Three ONCCY fire-safety shutdown isolators with MC4 connections: ERS40-6-MC4 for three strings, ERS50-8-MC4 for four strings and ERS40-10-MC4 for five strings.
Count channels, not strings. The number in the code is the channel count and each string takes two of them, which is why the -6 covers three strings and the -10 covers five. Choosing on the string figure alone is how a unit ends up a channel short on site.
The MC4 ends mean the device goes in on the roof, in line with the array, so the DC is broken up there rather than only at the inverter.
