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In this case the generators themselves worked, just not the mechanism to cut over to them.

Generally called a "static switch", and they are prone to issues. Here's one: https://www.aegps.com/en/products/ups-accessories/static-tra...

Are they automatically a single point of failure or can you install several of those on one site?

I include that bit of the system in "backup generator" to distinguish it from "generator".