Is a fuse a fuse?

[Vintage465]

I'm fusing my solar panels individually in the combiner box before they are combined. Initially, I purchased the 15a MC-4 fuse holder and the connectors. This came out to about 6-1/2" long. Too long for my combiner box with all the other hardware in there. So, can I use any automotive inline type fuse and fuse holder so long as the the fuse size is right and the wire size(10ga) is the same? The reason I ask is the conductor/fuse is real small on an automotive 15a and I always concern my self with not carrying as much juice cause of the small fuse link compared to the 10ga wire? Meaning, is there a "special" solar fuse that carries more juice?

Thanks,

[ktmrfs]

theoldwizard1 wrote:
IIRC, automotive fuses rating are based on a maximum of 32VDC-36VDC. Voltages above that may cause the fuse to blow (48VDC) the fuse to blow "early".

ktrmrfs is spot on with his statements. What people need to understand that the "variability" of a fuse. A 15A fuse will "carry" 16A of current for hours and not blow. It might even carry 20A for several seconds.

Back to the OP original concern. ATO/ATC sized inline fuses older with either 10AWG or 12AWG are readily available online. Although you can get these fuses up to 40A, If I needed a fuse larger than 30A I think i would use a Maxi-fuse. These typically come with 8AWG wire.

voltage above the fuse rated voltage will NOT cause it to blow provided current is at or below the fuse rated current . But voltages above the rated voltage may cause the fuse to continue to arc when it does blow. Just like massive current can cause the arc to continue even below the rated voltage. That's why fuses have max voltage rating and max current interupt ratings.

[theoldwizard1]

IIRC, automotive fuses rating are based on a maximum of 32VDC-36VDC. Voltages above that may cause the fuse to blow (48VDC) the fuse to blow "early".

ktrmrfs is spot on with his statements. What people need to understand that the "variability" of a fuse. A 15A fuse will "carry" 16A of current for hours and not blow. It might even carry 20A for several seconds.

Back to the OP original concern. ATO/ATC sized inline fuses older with either 10AWG or 12AWG are readily available online. Although you can get these fuses up to 40A, If I needed a fuse larger than 30A I think i would use a Maxi-fuse. These typically come with 8AWG wire.

[alaska_dennis]

In parallel panel installation you need isolation more than fusing. Install isolation diodes in place of the fuses.

[Ed_Gee]

Not sure I understand why one would fuse a solar panel. What rating fuse would you use? ...the solar panel is simply incapable of sourcing higher current than its maximum output.....a fuse could never blow. The other end is not a current source assuming it is a charge controller, so nothing that could provide current to blow a fuse there, either..... am I missing something?

[Vintage465]

time2roll wrote:
You have more than two panels in parallel? What are the panel ratings? link?

If you are using MC4 why even have a combiner box? MC4 combiner is fine and you can get #8 MC4 down to the controller if you need it.

Otherwise yes any 12v fuse is fine.

I have a couple reasons for a combiner box. First, it came with a Zamp combiner box that was rather butchered up when the dealer installed the existing Solar. There was MC-4 cable wrapped round and round in circles on the roof and in the attic. When I yank the the butchered Zamp box, something needs to go back in it's place and since I'm adding a third panel, that something might as well be a combiner box to tidy up the roof wiring. And I'm not really using any MC-4 Connections. Was going to use an MC-4 Fuse holder but they don't fit in the combiner box and I'm trying to keep all connections in the box.

[wa8yxm]

Fuse needs to be rated to handle the full voltage of the panel in full sunlight. And for safety I like to double that. So a 24 volt panel would need 48 volt rated fuses (Or at least 36) and DC rated.

The only other thing would be the "inline resistance) of the fuse (The resistance pin to pin not blown) likely too low for your meter to measure but I'm not sure how the "Solar rated" fuses compare to standard automotive/house fuses in this aspect.

And as someone else mentioned... The fuse's "Speed" Fast. slow. standard. ultra fast) That is how quickly it blows if overloaded.

[time2roll]

You have more than two panels in parallel? What are the panel ratings? link?

If you are using MC4 why even have a combiner box? MC4 combiner is fine and you can get #8 MC4 down to the controller if you need it.

Otherwise yes any 12v fuse is fine.

[ktmrfs]

fuses are rated for interupt current, interupt time, and arc interuption voltage. that is how much current before it trips, how long an overcurrent takes before it blows, and how high the voltage can be and still interupt the current and not sustain an arc thus not interupting the current flow.

AFAIK for solar panels, since most are used in houses and many are interconnected to the house power feed and power line there are spec's for the fuses to be used.

Now, when used with a trailer, likely another story. no line connection, no feed to the power grid.

Now I am by no means an expert on this application, but if it was me using a 15A auto blade type fuse and fuseholder I would feel comfortable.

BTW 14Ga wire is rated for 15A, 10Ga wire is rated for 30A in romex, higher in individual strands. The 10Ga gives lower voltage drop.