Wiring a combiner box for quicker installation on site.

LumisolLumisol Registered Users Posts: 374 ✭✭✭
Quick question:
In a combiner box is it acceptable to use wire guages based on the run of that particular wire only or should you stay consistant with the wires being connected to it as well?

Example: I will be using 8awg mc 4 wires to run about 15 feet with 89 volts @17 amps (max amps is 17 but the breakers are 2 10 amps for 20 amps on the line before shutoff) I would like to build the combiner box prior to the installation since it is in a remote off grid location and want to wire the negative lug to an mc4 on the side.
Now according to the charts, I could use as small as 14 awg to connect the connector to the lug (about 6 inches of wire) and I was wanting to ise 12 awg single strand romex for this short internal connection since I have a roll of it sitting around. The lugs will accept anything from 14 to 6 awg. 
Would it be fine to use the smaller gauge inside for the short run from the connector to the lug and then the 8 awg for the long run?

Comments

  • westbranchwestbranch Solar Expert Posts: 5,128 ✭✭✭✭
    Short answer, use the largest wire that you can fit in the CB that matches the final number of PV runs you will use for the Combiner to CC.  Larger is never a problem but if you undersize ( @ minimum) you may have to replace it in the future...but do not oversize your B's... stick to the makers recommendation of amp rating.
    The lugs will accept anything from 14 to 6 awg.
    The manufacturers use 10Ga stranded  AFAIK  for almost all PV to combiner for a reason (safety) and you want to go smaller to 14 and 12?
    I have nothing in my combiners smaller than 10ga solid, after that I use 8 ga stranded..

    hth


     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
  • LumisolLumisol Registered Users Posts: 374 ✭✭✭
    No, I was going to use what I had, if I am going to buy new, I'll buy the 6 awg that will just fit.
    Do your combiners have a larger or smaller than 89 volts at 17 amps total combined in them?
  • westbranchwestbranch Solar Expert Posts: 5,128 ✭✭✭✭
    edited May 2017 #4
    that is almost the same output in the 2 array combiner - combination I have right now. 2 x [ 4 x 140W  panels, 17.9V,  7.85A ]  but we are at 3000 ft and see more V in the cool air...
    ADD: in BOLD
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
  • LumisolLumisol Registered Users Posts: 374 ✭✭✭
    I am at 6500 feet at the mountain place. I have 4 290 watt panels. It can get to 80 degrees there in the summer.
  • westbranchwestbranch Solar Expert Posts: 5,128 ✭✭✭✭
    Which CC are you going to use?
    What is the coldest winter temp you get?
    What did the string calculator tell you for the max # in series for those panels?
    I calculate about 3.26A Imp per panel if 89 V is correct = 13.04A  for all 4 combined.
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
  • LumisolLumisol Registered Users Posts: 374 ✭✭✭
    Which CC are you going to use?
    What is the coldest winter temp you get?
    What did the string calculator tell you for the max # in series for those panels?
    I calculate about 3.26A Imp per panel if 89 V is correct = 13.04A  for all 4 combined.
    http://string-calculator.morningstarcorp.com/#manufacturer=424&module=10510&product=0&vmin=55.2&vmax=56.2&tmin=5&tmax=86&tminunits=f&tmaxunits=f&preview=1&stringnum=2&modulenum=2
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