+ve and -ve fuse holders adjacent for same string

lazzalazza Solar Expert Posts: 334 ✭✭✭

I'm looking at putting in fuses for both the negative and positive cables of the DC side of a PV system. There are 4 strings- system voltage around 600Vdc for a 20kW inverter.

I'd like to know if you can put the +ve fuse holder directly adjacent to the -ve in the combiner box for the same string, as opposed to putting all the positives on one side and all the negatives on the other. Will this risk arcing? Or will there be sufficient separation between the two fuse holders?


  • BB.BB. Super Moderators, Administrators Posts: 30,738 admin
    Should not be a problem... Do you have a link to the fuses/fuse holders you want to use? Finding the specifications/catalog pages (sometimes difficult to find on the web), should clarify those questions.

    High voltage DC breakers are not common (at least in the US) that are rated for >600 VDC.

    Do you have any in Spain that you can get "stacked or ganged" together? Our "standard" breakers can have a rod or clip that fits over 2 or 3 breaker side by side, and if one circuit trips, the other 1/2 breakers are turned off too.

    For systems with two "hot leads" (our 120/240 vac circuits, the 240 VAC versions have two hots, and 3 phase has 3 hot leads) require all hot leads to be turned off (for safety) if one is tripped.

    For floating power systems (where the neutral/negative bus is not ground bonded), we are supposed to have two breakers in the two hot leads. Standard fuses only trip in one leg, and don't satisfy the newer safety regulations.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mike95490mike95490 Solar Expert Posts: 8,875 ✭✭✭✭✭
    There are hi volt DC breakers on the midnight page.   I would use a breaker over a fuse any day.  A fuse is going to cost $$ to replace, you cannot remove them with the system powered ( Touch Safe is not the same as Hot Removable ) 

    This looks to be 4 DC breakers, ganged and wired in series to achieve 600VDC rating

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  • lazzalazza Solar Expert Posts: 334 ✭✭✭
    edited July 2018 #4

    These are the fuse boxes used. As you can see, for ease of connection and string identification I am connecting with +ve´s and -ve´s adjacent.

    This is because it's not actually a combiner box, just a fuse box.

    However, my concern is over arcing.... there's nothing in the standards against it and my guess is it will be ok, but I want to be sure before putting into operation .... please let me know


    ps yeah, breakers would be great, but at this voltage it's very difficult to source anything over 150Vdc... hence the use of fuses
  • mcgivormcgivor Solar Expert Posts: 3,438 ✭✭✭✭✭
    edited July 2018 #5
    As long as the voltage rating of the fuse holder/ fuse is greater or equal to the maximum voltage used, then the side by side mounting on din rail  should be no problem. Be aware however the fuse carrier should never be opened under load, they are not designed as a means of disconnect, for that a DC isolator like this http://m.feeo-solar.com/dc-isolator/dc-isolator-without-mc4.html could be used in conjunction with the fuses you have.
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  • lazzalazza Solar Expert Posts: 334 ✭✭✭
    Cheers for the replies. Yes. SMA has DC disconnect integrated and yes fuse holder rating is 1000Vdc

    So consensus is I can leave system connected this way?
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