Questions regarding planning a new system.


New Member
Oct 22, 2021
I am new to solar, and am trying to learn as much as possible. I like the Enphase IQ8 series of micro-inverters, though the only reason I see someone using them is for solar-backup only. I am located in So Cal, so I am must likely regulated to a grid-tie with battery backup. I only have a 100A main breaker in my panel. I don't know if the bus-bar is 125 or 100, I will assume it is 100. My understanding is I am allowed a 20A breaker for a PV array, which would = 3840 watts.

My questions are:

In thread "Off grid for my house" post #22 @Hedges has the following

My Square D QO panels have 225A busbar and 200A main breaker.
225 x 1.25 = 270A
270A - 200A = 70A backfed PV breaker allowed
70A x 80% = 56A continuous current
56A x 240V = 13,440W

Where does the 1.25 come from. Is it based on fuse size?

Would the max array size I am allowed be = to 4800 watts vs the 3840 watts.
100 x 1.25 = 125A
125A -100A = 25A
25A x 80% = 20A
20A x 240 = 4800W

I currently use about 6600kwh/year. I would like to future proof a system that allows expand-ability, is this possible.

Is it possible to have 2 strings of panels each going into the IQ combiner and 1 input for battery backup.
1 string would be mounted W or E 90° of each other. Just like @Hedges mentioned in post#16 of the mentioned thread above.

If I go with the Enphase IQ7+ or IQ7a, can I use a battery besides the Enphase battery. Is it possible to use the Signature Solar EG4 batteries.

I am trying to figure this out before I lose the opportunity for NEM 2.0

Sorry if my post is all over the place

Bri from IA

New Member
Nov 27, 2020
Perhaps you should reach out to the person who wrote the post. I'm not able to follow the logic of his calculations.

That said, 1.25 and 80% (i.e. 0.8) are recipricals of each other. That amount is commonly used in sizing fuses and circuit breakers. For example, if an appliance requires 10amp for operating current, the breaker/fuse should be sized 12.5A minimum so I won't trip/blow while the divice is running.

You might consider going over options with a licensed electrician, even if you have to pay them for advice. You'll be able to move more quickly and cover more topics in a quick manner.