Dual breaker switch between solar panels and MPPT

[earthbm]

1. Why do you need to have it?
(Dual = both positive and negative)

What’s the contingency it is meant to cover?

2. If you have it, what brand/kind?

[Celestialsailor]

My understanding is you only need a switch rated for the current on the "+" side of the wiring...meaning the red wire.

[RaymondR]

I have a couple of solar regulators which common the positive and do all the switching and regulation on the negative. I also have ones which common the negative and do the switching and regulation on the positive. Perhaps it's to take care of both contingencies when isolation is required.