Proper In Line Fusing Calculation?

[rcnjstudent]

Specs of my 4x Renogy 12v 100W Panels:
Short-Circuit Current (Isc): 5.21A
Maximum Series Fuse Rating: 15A

Getting conflicting info and can't seem to find a reliable source of info on this. Want to make sure I get this done properly to keep everything safe. Looking to connect these 4 panels in parallel using this 4 to 1 branch adapter www.amazon.com/dp/B08NV5PB9X and want to make sure they are fused properly:

This site says to do sum of Short Circuit Current for all Panels. If sum is greater than Max Fuse Rating, then fuse must be Max Fuse Rating. In my case, using his guidance, this gives me a fuse size of 15A.

How/When to Fuse a Solar Panel Array

This blog post is going to teach you how to determine when and if you need to add in-line fuses when designing a camper solar array. Sometimes you need to fuse your solar array, and

www.explorist.life

HOWEVER...
This says to do Sum of Amps * 1.25% to get proper amp fuse size. Doing the math ((5.21 * 4) 1.25), this gives me 26, which would require a fuse size of 30Amps if we round up.

How to Fuse your Solar System

By Stephen CliftonTechnical RepresentativeWhen hooking up your Renogy system, the best way to add protection is by using fuses or circuit breakers. Fuses and circuit breakers are used to protect the wiring from getting too hot and also protect all devices connected in the system from catching...

renogy.com

Which calculation is accurate to make sure that I'm safe? Seems like there's a lot of different opinions on how to calculate this online and I want to be absolutely certain that I am getting the proper capacity. Thanks in advance!

 

[chrisski]

To be sure we're talking the same thing, you need to fuse all four branches. So you'll need 4 fuses at 5 * 1.25, which honestly the sizes are 5, 10, and 15. I'd get a 10 amp there.

https://www.amazon.com/dp/B00YG1DY20/

The second calculation is also correct with 30 amps, but that is for after they are joined before the SCC. What I do there is put a properly rated for on and off 30 amp circuit breaker in so I can shut off power to the solar panels easily for storage and also for troubleshooting.

Like this

Amazon.com: DIN Rail Mount Combiner PV Breaker - 30 Amp, 150 VDC, | MNEPV30 : Patio, Lawn & Garden

Amazon.com: DIN Rail Mount Combiner PV Breaker - 30 Amp, 150 VDC, | MNEPV30 : Patio, Lawn & Garden

www.amazon.com

I don't know an official definition of the Max series fuse rating, but what it means based off the forums are once your panels are in parallel and they can exceed that value, each parallel string in the array needs to be fused. Nearly always is once more than two strings are in parallel each needs fusing. 15.63 for three strings is greater than the 15 amp Max series fuse rating, so you need to fuse each string when three or more are in parallel.

What's bad about those branch connectors and you are under the limit, although the branch connector can be rated to higher than 30 amps, the MC4 plug it goes into is not.

 

[BradCagle]

Max series fuse rating of your panels is 15Amp. This means everything on a single panel is safe up to 15A, the cells, the junction box, the diodes, the traces, the wire the connectors all can handle this current.

You can safely parallel 2 of these panels with no fuse because max short current is 10.42a (2 x 5.21a), but any more than that puts you over the 15a series rating.

So for your 4 panels in parallel you need 4 x 15a inline fuses, 1 for each panel to properly protect everything.

10a fuses should work fine too.