inline fuses for pv wire

[Texican]

I am getting close to hooking up my 2 ground arrays to my 2 LV6548 inverters.
using 24 panels at 250w each and 6s2p setup, so 2 strings from each array
so each inverter will use both mppt inputs getting around 230v and 17 amps at each input

do I put 1 inline mc4 type fuse on each positive pv wire right before the inverter ?
would I need a 20 amp fuse or a 30 ? 15 is to low for the paralleled strings

or does each string of 6 panels need a 15 amp fuse before it is paralled ?

thanks

 

[rmaddy]

You don't need any fuses with just 2 strings in parallel.

But if you do want a fuse for each of the 2 inputs you would take the Isc of a panel and multiply by 2 since you have two strings in parallel. Then multiply that by 125% (1.25) to get the fuse size.

 

[Texican]

Thanks

 

[rickst29]

I am getting close to hooking up my 2 ground arrays to my 2 LV6548 inverters.
using 24 panels at 250w each and 6s2p setup, so 2 strings from each array
so each inverter will use both mppt inputs getting around 230v and 17 amps at each input

do I put 1 inline mc4 type fuse on each positive pv wire right before the inverter ?
would I need a 20 amp fuse or a 30 ? 15 is to low for the paralleled strings

or does each string of 6 panels need a 15 amp fuse before it is paralled ?

thanks

I must advise that you put class-T fuses on each string, either before or after being paralleled. The reason for these fuses is to prevent a lightning strike, at the ground arrays, from burning down your house.

You pay extra for the class-T fuses, because they will "open" the connection upon a sudden high-voltage, high current spike connection quickly. Lesser fuses are too slow to respond, and will often simply melt into a worthless mess - still allowing current to flow through. The fuse rating for maximum allowed needs to be significantly higher than your 17 MPPT current value I(mp). Anything from 50 to 120 Amps would be a good choice, because anything amount of current above that would imply a natural disaster.

 

[JRH]

I must advise that you put class-T fuses on each string, either before or after being paralleled. The reason for these fuses is to prevent a lightning strike, at the ground arrays, from burning down your house.

You pay extra for the class-T fuses, because they will "open" the connection upon a sudden high-voltage, high current spike connection quickly. Lesser fuses are too slow to respond, and will often simply melt into a worthless mess - still allowing current to flow through. The fuse rating for maximum allowed needs to be significantly higher than your 17 MPPT current value I(mp). Anything from 50 to 120 Amps would be a good choice, because anything amount of current above that would imply a natural disaster.

If one was use class T fuses in the lines leading from the array to SCC , would it be better to do both pos and neg.? Or just pos..? Each cable is already fused in the combiner box 50 ft from the house ,but those are not Gona stop a big surge as you say.
the array at 88 volts only puts out about 30 amps, so if I used the 100/ 125 amp T fuse it would only be activated by something beyond anything the array could do naturally…I had considered this before but find few people that do this …I like the idea…
Are we on the same page about this..?
thank you n advance , Jim

 

[??????]

Resurrecting this thread but I was always under the impression that a MOV (https://www.midnitesolar.com/pages/spd/index.php) was used for lightning strikes A lightning strike will cause a very high voltage spike, but not a high current spike - as such, a traditional fuse wouldn't protect against a strike.

As far as fuses to be used, MC4 inline fuses appear to be an option: https://www.altestore.com/store/enc.../staubli-mc4-in-line-fuse-15a-1000v-dc-p9885/ from what I can gander, this is only needed when putting more than 2 strings in parallel, since the ISC (short circuit current) of the panel is (usually) less than the carrying current of the conductor (PV or home run wire).

There are some other possibly-sketchy solutions (https://www.amazon.com/Solar-Odyssey-Holder-Waterproof-Connector/dp/B09WZLHXC4) that appear to use an RT14 style ceramic fuse. From what I can tell, this style fuse is rated for AC, not DC, current, and I'm not confident it'd break a DC arc under load. I think that's why the staubli inline MC4 fuse (altestore link above) is so long - all that length likely has silica or some other material designed to arrest the arc to stop current.