Would it have been cheaper to use a panel mounted inverter and string those together, like an Enphase?
We don't have grid power, so those little inverters do us no good. And I don't want to use AC coupling on the inverter.
Chris;Since my 1.1Kw array will be mounted on a 6" pipe about 10 ft high I will be using the MC4 connectors and branch connectors then to the combiner/s
You can put two strings together without breakers between the strings. But once you go to three or more strings of panels then you need a breaker in the combiner rated at the fast blow fuse rating for every string to prevent a fire in the event a string shorts out. So those branch connectors are pretty much worthless for anything but a two string array where you can use one to combine the output of the two strings into one pair of wires.
The reason NEC requires a breaker on each string when you have three more more is because if one string shorts out it can handle the short circuit current from one string it's in parallel with it. But it can't handle the output of two (or more) strings.
The peak input current to the controllers from our 6 kW array is 70 amps. But the array is split with 3.75 kW facing south on one combiner (peak 45 amps) and the other 2.25 kW array is east/west facing at 22.5° tilt (peak 25 amps). So I ran #6 THHN from the combiners to the controller disconnects, and from the disconnects into the controllers. The Service Disconnects have 60 amp breakers. I have #4 THHN from the controllers to the DC bus with 100 amp breakers at the bus on each controller.
NEC requires the Service Disconnect breaker and circuit to be rated at 125% of the Service Rating. But that depends on the temperature and what breakers and boxes you use. #6 THHN is rated 75 amps @ 90C. But the terminals in the box and breakers are only 75C rated. So that drops the rating of the circuit and circuit protection to 65 amps. The minimum to pass inspection for a 50 amp high voltage DC Service Entrance into a residence is 62 amps. But the inspector passed it with 60 amp breakers in the Service Disconnects for the arrays.
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Chris
