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diy solar

Micro inverters with multiple strings - how to set up the safety cutoff?

Proteus

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Oct 19, 2020
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I'm relatively new to the whole world of solar and have educated as much as I can but I'm getting conflicting information so I figured I'd turn here for some help. Here's my steup:

20 400 watt panels
5 QS1 micro inverters
Unirac racking

Since the max panels in a QS1 string is 12, I have two strings. This means 2 AC lines of 20A each.

My original plan was to terminate both strings in a junction box and then make two runs from the junction, through conduit, to my service panel where I'd put two 240V 20A breakers for inputs. I have to have a safety cutoff to be code compliant and for the life of me I can't find a solution. One "expert" has told me I need a combiner for AC that has its own breakers and that will have a single output to run through the cutoff, then to the service panel. I'd obviously have to have a larger breaker at the panel since there would be two 20A feeds combining. This seems expensive and completely unnecessary. The second expert has told me there's no real cheap way to do it but the most effective would be to just put two small knife safety cutoffs - one for each string - and run each to the service panel with a 20A breaker for each. What I'd prefer to do is find a cost effective cutoff with more connections inside to accommodate two AC runs but there doesn't seem to be an inexpensive solution. What am I missing here?
 
you got like $5k + of equipment listed. and your hand wringing over a couple hundred dollars worth of shuttoff panels?

It also seems like the QS1 are single phase 240v output which suggests your location is not in NA. If thats the case I defer to the people that know the standards for your area.
 
It's not the cost it is the elegance of install. I'd prefer a single cutoff but if not an option, I'll just do two.
 
My DC system was designed without disconnects between the solar panels and my inverter.
The inverter has a disconnect and rapid shutdown is required in my area.
So, I don't think I need disconnects but the passthrough box for going from PV wire to conduit in my system design costs $200.
I have been thinking about replacing the pass through box with isolators from this company - https://www.factorymation.com/
They sell AC disconnects too and they have live chat. Maybe they can help you out.
Someone else will probably come along with more ideas
 
Every state or for that matter city have there laws. My system is very close to yours. Where I am you would have to come down to a combined box and then to a single cutoff. Then to your panel . I don't know about where you are. He has micro inverters.
 
One 40A or larger DPST switch. One side goes to 40A breaker in your panel. Other side goes to four touch-safe fuse holders or two 2-pole breakers on a DIN rail inside the switch enclosure.

Not sure if either of these has the space inside. I did it with a 100A switch with fuse holder. It was tight, would have been easy without fuse holder.


 
My switch was a blade type with a fuss in it. But again different rules in different places. For that mater Three sets of rules I had to meet State, city, and utility.
 
Ok, family issues galore and my solar project has been sitting in crates for a year. I'm finally set up for the last part of the install. I have all the racking installed, braced, and ready to go. My plan is the following: From the AP Micro inverter strings, they output black, red, and green. I will go from each string to an outdoor junction box per the manual and wire tie those in the junction box. From there, I will take each string to a fusible cutoff 240 single phase and purchase a grounding bar for it so I can go ground in and then ground out. 3 wires (black, red, ground) will enter each cutoff and exit into conduit. I will run both conduits 18" below ground and into the barn. Inside the barn will be a metal junction box and from there I will make two runs of MC 12/2 the 45' or so to the sub panel and put two DPST 20A 220 circuit breakers. Black to one pole, red to the other, and the ground to the ground bar in the panel.

According to the AP micro manual, the system is grounded through the micro inverter wiring and no additional grounds are needed.

Am I missing anything obvious here? I've done a lot of basic electrical work -- both 220 and 110 but this is all new to me and I don't want to make a mistake...
 
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