4x100w panels in parallel - to fuse or not to fuse

[Zil]

If both the positive and negative become shorted:

• Something has gone seriously wrong
• You can't get a shock (it's shorted)

Put an over rated Double-Pole switch on the feed and worry about the important things.

Could have a fire.

 

[PVorBust]

With three or more panels in parallel each panel needs be fused at the labeled max fuse rating. For my Renogy 100W panels that is 15 amperes.

Under what circumstances would a 15A fuse blow while "protecting" a 100W panel?
[making an assumption your 100W panel is 21Voc, that's about 5A]
So I repeat the question: When will a 5A panel blow a 15A fuse?

Fuses are one of the simplest electronic components, but still poorly understood.
A 15A fuse is rated to "operate" up to 15A, not blow at 15A. So even if one of your panels goes short-circuit and the other two feed their full current (10A) into the short, your 15A fuse still won't blow.

Have a look at this data sheet from Littlefuse: https://www.littelfuse.com/media?re...d73-a6c8-aca6d27b9a37&filename=spfi-datasheet
Is clearly shows a 15A fuse will carry 19A for 1000 seconds (16 min) before blowing (see the graph below).
Even with 30A going through it, a 15A will take 1 minute before it blows.

Could have a fire.

Possibly, but a fuse won't save you.

 

[12VoltInstalls]

15A fuse is rated to "operate" up to 15A, not blow at 15A. So even if one of your panels goes short-circuit and the other two feed their full current (10A) into the short, your 15A fuse still won't blow

That is why I fuse stuff for the load even if the wire is 20A. (Not to say anyone should under wire something and rely on a fuse, either, fwiw)
It’s always been a mystery to me- and how common it is- that in small systems people use a 1500-2500W inverter and then feed a breaker box with a a 30, 40, or 50A main breaker. Might as well skip the ocp altogether!