Is fusing panels needed?

Hello All,

I am installing 4 x 130W Kyocera in parallel on my motorhome. The wiring will be #10 from each panel to a combiner box on the roof and then #4 down to the controller. There will be a 40A fuse just before the controller in the #4 wire.

Do I need to install fuses in the combiner box for each panel?

Thanks Jim


  • BB.
    BB. Super Moderators, Administrators Posts: 33,471 admin
    Re: Is fusing panels needed?

    You need to look up the specs for the Kyocera panels and find the series protection fuse/rating.

    But the answer is probably yes... You have 40 amps available (assuming a controller fault), or roughly ~7amps*4=28 amps from the four parallel panels and you need to protect the relatively small solar panels's current paths and their wiring. You want the fuses/breakers to ensure that a short/failure anywhere in the system or the panels themselves will not run the risk of causing a fire (including the need to protect your #10 wiring from shorting--a 40 amps fuse is probably too large--use the NEC+the spec. sheet to find the proper size fuses).

    Probably--you will never have a fault that pops the fuse(s). But if something bad happens on your RV (say a baseball through a solar panel), you would want the proper protection.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Is fusing panels needed?

    i don't know if the nec comes into play on this for a trailer as crewzer could say on that for sure. if it turns out to be not required by law then during the install i would initially have them fused anyway as someone awhile back chimed in saying he connected the pvs up wrongly by wiring one in backwards giving a giant short between the pvs in question and they didn't work after that. if you're going to initially fuse them you might as well leave them fused. breakers are sometimes a good option too, but fuses on individual pvs can be done cheaply.
  • crewzer
    crewzer Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
    Re: Is fusing panels needed?

    I agree with Bill's discussion about protecting the one module's small wire from the output current of three modules, espcially once you factor in temperature derating.

    This handy fused distribution box can be used "backwards" as a fused combiner in 12 V systems: It's about $35 from West Marine.

    Jim / crewzer
  • System2
    System2 Posts: 6,290 admin
    Re: Is fusing panels needed?

    Thanks Guys,

    The panel rating for fuses is 15A. I built a combiner box out of a 6x6x4 plastic weatherproof box. Installed 2 terminal strips, one + the other -, and have room for 4x15A flat blade fuse holders to be mounted on the + terminal strips.

    I am using a Blue Sky SB50 for a controller and the 40A fuse is at the controller in the #4 from the roof.

    I had already bought the #10 wire fuse holders, but on the Escapee RV site most were 50/50 on the issue.

    Since I have them, I will use them.

    Thanks Again,

    '96 Safari MH, 300 CAT