I bought a house in Massachusetts (USA) that was built around 2009. It has a generator with a service rated automatic transfer switch (ATS) connected to a main panel that is set up as a main panel (NOT a sub panel). I don't know if the generator was there from the start, or added later.
Everything I have read seems to indicate that my main panel should be set up as a sub panel with neutrals and grounds separated, green neutral bond screw removed, and the GEC + all bonding should take place in the ATS panel. None of this is currently the case.
I'm wondering if this is or ever was code compliant? I have an inquiry out to my town's electrical inspector. I was hoping to also get feedback from the great minds of the internet!
Note that my grounding electrode is my copper water pipe and there are no ground rods by the service entrance. My meter is up at the street ~200 feet away from the house. The meter has ground rods, bonds ground and neutral, and has a 200 amp breaker in it. Three wires run to my house (2 hot 1 neutral) in underground PVC conduit. My inspector confirmed that everything in this paragraph was inspected and met code when inspected in 2009.
Here is a diagram that I made of the current configuration of the ATS + main panel:
Update 1/20/22: Here is a photo of the ATS labeling on the door as requested by @ThreePhaseEel:
Update 1/23/22: The model number for the Briggs & Stratton ATS is 071025 (rev 00)