10awg + 10awg wire in parallel=?

My PV array's are some distance from my (3) XW-MMPT-60-150 SCC's.
I am using 10awg rubber insulated 2 conductor + ground cable from the combiner boxes to the SCC's
The cable is rated for 90* C.
The distance is around 60' from PV tp SCC. (30' MC4 cable + 30' of the 2 conductor)
Since I have a large roll of this wire, I was thinking of stringing in parallel another run of the same wire from PV arrays to the SCC.
Is this a viable idea? What would the gauge be of the combined 10awg?
(4) 195 watt 17.5 VMP panels in series per array.
(2) arrays per string
(3) strings
Thanks

Comments

  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: 10awg + 10awg wire in parallel=?

    if you do that it would be #7. nec frowns on doing that though. you can use the v drop calculator in my sig line to figure the drops for yourself.
  • deacondeacon Solar Expert Posts: 33
    Re: 10awg + 10awg wire in parallel=?

    Thanks for the quick reply--viewing your link now.
    Rich
  • BB.BB. Super Moderators, Administrators Posts: 30,625 admin
    Re: 10awg + 10awg wire in parallel=?

    The issue with parallel wire runs is that if one wire fails, the second is now carrying 2x the current and you have no way of knowing it failed.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • waynefromnscanadawaynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: 10awg + 10awg wire in parallel=?

    I did that with the almost 400 foot one way run from my micro-micro hydro. One cable pair was enough to handle it ok, but doubling up on it cut my loss in half. In my case, if one run opens up, there is no danger, just that my loss will increase a bit. Was trying to wring every last watt out of the system. One run was already installed and buried, I had cable for a second run, so figured why not :roll:
  • solarixsolarix Solar Expert Posts: 713 ✭✭
    Re: 10awg + 10awg wire in parallel=?

    3 awg sizes are the same a doubling the wire size.
    For example, two #10 = one #7 or 4 #10 = one #4
    not a good practice though.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: 10awg + 10awg wire in parallel=?

    If you feel you must do it, use separate fuses per wire; each sized for 1/2 current.

    Wayne's install is okay because one wire is sized to handle the full expected current; the second reduces V-drop. You get into trouble when you substitute two of a smaller size for one of a larger.
  • JburgessJburgess Solar Expert Posts: 130 ✭✭✭
    Re: 10awg + 10awg wire in parallel=?

    You may have trouble getting past inspection,

    From NEC 2008:

    310.4 Conductors in Parallel.
    (A) General. Aluminum, copper-clad aluminum, or copper
    conductors of size 1/0 AWG and larger, comprising each
    phase, polarity, neutral, or grounded circuit conductor shall
    be permitted to be connected in parallel (electrically joined
    at both ends).
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: 10awg + 10awg wire in parallel=?
    Jburgess wrote: »
    You may have trouble getting past inspection,

    From NEC 2008:

    310.4 Conductors in Parallel.
    (A) General. Aluminum, copper-clad aluminum, or copper
    conductors of size 1/0 AWG and larger, comprising each
    phase, polarity, neutral, or grounded circuit conductor shall
    be permitted to be connected in parallel (electrically joined
    at both ends).

    Um, shouldn't that say "shall not be permitted to be connected in parallel"?
  • john pjohn p Solar Expert Posts: 814 ✭✭✭
    Re: 10awg + 10awg wire in parallel=?

    Cariboocoot I always thought the same that #1 and #0 etc could be connected in parallel. ?
  • JburgessJburgess Solar Expert Posts: 130 ✭✭✭
    Re: 10awg + 10awg wire in parallel=?

    It basicaly says that only #0 and larger can be used in parallel. #1 and smaller are not allowed in parellel.

    What I posted earlier is cut and paste from the PDF.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: 10awg + 10awg wire in parallel=?
    john p wrote: »
    Cariboocoot I always thought the same that #1 and #0 etc could be connected in parallel. ?

    Not sure. Out here in the middle of nowhere we tend to go by "good practice" more than "NEC". So far no electrical fires from any of my work. :roll:
  • JburgessJburgess Solar Expert Posts: 130 ✭✭✭
    Re: 10awg + 10awg wire in parallel=?

    It is important to remember laws and rules don't have to logical, reasonable or fair. It's just what the whim of politicians was at the time.

    I just mentioned it in case an inspection was required.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: 10awg + 10awg wire in parallel=?
    Jburgess wrote: »
    It is important to remember laws and rules don't have to logical, reasonable or fair. It's just what the whim of politicians was at the time.

    I just mentioned it in case an inspection was required.

    'Struth! :p

    Take the NEC section on DC GFCI .... :confused: Let's not even go there.
  • john pjohn p Solar Expert Posts: 814 ✭✭✭
    Re: 10awg + 10awg wire in parallel=?

    CARIBOOCOOT I just looked up some rules here in aus and it appears that #0 and above is acceptable to parallel. In Philippines its ok to.parallel anything that has slightly better electrical properties than wet string.;)
    Im a sinner and have paralleled cables smaller than #0. even #4. as they a damn site easier to get around tight corners..:-)
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: 10awg + 10awg wire in parallel=?

    I still don't like their wording: "shall be permitted".
    Shall implies should or must. Couldn't they just say "may be"?
    Legalese; divorced from English. :roll:
  • ggunnggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: 10awg + 10awg wire in parallel=?
    Um, shouldn't that say "shall not be permitted to be connected in parallel"?
    No, it says that it's OK for 1/0 and larger. Implicit in that statement is that anything smaller is not OK. The OP's question was about #10.
  • deacondeacon Solar Expert Posts: 33
    Re: 10awg + 10awg wire in parallel=?

    Gave it a lot of thought and ran up to Hunt Electric and bought a 300' spool of single strand #6 AWG.
    I Made six cables for the controllers ( positive and neg)( routed them different and saved 15' of run).
    Voltage looks much better, and producing more power.
    This site is a great wealth of advise and information.
    I don't have to worry about inspections, I am out in the country and not using the grid for my system at all.
    My PV arrays are in my pasture, and all the hardware is in my barn.
    I do my best to wire up everything safe, and if possible go with a higher rating if possible.
    Thanks again,
    Rich
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