This was a lot of fun to reverse engineer. Mainly because it's very oldschool inside. It's an automatic changeover switch for a backup generator supply. When power fails and the generator starts, the switch will automatically transfer over to the generator. When the power returns it will switch back over to the main supply.

The issue with the relay being energised all the time and to make it generatorpriority could be addressed by simply swapping the sides the main and generator power are attached to. That way the generator would take priority in the event of a power failure and not switch back until it was turned off, and the relay would only be energised when the generator was running.

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