    Been off computer for a while and did not notice your reply.  So I guess I would be safe using the 12 AWG 7 strand PV wire.  One opther question if you know.  Panels have QC4.10 connectors.  Do you foresee and crimping problems using the 7 strand wire?

    -Tom
  • BB.BB. Super Moderators, Administrators Posts: 30,502 admin
    No problem--Hope life has been treating you well.

    Generally, course stranded cable is not a problem with crimp connectors (solid vs course stranding). When you get the fine welding cable type--That is when a standard size house wiring crimp/connection can be a problem (fine stranded wire > AWG rating for "house type" wiring).

    Don't know anything about QC4.10 connectors.

    http://pv-cables.com/Connectors_Splices-QC4.html

    It looks like they are uprated versions of the MC4 connectors. Both voltage (1,000 VAC) and current.

    This one says they mate with MC4 and H4 connectors:

    http://www.qc-solar.com/product/678

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • PhotowhitPhotowhit Solar Expert Posts: 5,173 ✭✭✭✭
    DesertRat said:
     Panels have QC4.10 connectors.  Do you foresee and crimping problems using the 7 strand wire?
    I've never used those connectors, but 7 strand in MC4 connectors is a PITA! Spend the extra on 19 strand, or be prepared to spend some time getting them right. Anvil type crimpers work better than hinged type. There's a thread here where I went though a bit more in depth.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, 660 ah 24v ForkLift battery. Off grid for @16 of last 17 years. Assorted other systems, and to many panels in the closet to not do more...lol
  • BB.BB. Super Moderators, Administrators Posts: 30,502 admin
    I think this is the post that Photowhit is referencing regarding the "good" crimping tool:

    https://forum.solar-electric.com/discussion/comment/405180#Comment_405180

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • DesertRatDesertRat Registered Users Posts: 11 ✭✭
    Bill,
    Thanks for the link and info and kudos to Photowit for the nice article for reading.  So I will look into the 19 strand wire.  On another note trying to find a connecting tool for the QC4 connectors.  The MC4 tool is too small and will not fit on the barrel end.  Just sent an email to QC solar products but in the meantime if I cannot find the proper tool what other ways are there to tighten the barrel after assembly so as not to mark up the barrel.  It seems like a pair of pliers with a rag is not a good idea.  Any suggestions.

    -Tom
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