Roof mounted microinverter pv system - combiner box not needed

[SunEagle]

Another unnecessary snide remark .

From what I understand, the panels sparked, and the sparks caused the fires. I'd also guess that since it's a commercial installation, it doesn't use microinverters and is therefore a DC system running at voltages closer to 400 or 600 VDC rather than 240 VAC and that here were fuses installed.

For future reference when I post using the Comic Sans MS font followed by I am trying to be sarcastic and a little funny. Please don't take that post seriously.

[Mike90250]

Protecting it from what? Somehow one or more inverters break and put out a lot more current - or is it just an NEC thing - must protect the wire even if it's impossible to overload it?

Are you saying it's okay to combine the strings without an intermediate 20 amp breaker or fuse?

a light fixture only consumes an amp or so, but the WIRES are protected by the 20A breaker or fuse at the main panel.

If the inverter faults, or a rat chews a wire you could easily get a fault needing a breaker to activate

[Markyrocks69]

On DIY systems, I've noticed that if the DIY'r doesn't use a combiner box, they still run each string to a 20 amp breaker before combining the strings and connecting to a back fed breaker in their service panel. The Enphase design guide promotes this as well.

My question is this: Since the only limiting factor for the number of microinverters in a string is the 12 AWG Q cable ampacity rating (20 a), why can't the strings just be wire nutted together in a J-Box on the roof with a 10 AWG home run taking all the power to the back fed breaker I the service panel.

I don't understand the purpose of a combiner box with a 20 amp breaker for each string. The breaker will never flip, especially with only 8 microinverters (total current = 10.32 a).

I had read up on this in regards to the DC side of solar but in reference to the ac side the concept your missing is that if you have multiple circuits combined and one of the circuits have a ground fault it could potentially pull the electricity in the opposite direction down the circuit towards the panels. Since these circuits combined eventually end up in the main panel, that shorted circuit could pull the maximum amperage of the breaker in the panel AND whatever amps are on whatever the other combined circuits have on them aswell b4 the breaker pops far exceeding the ampacity of the 10 or 12 gauge wire.

I'm sure what youre describing is against code in one way or another. I couldn't possibly see it surviving an inspection.